Topic 1: The Challenges of Infectious Diseases (SK297) PDF

Topic 1 The challenges of infectious diseases **SK297 Infection, immunity and public health** **Topic 1 The challenges of infectious diseases** This publication forms part of the Open University module SK297 *Infection, immunity and public health*. Details of this and other Open University modules can be obtained from Student Recruitment, The Open University, PO Box 197, Milton Keynes MK7 6BJ, United Kingdom (tel. +44 (0)300 303 5303; email general-enquiries\@open.ac.uk). Alternatively, you may visit the Open University website at www.open.ac.uk where you can learn more about the wide range of modules and packs offered at all levels by The Open University. The Open University,\ Walton Hall, Milton Keynes\ MK7 6AA First published 2024. Unless otherwise stated, copyright © 2024 The Open University, all rights reserved. All rights reserved. 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In using electronic materials and their contents you agree that your use will be solely for the purposes of following an Open University course of study or otherwise as licensed by The Open University or its assigns. Except as permitted above you undertake not to copy, store in any medium (including electronic storage or use in a website), distribute, transmit or retransmit, broadcast, modify or show in public such electronic materials in whole or in part without the prior written consent of The Open University or in accordance with the Copyright, Designs and Patents Act 1988. Edited and designed by The Open University. WEB 14087 6 1.1 Contents ======== - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Introduction ------------ In this module, you will learn about a wide variety of infectious diseases and public health approaches to monitor, prevent and control them. Topic 1, Part 1 introduces you to the broad area of public health, especially within the context of infectious disease, and some of the socio-economic factors that make disease outcomes worse. You will learn about the global scale of infectious diseases and how they are exacerbated by poverty, hunger and climate change. You will learn how public health is organised into three 'pillars' to combat disease: health protection, disease prevention and health promotion. In Part 2, you will learn about how infectious diseases can be characterised, the broad range of pathogens that cause disease, and where in the world most deaths occur due to the major infections: tuberculosis, HIV/AIDS, malaria and COVID-19. You will then consider the various origins of infectious diseases and some of the societal factors that allowed many diseases to become epidemics. Start of Media Content []{#Session1_MediaContent1.anchor}Video content is not available in this format. **Video** Topic 1 introduction. [View transcript - Video Topic 1 introduction.](#video-topic-1-introduction.) End of Media Content Learning outcomes ----------------- Module learning outcomes are given in brackets after each topic learning outcome. You can review the module learning outcomes in the [SK297 Module guide](https://learn2.open.ac.uk/mod/oucontent/olinkremote.php?website=SK297&targetdoc=Module%20guide:%20SK297%20Infection,%20immunity%20and%20public%20health&targetptr=4.2). After studying this topic, you should be able to: - - - Planning your study ------------------- This topic should take you about two weeks to study. During these two weeks you will also be introduced to the COVID-19 case study and do some forum work with other students as part of TMA 01. - - - Part 1 Introducing public health -------------------------------- Introduction to Part 1 ---------------------- This part introduces you to the three major pillars of public health, which are central to the module's content, namely: - - - We will also cover some fundamental concepts in public health, such as assessment of population health needs, how health needs vary among different population groups and geographic locations, and how health needs change over the stages of life. We will then contextualise the concepts of public health within the context of infectious disease by discussing the global scale of infectious diseases and how they impact different communities. 1.1 Introduction to public health ---------------------------------- Start of Activity **Activity 1.1 Part 1 What is public health?** You should allow approximately 10 minutes for this activity. Start of Question This activity will help you to achieve [learning outcome 1.1](#learningoutcomes). End of Question Start of Question Before reading any further, enter three or four words that you currently think best describe 'public health' into this word cloud. At the end of this part of the topic you will revisit this word cloud and see if your thoughts have changed. Start of Media Content Interactive content is not available in this format. End of Media Content End of Question End of Activity Public health has been succinctly defined as 'the science and art of preventing disease, prolonging life and promoting health through the organized efforts of society' (Donald Acheson, UK Chief Medical Officer, 1988, paraphrasing a longer, original definition, by the American public health expert Charles-Edward Winslow in 1920). Start of ITQ - - End of ITQ On the whole, society is responsible for public health. This ranges from global organisations, such as the World Health Organization (WHO), responsible for setting large-scale goals, down to individual members of society who make personal decisions on maintaining their own health. Start of ITQ - - End of ITQ 1.2 Basic concepts of public health ------------------------------------ Public health is a broad term that deals with all aspects of maintaining or improving people's health and wellbeing. It includes **communicable** (infectious) diseases, which are the focus of this module, but also **non-communicable** (non-infectious) diseases and health conditions, such as cardiovascular diseases, cancers, chronic respiratory diseases, diabetes and mental health conditions. Public health activities can work at the level of a group (e.g. age, ethnicity and biological sex assigned at birth (see the [SK297 Module guide](https://learn2.open.ac.uk/mod/oucontent/olinkremote.php?website=SK297&targetdoc=Module%20guide:%20SK297%20Infection,%20immunity%20and%20public%20health&targetptr=4.7) for an explanation of how sex and gender can be considered)), a region (e.g. rural area, town or city) or even an entire country. These aspects of **population health** at different levels will be examined further in Section 1.3. Working in the public health field means examining the 'bigger picture': identifying a point or points of action to promote a healthy lifestyle, prevent diseases, manage outbreaks, or work at a national level to improve health systems. A **health system** comprises all the health organisations in a country, including the health workforce and their efforts to deliver health services to that population. For instance, in the UK, the health system is represented by the National Health Service (NHS) with its associated commissioning groups, general practitioners, specialists, hospitals, community services, social care providers, pharmacies and public health campaigns. The devolved governments in Wales, Northern Ireland and Scotland organise and fund their own NHS services. However, there are also private health providers. Health systems differ internationally as they rely heavily on health financing and human resources in terms of training and availability. The major concepts in public health action can be divided into three pillars of public health: protection, prevention and promotion. Specifically: - - - Each of these pillars will be examined in detail with a focus on infectious diseases in Topic 5 of this module, but we introduce them in the next section. ### 1.2.1 The three pillars of public health Start of Box **Key information: The pillars of public health** Wherever you see key information boxes in this module, use them to make notes for your revision. This box includes key information about the three pillars of public health, which are central to this module's content. A suggested activity to test your knowledge throughout the module is to think about how each section in the module can be linked to one or more of these three pillars. Health protection is concerned with managing threats and hazards to population health, such as infectious disease outbreaks and the impact of natural disasters or environmental hazards. Health protection includes proactive approaches to prevent outbreaks if the disease is known, such as in the case of tuberculosis, and reactive approaches in cases of **emerging infectious diseases** (an emerging infectious disease can be either an outbreak of a new disease, or a known disease that is expanding in either the number of new cases or in its geographical range). This aspect of public health is a major area for public health practitioners who work in outbreak investigations, such as epidemiologists. Disease prevention is the aspect of public health that focuses on preventing the occurrence of diseases or limiting their complications. It includes activities such as vaccination, screening, and community-based work such as outreach activities carried out by health workers to engage local communities with health education or vaccination programmes. Health promotion is concerned with improving the overall wellbeing of a population by enabling people to take control of their health and make well-informed health choices. Thus, it covers activities such as making healthier lifestyle choices, improving living conditions, addressing health inequalities, plus any factors that are required to achieve a state of physical, mental and social wellbeing. End of Box A major part of public health practice is to examine disease occurrence and trends. To do this requires accurate, timely and relevant data, which can be used to identify risk factors, plan interventions and evaluate population health outcomes. This is mainly studied under the **epidemiology** of diseases (Topic 4). However, public health does not rely on statistics alone. Public health interventions are also informed by an understanding of the biology of a disease and how it spreads, along with psychological theories of human behavioural changes in response to disease outbreaks. Public health also examines the **determinants of health** -- the social, economic and environmental factors which influence people's mental and physical health -- that can result in inequalities between the healthcare of individuals, groups or entire populations (Topic 4). **Environmental health** is an area which examines how environmental factors can affect health. These can be immediate environmental factors, such as living conditions, circumstances following natural disasters or conflict, or issues at the global level, such as climate change. Work through the slides in Figure 1.1 to learn how each of these areas of public health practice fit within the three pillars of public health. Start of Media Content []{#Session4_MediaContent2.anchor}Interactive content is not available in this format. **Figure 1.1 (interactive)** The three pillars in public health: health protection, disease prevention and health promotion. The figure is informed by the World Federation of Public Health Associations (2012) and Thorpe *et al.* (2008). [View description - Figure 1.1 (interactive) The three pillars in public health: health protection, \...](#figure-1.1-interactive-the-three-pillars-in-public-health-health-protection-disease-prevention-and-health-promotion.-the-figure-is-informed-by-the-world-federation-of-public-health-associations-2012-and-thorpe-et-al.-2008.) End of Media Content Start of ITQ - - End of ITQ The bigger picture can be improved by understanding the scientific basis of diseases, and by carrying out a **population health needs assessment** to prioritise the most suitable approach in public health for that specific population. ### 1.2.2 External factors affecting public health decisions The three pillars of public health can be viewed as guiding concepts for public health action. These pillars are not separate and there are several examples of healthcare practice that overlap between the categories. One overlap is between prevention and promotion: when health education leads to behaviour change. For example, in the cases of preventing spread of an infectious disease by promoting correct handwashing techniques, or changing people's attitudes to vaccination using health promotion campaigns. A second overlap is between disease prevention and health protection. For example, routine vaccination is a prevention strategy, but mass vaccination during outbreaks is also a protection strategy. A third overlap is between health protection and promotion. For example, regulations to address environmental hazards are part of health protection, but working at an individual level to promote healthier living conditions is under health promotion. Figure 1.2 demonstrates broadly the three pillars of public health that you saw in Figure 1.1, but now also shows the overlap between these with examples. The core overlap of all three pillars is the use of epidemiology, biostatistics and clinical trials to inform decisions and to understand if they are working as intended (Topic 4). At a wider level than the three pillars, it is acknowledged that improving population health cannot be achieved without considering external factors that can potentially either worsen or improve health outcomes. These factors can be categorised into four main functions: *information*, *capacity*, *advocacy* and *governance*. These can be seen as the external circle of influencers affecting the three pillars in Figure 1.2. Public health decisions must be evidence-based. Hence, the availability and use of information is a major external influence in public health practice, which includes research evidence, surveillance data on current levels of diseases to monitor trends and detect new outbreaks, and monitoring of the determinants of health. Research, evidence and innovation allow consistent improvement in all aspects of the health system. Capacity building is an external influence relating to the infrastructure and health workforce in a health system. **Health systems** collectively include the organisations, institutions and the resources involved in healthcare services, including services in health promotion. In the context of infectious diseases, vaccination and eradication programmes rely on health systems, specifically the health workforce and access to healthcare. These vaccination programmes are also responsible for the logistics involved to ensure the proper and safe distribution of vaccines in a temperature-controlled environment, from the point of production to local vaccination centres. Another external influencer of public health is **advocacy**, which is the strategic effort by different organisations and voluntary groups to raise awareness of a health issue and familiarise the public with it. Part of advocacy action is to ensure that public health practice is ethical with careful communication with the public to promote equity. Public health governance includes public health regulations, economics and policy. **Governance** is required to make evidence-based decisions to ensure that both outbreak management and disease prevention activities are carried out effectively. **Health policy** is defined as the regulations, decisions and actions which have an impact on health spending and the organisation of health delivery. Policy in public health can be national or international. Start of Media Content []{#Session4_MediaContent3.anchor}Interactive content is not available in this format. **Figure 1.2 (interactive)** The three pillars in public health: health protection, disease prevention and health promotion. These pillars have different areas of activity but they also overlap. The areas of overlap depend on the goals of each public health intervention. The areas of overlap in this figure are examples and many more exist. The pillars are also influenced by external influencers: governance, information, capacity and advocacy. [View description - Figure 1.2 (interactive) The three pillars in public health: health protection, \...](#figure-1.2-interactive-the-three-pillars-in-public-health-health-protection-disease-prevention-and-health-promotion.-these-pillars-have-different-areas-of-activity-but-they-also-overlap.-the-areas-of-overlap-depend-on-the-goals-of-each-public-health-intervention.-the-areas-of-overlap-in-this-figure-are-examples-and-many-more-exist.-the-pillars-are-also-influenced-by-external-influencers-governance-information-capacity-and-advocacy.) End of Media Content Start of ITQ - - End of ITQ ### 1.2.3 How to assess the health needs of a population Public health practice is not a 'one-size-fits-all' approach; it is often customised to the needs of different population groups. Understanding the health needs of a population, including sub-groups and communities, is a pivotal step before making important governmental decisions to improve healthcare. A population health needs assessment is a systematic method to review health issues in a population and analyse epidemiological evidence of health outcomes in this population. This process is usually led by government agencies and public health research organisations. They gather information by studying data from national and local sources or by conducting new research to get a clear picture of the population's health needs. Health needs are classified into three main categories: 1. 2. 3. Each of these three categories is taken into consideration and is determined to be either 'met' or 'unmet' as part of the population health needs assessment. An effective health needs assessment ideally ensures that normative needs adequately reflect felt and expressed needs. In every case, the decisions need to be supported by scientific evidence, either from laboratory studies or epidemiological data from how an intervention is working in the community. The intended outcomes from a population health needs assessment in the short term are to prioritise goals, plan resource allocation and improve services. In the longer term, the aim is to reduce health inequalities between populations. To carry out population health needs assessment, a general framework is to follow five steps: 1. 2. 3. 4. 5. ### 1.2.4 Population health needs assessment for TB A practical example of this is tuberculosis (TB) in the UK. In this example, the total number of TB cases is reported followed by the rate per 100 000 to correct for population size. 1. Start of Figure []{#Session4_Figure1.anchor}![Displayed image](media/image2.png) **Figure 1.3** Number of reported cases of TB in the UK from 1971 to 2021 shown as a bar graph with the number of TB cases in 2021 shown as a dotted line, both using the left *y*-axis. The rate of TB (per 100 000) from 1971 to 2021 is shown as a red line using the right *y*-axis (UK Health Security Agency, 2023b). [View description - Figure 1.3 Number of reported cases of TB in the UK from 1971 to 2021 shown as a \...](#figure-1.3-number-of-reported-cases-of-tb-in-the-uk-from-1971-to-2021-shown-as-a-bar-graph-with-the-number-of-tb-cases-in-2021-shown-as-a-dotted-line-both-using-the-left-y-axis.-the-rate-of-tb-per-100-000-from-1971-to-2021-is-shown-as-a-red-line-using-the-right-y-axis-uk-health-security-agency-2023b.) End of Figure Start of ITQ - - End of ITQ 1. Start of Figure []{#Session4_Figure2.anchor}Displayed image **Figure 1.4** Populations at risk of TB in different areas of the UK. [View description - Figure 1.4 Populations at risk of TB in different areas of the UK.](#figure-1.4-populations-at-risk-of-tb-in-different-areas-of-the-uk.) End of Figure Start of ITQ - - End of ITQ 1. Start of ITQ - - End of ITQ 1. 2. Start of Table **Table 1.1** Examples from the *Tuberculosis (TB): action plan for England (2021 to 2026)* (UK Health Security Agency, 2023a). +-----------------+-----------------+-----------------+-----------------+ | **Action** | **Outcome and | **Key | **Main public | | | indicators** | stakeholders** | health pillar** | +=================+=================+=================+=================+ | Maintain the | Monthly and | - - - | Health | | multi-agency | annual reports | | protection | | work among | on TB incidence | | | | UKHSA regions | and trends in | | | | and TB control | TB data | | | | boards. Monitor | | | | | TB | | | | | notifications, | | | | | rates and | | | | | trends, monthly | | | | | and annually, | | | | | locally, | | | | | regionally and | | | | | nationally | | | | +-----------------+-----------------+-----------------+-----------------+ | Optimise the | Commencing | - - | Disease | | BCG vaccine | September 2021, | | prevention | | provision and | monitor and | | | | support BCG | report annually | | | | programme | on BCG uptake | | | | change to | in those | | | | vaccinate at 4 | eligible by the | | | | weeks old | following | | | | | indicators: | | | | | | | | | | a. b. | | | +-----------------+-----------------+-----------------+-----------------+ | Encourage use | Report annually | - - | Health | | of new tools | on new tools | | promotion | | such as digital | and their use | | | | and social | to raise | | | | media to raise | awareness in | | | | awareness of TB | at-risk | | | | in at-risk | populations and | | | | populations and | healthcare | | | | healthcare | workers | | | | workers | | | | +-----------------+-----------------+-----------------+-----------------+ End of Table These examples can be added to a Venn diagram like the one in Figure 1.2 to provide an overall summary of how health protection, disease prevention and health promotion are addressed in the UK by the *Tuberculosis (TB): action plan for England (2021 to 2026)* strategy. Start of ITQ - End of ITQ Work through the slideshow in Figure 1.6, which shows examples from the *Tuberculosis (TB): action plan for England (2021 to 2026)* placed under the three pillars of public health in the same Venn diagram. Start of Media Content []{#Session4_MediaContent5.anchor}Interactive content is not available in this format. **Figure 1.6 (interactive)** Slideshow showing how examples from the *Tuberculosis (TB): action plan for England (2021 to 2026)* relate to the three pillars of public health. [View description - Figure 1.6 (interactive) Slideshow showing how examples from the Tuberculosis (TB): \...](#figure-1.6-interactive-slideshow-showing-how-examples-from-the-tuberculosis-tb-action-plan-for-england-2021-to-2026-relate-to-the-three-pillars-of-public-health.) End of Media Content Start of ITQ - - End of ITQ Start of ITQ - - End of ITQ 1.3 People, places and stages of life -------------------------------------- Public health efforts are organised to focus on improving health outcomes by addressing the unique needs of different people living in different places, and throughout different stages of life. This approach can be thought of as a conceptual framework in public health programmes. It is relevant to **descriptive epidemiology** (Topic 4) and provides the scientific grounds to identify and tackle inequalities. Improving health outcomes requires taking the health needs of a group or a population into consideration. Such needs might be different based on demographic factors, for example, age. Thus, children are vulnerable to a specific set of 'childhood' diseases, while older age groups often have **co-morbidities**, such as cardiovascular or endocrine diseases, that can worsen the outcome of an infectious disease. Campaigns to increase awareness of vaccine-preventable childhood diseases ideally target parents and guardians. Other demographic factors, such as biological sex, gender or ethnic differences, can also influence health and will be discussed in more detail when you learn about the determinants of health in Topic 4. Start of Example **Example: People factors** Ebola is a serious viral disease that is often fatal; it kills 25--90% of those infected, which makes preventing its spread crucial. It was first recorded in 1976 near the Ebola river in the Democratic Republic of Congo (DRC) and since then there have been several outbreaks. Ebola virus spreads via direct contact with body fluids from infected individuals or objects contaminated with infected body fluids. Cultural practices in the DRC in caring for the patients and in funerals increase the risk of transmission. A public health intervention could therefore focus on the people factor by providing health education to communities on how certain kinds of funeral practices risk further infection and how such practices must change during outbreaks. The intervention also includes training healthcare professionals on caring for infected individuals. End of Example **Place** is another factor in public health practice. Place factors include the physical environment at an immediate level, such as living and working conditions, and wider environmental influences. Place factors also include the social and economic dimensions of the place, such as the availability of healthy food, access to transport, and access to green spaces or places for exercise. Start of Example **Example: Place factors** In 2020, the WHO reported differences in the under-five mortality rate within some low- and middle-income countries (**LMICs**). For context, the global average under-five mortality rate that year was 39 deaths per 1000 live births. In one third of LMICs studied, the under-five mortality rate was 20 deaths per 1000 live births higher in rural areas than in urban areas. Consider Rwanda as an example to illustrate this difference. The under-five mortality rate in Rwanda was 52.6 per 1000 live births in rural areas compared to 35.5 per 1000 live births in urban areas. These data highlighted a pressing need to target more vaccination campaigns to rural areas in Rwanda. End of Example The **stages of life** represent the different phases of human life, from infancy to old age. As a person goes through these stages, their health needs change. For example, health status and living circumstances change with age. Together these are all recognised under the stages of life concept. Start of Example **Example: Stage of life factors** In early childhood, there is a set of routine vaccinations to prevent under-five child mortality. Typically, these vaccines protect against: rotaviruses, meningococcal B bacteria, pneumococcal bacteria, diphtheria, hepatitis B, polio, tetanus, whooping cough, measles, mumps, rubella, and *Haemophilus influenzae* type b. Figure 1.7a is an example of an NHS flyer to promote measles vaccination for children in the UK. In early adolescence, human papillomavirus (HPV) vaccination is recommended to prevent the sexual transmission of HPV, which can cause genital warts and cancers. In adulthood, the influenza vaccine is recommended each year, especially for older age groups and individuals with chronic conditions such as diabetes and chronic obstructive pulmonary disease. Figure 1.7b is an example of an NHS flyer in the UK that promotes flu vaccination in winter for adults. Start of Figure []{#Session4_Figure3.anchor}![Displayed image](media/image4.jpg) **Figure 1.7** (a) NHS flyer for the measles vaccination. [View description - Figure 1.7 (a) NHS flyer for the measles vaccination.](#figure-1.7-a-nhs-flyer-for-the-measles-vaccination.) End of Figure Start of Figure []{#Session4_Figure4.anchor}Displayed image **Figure 1.7** (b) NHS flyer for the flu vaccination. [View description - Figure 1.7 (b) NHS flyer for the flu vaccination.](#figure-1.7-b-nhs-flyer-for-the-flu-vaccination.) End of Figure Campaigns that target vaccinations at different stages of life also take into consideration the people and places factors. Figure 1.8 shows a selection of polio vaccination flyers from different countries. You will note that all flyers target the same stage of life and the same disease, but the targeted audience are different people in different places, hence each design is tailored to be more appropriate for these populations in terms of demographics, culture and sometimes, language. Start of Figure []{#Session4_Figure5.anchor}![Displayed image](media/image6.png) **Figure 1.8** Polio vaccination flyers from different countries (including HIC, LMIC and LICs). [View description - Figure 1.8 Polio vaccination flyers from different countries (including HIC, LMIC \...](#figure-1.8-polio-vaccination-flyers-from-different-countries-including-hic-lmic-and-lics.) End of Figure End of Example Start of Activity **Activity 1.2 Planning public health interventions** You should allow approximately 30 minutes for this activity. Spend about 15 minutes on each part. Start of Question This activity will help you to achieve [learning outcome 1.1](#learningoutcomes). It also develops the employability skills of communication, collaboration, and digital and information literacy. End of Question []{#Session4_Part4.anchor}Start of Question Global health statistics reveal that during 2014--2019, only 60% of births in sub-Saharan Africa were assisted by skilled health personnel, increasing the risk of maternal mortality. The underlying factors include issues in access to healthcare for women, the availability of trained health personnel and the overall quality of care, such as infection control strategies. Accordingly, 66% of global maternal deaths occurred in sub-Saharan Africa during this reporting period, most of which were due to an infection acquired during or soon after birth. 1. Start of Media Content Interactive content is not available in this format. End of Media Content End of Question [View answer - Part](#answer) Start of Question 1. Start of Media Content Interactive content is not available in this format. End of Media Content In the Planning a public health intervention discussion in your tutor group forum, post the intervention you found and compare your intervention with those other students have found. In your comparison focus on: - - You will probably find that the same health issue can be tackled by interventions focused on preventive measures, strategies for health protection or health promotion activities. You will also find that all interventions are tailored to people, places and stage of life concepts. End of Question End of Activity 1.4 The global scale of death from infectious diseases ------------------------------------------------------- At the time of writing (2023), the most recent global death statistics related to 2019 when a total of 7.8 million people died due to infectious diseases. Although these numbers may sound shocking, they represent only 14% of the total deaths that year (55.4 million deaths); larger proportions of total deaths were due to cardiovascular diseases (17.9 million) and cancers (9.3 million). In contrast, there were nearly 138 million births globally in 2019, roughly 2.5 times more than the number of deaths that year. Start of Activity **Activity 1.3 Exploring global health data** You should allow approximately 15 minutes for this activity. Start of Question This activity will help you to achieve [learning outcome 1.3](#learningoutcomes). It also develops the employability skills of numeracy and digital and information literacy. End of Question Start of Question You are going to explore these data for yourself using the Global Health Data Explorer on the Our World in Data website. First watch Video 1.1 to learn how to navigate the website. Start of Media Content []{#Session4_MediaContent8.anchor}Video content is not available in this format. **Video 1.1** How to navigate the Global Health Data Explorer tool on Our World in Data [View transcript - Video 1.1 How to navigate the Global Health Data Explorer tool on Our World in \...](#video-1.1-how-to-navigate-the-global-health-data-explorer-tool-on-our-world-in-data) End of Media Content Once you have watched the video, click on the link and follow the instructions below. [Global Health Data Explorer -- Our World in Data](https://www.open.ac.uk/libraryservices/resource/website:152835&f=37143) The Global Health Data Explorer webpage can be set to show many different aspects of health by changing the options at the top of the webpage. Initially, you should find it is set to show the number of deaths due to all infectious diseases. At the bottom of the webpage, you can choose different ways to visualise these data: as a timeline chart, a global map or a table of different countries. End of Question []{#Session4_Part8.anchor}Start of Question Hover your pointer over a country and you should see a graph of deaths over time. Do this for several of the countries and describe the general trend. End of Question [View answer - Part](#answer-1) End of Activity There are many ways to quantify death statistics. Figure 1.9 shows the total number of deaths due to infectious diseases in each country in 2019. The figure suggests that infectious disease deaths in 2019 were broadly spread across the globe, with hotspots in India (1.84 million deaths) and Nigeria (813 687 deaths), and a large discrepancy between the US (108 744 deaths) and Canada (11 861 deaths). But viewing these data alone can be misleading. Start of Figure []{#Session4_Figure6.anchor}Displayed image **Figure 1.9** Deaths from infectious diseases in 2019. [View description - Figure 1.9 Deaths from infectious diseases in 2019.](#figure-1.9-deaths-from-infectious-diseases-in-2019.) End of Figure It is obvious that data based on total deaths exaggerate the contribution from countries with larger populations. So, somewhere like the US, with a relatively advanced healthcare system, sits in the category of 100 000 to 500 000 deaths due to infectious diseases. This is over nine times more deaths than Canada, with a similarly advanced healthcare system. If instead the data are corrected for population size by dividing by the number of people in each country (i.e. **per capita**), then a different situation is revealed. In Figure 1.10 the same data are now shown as the death rate per 100 000 people (this is the per capita rate, multiplied by 100 000). You will learn more about interpreting disease statistics in Section 1.5. Start of Figure []{#Session4_Figure7.anchor}![Displayed image](media/image8.png) **Figure 1.10** Death rate per 100 000 people from infectious diseases in 2019. [View description - Figure 1.10 Death rate per 100 000 people from infectious diseases in 2019.](#figure-1.10-death-rate-per-100-000-people-from-infectious-diseases-in-2019.) End of Figure Compare Figures 1.9 and 1.10. Notice how by standardising each country to per capita values, the apparent death discrepancy between the US and Canada you saw in Figure 1.9 has disappeared. The per capita deaths in the US were 33.2 per 100 000 people compared with 32.5 per 100 000 people in Canada. Notice also that India and Nigeria are not the hotspots for infectious disease deaths that the raw death numbers suggested (although they are both high). Instead, almost all of sub-Saharan Africa has the highest rates of infectious diseases per capita, ranging from around 200--500 deaths per 100 000 people. ### 1.4.1 Exploring variations in death rates In general, the countries with the highest infectious disease rates include regions where the climate naturally favours the survival of infectious agents which cause the disease, or animals that can transmit them to people (e.g. biting arthropods such as mosquitoes). Start of Box Infectious diseases that are regularly found in a particular region or in a particular group of people are called **endemic**. End of Box Moreover, lifestyle and farming practices in many of these countries involve people living and working closely with nature and domesticated animals, making it easier for diseases to pass between animals and humans. Start of Activity []{#Session4_Activity4.anchor}**Activity 1.4 Global health data trends** You should allow approximately 5 minutes for this activity. Start of Question This activity will help you to achieve [learning outcome 1.3](#learningoutcomes). It also develops the employability skills of numeracy and digital and information literacy. Return to the website [Global Health Data Explorer -- Our World in Data](https://www.open.ac.uk/libraryservices/resource/website:152835&f=37143) Just as you did in Activity 1.3, hover your pointer over individual countries and notice the trends in infectious disease death rates over time, and use this information to answer the question below. (At the time of writing (2023), the range of values displayed was from 1990--2019.) What is the general trend in death rates due to infectious disease over the past 30 years? Is the same trend seen in most sub-Saharan African countries? If not, describe the trend in these countries. End of Question [View answer - Activity 1.4 Global health data trends](#answer-2) End of Activity Several of the countries with high infectious disease death rates also suffer from a shortage of money to spend on infrastructure, disease surveillance programmes and healthcare (Figure 1.11). Start of Figure []{#Session4_Figure8.anchor}Displayed image **Figure 1.11** Public health expenditure as a share percentage of GDP in 2019. [View description - Figure 1.11 Public health expenditure as a share percentage of GDP in 2019.](#figure-1.11-public-health-expenditure-as-a-share-percentage-of-gdp-in-2019.) End of Figure Start of Box **Surveillance programmes** involve the collection, analysis, and interpretation of disease statistics to better understand the effectiveness and help optimise the delivery of disease control and prevention measures. End of Box Moreover, there are differences in the coverage of essential healthcare within individual healthcare systems (Figure 1.12), and the priorities they are focused on. All these differences are compounded in some cases by political instability, corruption, conflict, climate change, and shortages of food or water. However, in many of the currently low-ranked countries, the trends in the coverage of essential health services show consistent improvements, while many high-income countries have largely plateaued. The reasons for this are complex, but one simple reason is that because of better funding in HICs, many of the straightforward improvements that can be made to health services have already been done. While in lower-income countries, as funds become available, these improvements are still ongoing. Start of Figure []{#Session4_Figure9.anchor}![Displayed image](media/image10.png) **Figure 1.12** Quality and accessibility of the healthcare provision in 2019. The scale is based on a range of factors including healthcare quality, access to healthcare and death rates. The higher the number, the better. [View description - Figure 1.12 Quality and accessibility of the healthcare provision in 2019. The scale \...](#figure-1.12-quality-and-accessibility-of-the-healthcare-provision-in-2019.-the-scale-is-based-on-a-range-of-factors-including-healthcare-quality-access-to-healthcare-and-death-rates.-the-higher-the-number-the-better.) End of Figure Start of ITQ - - End of ITQ In summary, it is important to realise that public health approaches to combatting infectious diseases are rarely just about the biological control of the causative infectious agent. Instead, effective and long-lasting public health strategies require a holistic approach that tackles the factors affecting the health of individuals and communities, known as *determinants of health*. You will learn more about the determinants of health in Topic 4. 1.5 Burden of disease ---------------------- Although several diseases can be fatal or life-limiting, many more result in long-term health problems that can not only cause suffering to the affected individuals and their families, but also have a huge impact on domestic and national economies and healthcare services. To capture information about the overall health impact of a disease on a population, health agencies and governments often talk in broader terms about the **burden of disease**, a statistic that encompasses both deaths (**mortality**) and suffering (**morbidity**). Specifically, the burden of a disease is quantified as disability-adjusted life years (**DALYs**), where one DALY represents the loss of one year of full health due to the disease. DALYs are the sum of two components: the *mortality* component is quantified as the years of life lost due to premature mortality (**YLL**), and the *morbidity* component is quantified as the years lived with disability (**YLD**). Because one disease can sometimes increase susceptibility to other diseases or conditions, the YLD component also takes any of these co-morbidities into account. It is important to realise that the YLL value is not the same thing as the number of deaths. Instead, it is a measure of the years of life lost (effectively 'stolen' by that disease). The YLL assumes a standard, average lifespan for each person. Therefore, for the same disease, if it killed a young person, it would rob them of more of that average lifespan and produce a higher YLL value, compared with if it killed an older person (nearer to the end of the average lifespan and thus only robbing them of a few years of their life). Video 1.2 explains how DALYs are calculated. Start of Media Content []{#Session4_MediaContent9.anchor}Video content is not available in this format. **Video 1.2** How DALYs are calculated. [View transcript - Video 1.2 How DALYs are calculated.](#video-1.2-how-dalys-are-calculated.) End of Media Content In Figure 1.13a, the DALYs per 100 000 people are shown for TB in six different regions of the world for the year 2019. The purpose of this graph is to get you used to seeing DALYs presented as a stacked bar, in which the overall size of the bar is the DALY, separated into the disability component (YLD) at the bottom and the premature mortality component (YLL) at the top. Figure 1.13b is a map showing the six different global regions referred to in the graph. In the next section, you will examine these graphs in more detail and for a broader range of infectious diseases. Start of Figure []{#Session4_Figure10.anchor}Displayed image **Figure 1.13** (a) Stacked bar charts of DALYs for tuberculosis in each of the six WHO global regions. Each bar is subdivided into the disability (YLD, lower portion of bar) and mortality (YLL, upper portion of bar) components of the DALY. [View description - Figure 1.13 (a) Stacked bar charts of DALYs for tuberculosis in each of the six \...](#figure-1.13-a-stacked-bar-charts-of-dalys-for-tuberculosis-in-each-of-the-six-who-global-regions.-each-bar-is-subdivided-into-the-disability-yld-lower-portion-of-bar-and-mortality-yll-upper-portion-of-bar-components-of-the-daly.) End of Figure Start of Figure []{#Session4_Figure11.anchor}![Displayed image](media/image12.png) **Figure 1.13** (b) Map showing the six WHO global regions. [View description - Figure 1.13 (b) Map showing the six WHO global regions.](#figure-1.13-b-map-showing-the-six-who-global-regions.) End of Figure ### 1.5.1 Factors affecting the burden of disease Let's now look at a broader range of diseases within the same six global regions during 2019, as in Figure 1.13, and identify some trends. Figure 1.14 shows the DALYs for five major diseases: tuberculosis, HIV/AIDS, diarrhoeal diseases, malaria, and lower respiratory infections. Start of Figure []{#Session4_Figure12.anchor}Displayed image **Figure 1.14** Stacked bar charts of DALYs per 100 000 people for five major communicable diseases in 2019 (tuberculosis, HIV/AIDS, diarrhoeal diseases, malaria, and lower respiratory infections), in each of the six WHO global regions. Each bar is subdivided into the disability (YLD, lower portion of bar) and mortality (YLL, upper portion of bar) components of the DALY. [View description - Figure 1.14 Stacked bar charts of DALYs per 100 000 people for five major communicable \...](#figure-1.14-stacked-bar-charts-of-dalys-per-100-000-people-for-five-major-communicable-diseases-in-2019-tuberculosis-hivaids-diarrhoeal-diseases-malaria-and-lower-respiratory-infections-in-each-of-the-six-who-global-regions.-each-bar-is-subdivided-into-the-disability-yld-lower-portion-of-bar-and-mortality-yll-upper-portion-of-bar-components-of-the-daly.) End of Figure There are several interesting points to notice in Figure 1.14. Start of ITQ - - - - End of ITQ Let's investigate each of those trends in more detail: - Recall that the YLL figure is years of life *lost* due to disease and therefore has an age component built into it. YLL compares the age of death with an average lifespan to calculate how many years a person has been 'cheated of' by death. Therefore, in addition to the overall number of deaths, diseases that predominantly kill infants and young people, such as lower respiratory diseases, make a greater contribution to YLL than a disease that mainly affects older people. - This observation implies these diseases kill quickly and/or resolve without long-term health implications. Certainly, respiratory diseases can be deadly. Pneumonia, for instance, is the leading cause of death in children under five years of age, responsible for 15% of all childhood deaths. At the other end of the age spectrum, pneumonia kills 30% of hospitalised patients older than 75 years of age. Surprisingly, pneumonia rarely results in long-term lung damage, but the lack of oxygen during infection puts a strain on many other organs and can leave people susceptible to stroke and heart disease for several years, making it difficult to attribute death from these causes to a prior lower respiratory infection. - While the reasons for this are complex, other contributing factors include the high levels of malnutrition in sub-Saharan Africa that you will learn about next, combined with the low funding for healthcare (Figure 1.11), and subsequent poor quality and access to healthcare (Figure 1.12) that you have already seen. #### Malnutrition As with many infectious diseases, the group of countries that constitute the Global South also have the highest levels of malnutrition (Figure 1.15). Start of Figure []{#Session4_Figure13.anchor}![Displayed image](media/image14.png) **Figure 1.15** Prevalence of malnutrition in the world, 2019--2021 (FAO, 2022; WHO *et al*., 2022). [View description - Figure 1.15 Prevalence of malnutrition in the world, 2019--2021 (FAO, 2022; WHO et \...](#figure-1.15-prevalence-of-malnutrition-in-the-world-20192021-fao-2022-who-et-al.-2022.) End of Figure At least two factors combine to cause high levels of malnutrition in sub-Saharan Africa. - - Watch Video 1.3 from the Belgian non-governmental organisation, SOS Faim, which fights against hunger and poverty in Africa, and Central and South America. Although the video was made in 2012, it is still relevant today since very little has changed. Start of Media Content **Video 1.3** The paradox of hunger in the world. End of Media Content #### Consequences of malnutrition Malnutrition reduces the ability of the body to fight off infections, so it seems obvious that populations with high levels of malnutrition will be more susceptible to infectious diseases. Additionally, the relationship between malnutrition and disease often involves a vicious cycle. For instance, repeated diarrhoeal infections cause chronic damage to the gut, reducing its ability to absorb nutrients and destabilising the gut microbiome that helps regulate the immune system and protect the gut from infection. Consequently, each episode of a diarrhoeal disease worsens malnutrition, and makes people more susceptible to subsequent diarrhoeal diseases and further dehydration. Similarly, in a study of the burden of disease in 195 countries between 1990 and 2016, malnutrition was found to be the leading factor in around 60% of lower respiratory infection deaths in children (GBD, 2018). Start of Activity **Activity 1.5 Current global infectious disease threats** You should allow approximately 15 minutes for this activity. Start of Question This activity will help you to achieve [learning outcome 1.2](#learningoutcomes). It also develops the employability skills of communication, collaboration and initiative. Your contributions to this activity will be assessed in TMA 01. Go to the [Current global infectious disease threat poll wiki](https://learn2.open.ac.uk/mod/oucontent/olinkremote.php?website=SK297&targetdoc=Current%20global%20infectious%20disease%20threat%20poll) in the Topic 1 section of the study planner. Edit the wiki to add what you think is the leading current global infectious disease threat. If someone has already listed it then edit the table to add another number to the total tally. In the Current global infectious disease threats discussion in your tutor group forum, discuss why you think these are the greatest health threats. You might have different answers to the others in your group because you are thinking about different reasons that can make a pathogen a global threat. This discussion will also get you thinking about what a perfect pathogen might be, which you will look at in more detail in Topic 2. End of Question End of Activity ### 1.5.2 LMICs and HICs Start of Box **Key information: Categorising countries** The old terminology of 'developing' and 'developed' countries is no longer used. 'Developing' implied poverty, an undeveloped industrial base, low education and life expectancy, not all of which necessarily co-existed. Conversely, 'developed' suggested near perfection, which is certainly not true in many cases. Instead, countries are now categorised according to their **gross national income** (GNI) or **gross domestic product** (GDP). There is a subtle difference between these two values, but they both measure aspects relating to the wealth of a country. GNI is the total income received by a country from its residents and businesses, regardless of whether they are located in the country or abroad. GDP is the total market value of all goods and services produced within the country. Dividing either of these values by the total population of the country gives an idea of the money available per person (per capita), and these GNI per capita or GDP per capita values are therefore used to compare countries, in a similar way to how health statistics are converted into per capita values to allow comparisons. Thus, most countries that used to be categorised as 'developing' are now referred to as either low-income countries (LICs) or lower-middle-income countries (LMICs). This avoids creating the false impression that everything about these countries is 'not yet developed'. Similarly, countries that were previously referred to in some literature as 'developed' are now either called upper-middle-income countries (UMICs) or high-income countries (HICs), and again, just because they have more money per capita than some other countries this in no way implies that everything about them is good or they are somehow 'better' than countries with a lower GDP/GNI per capita. Each year, the World Bank sets the threshold GNI per capita values for defining low to high income countries. Table 1.2 shows the GNI per capita bands (in US dollars) for 2022. Start of Table **Table 1.2 **World Bank GNI per capita values for defining low to high income countries. **Income band** **GNI per capita** --------------------- -------------------- low income \$1 085 or below lower-middle income \$1 086--\$4 225 upper-middle income \$4 256--\$12 205 high income \$13 205 or above End of Table End of Box The leading causes of death are different in HICs and LICs. Figure 1.16a shows that the leading causes of death in HICs in 2019 were non-communicable diseases, such as heart disease, dementia, stroke, cancer and diabetes. There are at least two reasons for this: 1. 2. By contrast, in LICs, deaths in 2019 were mainly due to neonatal conditions and respiratory infections, with infectious diseases contributing a much higher proportion of deaths overall (Figure 1.16b). Start of Figure []{#Session4_Figure14.anchor}Displayed image **Figure 1.16** (a) Leading causes of death in all high-income countries. [View description - Figure 1.16 (a) Leading causes of death in all high-income countries.](#figure-1.16-a-leading-causes-of-death-in-all-high-income-countries.) End of Figure Start of Figure []{#Session4_Figure15.anchor}![Displayed image](media/image16.png) **Figure 1.16** (b) Leading causes of death in all low-income countries. [View description - Figure 1.16 (b) Leading causes of death in all low-income countries.](#figure-1.16-b-leading-causes-of-death-in-all-low-income-countries.) End of Figure ### 1.5.3 How GDP impacts life expectancy GDP per capita is an indicator of average wages and average living standards. A higher GDP per capita implies wider access to factors such as better quality and quantity of food, sanitation, housing, education, and healthcare systems. Unsurprisingly therefore, population health generally increases with GDP per capita. Of course, the GDP per capita figure gives no information on how the money is spread between citizens, so it is still possible to have two countries with identical GDP per capita, but differences in health because of inequalities in accessing many of the factors listed above. The chart in Figure 1.17 plots the GDP per capita against the life expectancy at birth in 2018 for several countries. Each country is shown as a circle and the size of the circle gives an indication of their population. The chart is interactive; you can change the GDP per capita scale (on the *x*-axis) to be either linear or logarithmic (log~2~) by moving between the two slides. The log scale has the effect of spreading out the lower income countries on the chart. Start of Media Content []{#Session4_MediaContent11.anchor}Interactive content is not available in this format. **Figure 1.17 (interactive)** Life expectancy vs. GDP per capita, 2018. GDP has been split into three shaded sections: lower (LICs plus LMICs), middle (UMICs), and high (HICs). Select the 'linear' button to view the data as a linear graph or the 'logarithmic' button to view the data as a logarithmic graph. [View description - Figure 1.17 (interactive) Life expectancy vs. GDP per capita, 2018. GDP has been \...](#figure-1.17-interactive-life-expectancy-vs.-gdp-per-capita-2018.-gdp-has-been-split-into-three-shaded-sections-lower-lics-plus-lmics-middle-umics-and-high-hics.-select-the-linear-button-to-view-the-data-as-a-linear-graph-or-the-logarithmic-button-to-view-the-data-as-a-logarithmic-graph.) End of Media Content However you choose to view the data in Figure 1.17, there's an obvious positive correlation between life expectancy and the per capita national income of a country -- as GDP per capita goes up, so does life expectancy. However, there are several outliers. For instance, using the log scale, you can see that Equatorial Guinea, Nigeria and Chad have lower life expectancies than their income might predict. Conversely, North Korea has a higher life expectancy than its income might predict. Using either *x*-axis, but especially noticeable using the linear display, Qatar has a huge income, but its life expectancy is not the highest. Countries such as Japan, Australia and Switzerland all have higher life expectancies than Qatar, while the highest life expectancy is Monaco. What's happening with these outliers? The first thing to realise is that the data only show a snapshot from 2018, so these values may change from year to year. To gain a better understanding requires long-term data. Moreover, these data do not discriminate between deaths due to communicable diseases and deaths due to non-communicable diseases. Notwithstanding these limitations, it could be the case that there's an uneven distribution of wealth, such that a small proportion of the population is responsible for most of the national income. Alternatively, external funding agencies or healthcare agencies might be targeting specific diseases in the country that could improve lifespan but would not show up in the national income values. Now complete Activity 1.6 and consider the majority of countries that fall on a more obvious line linking income with life expectancy. Start of Activity []{#Session4_Activity6.anchor}**Activity 1.6 GDP and life expectancy** You should allow approximately 15 minutes for this activity. Start of Question This activity will help you to achieve [learning outcome 1.3](#learningoutcomes). It also develops the employability skills of problem solving and communication. Think of as many reasons as you can to explain how national income affects life expectancy, especially in the context of infectious diseases. End of Question *Provide your answer\...* [View answer - Activity 1.6 GDP and life expectancy](#answer-3) End of Activity ### 1.5.4 How have public health interventions reduced the burden of disease? International health organisations and charities regularly identify regional health issues and address these with targeted campaigns. Examples of some of these interventions are listed in Table 1.3 below, together with an indication of whether they achieved their goals. These include a mixture of interventions that target either infectious diseases or non-communicable diseases. Necessarily, these interventions are quite old now, allowing sufficient time to assess if they achieved their aims or not. You are not expected to recall any details of these health campaigns. Links to further information are included if you would like to find out more about the interventions. Some of these health issues will be covered in more detail in later topics. Start of Table Table 1.3 Examples of health issue interventions. +-------------+-------------+-------------+-------------+-------------+ | **Health | **Years | **Agency | **Intervent | **Indicator | | issue to be | active** | responsible | ion** | s | | addressed** | | ** | | of | | | | | | success** | +=============+=============+=============+=============+=============+ | Preventing | 2007--now | UK | [UK ban on | 25% | | strokes and | | Government | smoking in | decrease in | | cardiovascu | | (The Health | enclosed | tobacco | | lar | | Act 2006) | public | metabolites | | diseases | | | places](htt | in | | due to | | | ps://www.op | non-smokers | | passive | | | en.ac.uk/li | (Robson, | | smoke | | | braryservic | 2021) | | inhalation | | | es/resource | | | (UK) | | | /article:15 | 1200 fewer | | | | | 2836&f=3714 | hospital | | | | | 3) | admissions | | | | | | for heart | | | | | | attacks, | | | | | | one year | | | | | | after the | | | | | | ban (Sims, | | | | | | 2010) | +-------------+-------------+-------------+-------------+-------------+ | Reducing | 2008--now | NHS routine | [Routine | 86% | | the | | vaccination | HPV | decrease in | | incidence | | s | vaccination | HPV in | | of cervical | | | of all | young women | | cancer from | | | 13--16 year | in England. | | human | | | old | 71% | | papillomavi | | | girls](http | reduction | | rus | | | s://www.ope | in | | (HPV) | | | n.ac.uk/lib | pre-cancero | | infection | | | raryservice | us | | (UK) | | | s/resource/ | cervical | | | | | website:152 | disease in | | | | | 837&f=37143 | women in | | | | | ) | Scotland | | | | | | (Saliba, | | | | | | 2018) | | | | | | | | | | | | Estimated | | | | | | prevention | | | | | | of over | | | | | | 64 000 | | | | | | cases | | | | | | ofcervical | | | | | | cancer by | | | | | | 2058 | | | | | | (Public | | | | | | Health | | | | | | England, | | | | | | 2019) | +-------------+-------------+-------------+-------------+-------------+ | Reducing | 2007--2011 | South | [Condom | 60% | | the | | African | distributio | decrease in | | incidence | | government | n | HIV | | of sexually | | | programmes] | prevalence | | transmitted | | | (https://ww | in young | | infections | | | w.open.ac.u | women | | and HIV | | | k/libraryse | (USAID | | (South | | | rvices/reso | factsheet, | | Africa) | | | urce/websit | 2015) | | | | | e:152840&f= | | | | | | 37143) | | +-------------+-------------+-------------+-------------+-------------+ | Guinea worm | 1986--now | Carter | [Guinea | In 1986, | | disease | | Center, | worm | Guinea worm | | | | WHO, UNICEF | eradication | disease | | | | | program via | affected | | | | | community-b | 3.5 million | | | | | ased | people per | | | | | education]( | year in 21 | | | | | https://www | countries | | | | |.open.ac.uk | in Africa | | | | | /libraryser | and Asia. | | | | | vices/resou | By 2022, | | | | | rce/website | this had | | | | | :152841&f=3 | been | | | | | 7143) | reduced to | | | | | | just a | | | | | | handful of | | | | | | cases. A | | | | | | reduction | | | | | | of around | | | | | | 99.99% | | | | | | (Carter | | | | | | Center, | | | | | | 2024) | +-------------+-------------+-------------+-------------+-------------+ End of Table 1.6 What is public health? Revisited ------------------------------------- Start of Activity **Activity 1.1 Part 2 What is public health? Revisited** You should allow approximately 10 minutes for this activity. Start of Question Look again at the words you used to describe the term 'public health' at the start of this topic. Start of Media Content Interactive content is not available in this format. End of Media Content Now that you have understood a little more about what is and is not covered by the term 'public health', use this word cloud to repeat the exercise, and write three or four words that describe what you *now* think public health is concerned with. Start of Media Content Interactive content is not available in this format. End of Media Content End of Question Start of Question Reflect on how your initial ideas about public health have changed. End of Question *Provide your answer\...* Start of Question In the next section, you will see the word cloud that you and the other students filled in at the start of the topic (Activity 1.1 Part 1) and the word cloud you have just filled in (Activity 1.1 Part 2). Review both of these word clouds and decide if you came to the same conclusions as the other students. Did you find any suggestions from the other students to be useful? (Please only do this activity at the end of Part 1. Otherwise, if you have reached this point too soon, there won't be many responses from the other students for you to compare yours with.) End of Question End of Activity ### 1.6.1 Cohort-wide word clouds These are the words you and the other students came up with at the start of the topic (Activity 1.1 Part 1). Start of Media Content Interactive content is not available in this format. End of Media Content These are the words you and the other students came up with just now, after studying Part 1 of the topic (Activity 1.1 Part 2). Start of Media Content Interactive content is not available in this format. End of Media Content Conclusion to Part 1 -------------------- In Part 1, you have been introduced to the three pillars of public health and how they are each used to assess and maintain the public health needs of a population. You also learnt about disease statistics on a country and regional basis (numbers of deaths, per capita deaths and DALYs), and some of the factors that lead to these inequalities in health, mainly poverty and malnutrition. Part 2 Characterising infectious diseases ----------------------------------------- Introduction to Part 2 ---------------------- In this part, you will consider the different ways in which infectious diseases can be categorised. Then you will examine the scale of deaths due to infectious disease each year, noting some of the major killers, and place this in the context of total annual deaths. With your knowledge of some of the factors that can worsen health outcomes from Part 1, you will research and discuss the infectious diseases TB and HIV within your tutor group. Following that, you will learn how an infectious disease can be attributed to a specific infectious agent. Finally, you will investigate how most human infectious diseases originate. 2.1 Characterising infectious diseases --------------------------------------- Part 1 introduced infectious diseases, but what exactly are they? An infectious disease can be passed between individuals, although the exact mechanism of exchange varies from pathogen to pathogen. Transfer from an infected person to an uninfected person can be either direct or indirect. - - Start of Box Note that while droplet and aerosol transmission may sound very similar, droplets are larger and fall to the ground quickly, while aerosols are much smaller and can remain suspended in the air for hours. End of Box We will be looking in detail at all these transmission mechanisms in Topic 2, but for the moment let's focus on what we mean by the term **pathogen** and the global scale of infectious diseases. Any organism or material that causes disease(s) may be referred to as a pathogen or **pathogenic**, from a combination of two ancient Greek words: *pathos*, meaning 'pain' or 'suffering' and *genes*, meaning 'producer of'. However, not all infections cause suffering -- some infections may produce very minor or no symptoms at all (so called **asymptomatic** cases). Thus, a broader term for something that causes a disease is an **infectious agent**. Typically, we think of infectious agents as being living organisms. However, not all infectious agents are 'alive'. They also include pathogens such as viruses and infectious proteins known as prions. (We will discuss whether viruses are living organisms or not in Topic 3, but we do not cover prions in this module.) Start of Activity **Activity 2.1 Part 1 Categorising infections** You should allow approximately 30 minutes for this activity. Start of Question This activity will help you to achieve [learning outcome 1.2](#learningoutcomes). It also develops the employability skill of problem solving. End of Question Start of Question From your own experiences or prior reading, what examples for the following categories of human infectious diseases can you think of? Fill in Table 2.1 with as many as you can. At the end of this part you will see this table again, and will be able to change or add more examples before revealing an answer version for you to compare with. End of Question Start of Question Start of Table Table 2.1 Common categorisations for human infectious diseases. **Categorisation** **Examples** --------------------------------------------- --------------------------- Types of infectious agents *Provide your answer\...* Modes of transmission between humans *Provide your answer\...* Transmission to humans by other vertebrates *Provide your answer\...* Transmission to humans by a vector *Provide your answer\...* Symptoms *Provide your answer\...* Parts of the body affected *Provide your answer\...* Timescales *Provide your answer\...* End of Table End of Question End of Activity 2.2 Signs and symptoms of infectious diseases ---------------------------------------------- In general, diseases can be categorised according to: 1. 2. 3. ### Signs and symptoms **Signs** of a disease are the objective measures that people, such as a doctor, would notice. Some signs are highly specific to a disease, such as pustules, while others, such as a fever or rash, are more generic. **Symptoms** are subjective feelings we associate with 'being ill', such as headaches, muscular aches and pains, and these may not always be outwardly visible. Diseases often cause a generalised fever (a sign) and most involve some degree of pain or malaise (a symptom). For instance, gastrointestinal diseases may cause vomiting and/or diarrhoea (signs). Throat and respiratory illnesses may cause coughs (signs) and chest pains (symptoms). ### Location The location of a disease may be **local** (confined to a specific area of the body) or **systemic** (a generalised illness that infects most of the body, with pathogens distributed widely in tissues). A rash can be a sign of many types of disease, but its location can often be used to narrow down the possibilities. Figure 2.1 shows a localised rash caused by a fungal infection, while Figure 2.2 shows a systemic rash caused by the chickenpox virus. Start of Figure []{#Session5_Figure1.anchor}Displayed image **Figure 2.1** Localised rash due to a fungal infection within the skin. [View description - Figure 2.1 Localised rash due to a fungal infection within the skin.](#figure-2.1-localised-rash-due-to-a-fungal-infection-within-the-skin.) End of Figure Start of Figure []{#Session5_Figure2.anchor}![Displayed image](media/image18.jpg) **Figure 2.2** Systemic rash caused by chickenpox (varicella zoster) virus. [View description - Figure 2.2 Systemic rash caused by chickenpox (varicella zoster) virus.](#figure-2.2-systemic-rash-caused-by-chickenpox-varicella-zoster-virus.) End of Figure ### Timescale An **acute infection** resolves quickly -- it either kills the host or gets better within days or weeks. When it subsides, this is usually because the pathogen that caused it has been effectively targeted by the host's immune response and its numbers are in decline. A **chronic infection** occurs when the immune system fails to eliminate the infectious agent, which continues to produce disease symptoms and tissue damage over many months or years. For example, the bacterium *Mycobacterium tuberculosis* causes chronic tuberculosis (TB) by infecting host immune cells called macrophages, which effectively hides the bacterium from the immune system. Many parasites, notably the single-celled blood parasites of the genus *Trypanosoma* (the cause of sleeping sickness), evade the immune system by continually making small changes to their outer proteins. This leads to regular relapses or flare-ups in the disease as the new versions proliferate and cause disease symptoms, unchallenged by the immune system. The immune system eventually recognises the latest variant and produces sufficient antibodies to combat it, only for it to be replaced with a new variant. After months of trying to catch up with the ever-changing pathogen, the immune system can become exhausted and begin to fail. A **latent infection** occurs when the infectious agent is not eliminated, but instead persists within the body without producing symptoms. For example, the varicella zoster virus (which causes chickenpox), inserts its DNA into the nucleus of some neurons, where it associates with host proteins, called histones, that tightly associate with portions of DNA to regulate which genes are active at any time. In this state, the virus can persist in the neuron without replicating, and the infection becomes latent. However, years later, and for reasons that are still not fully understood, the viral DNA can become unwrapped from the histone proteins, causing reactivation of virus production and the related viral disease, shingles. 2.3 The diversity of infectious agents --------------------------------------- Infectious agents form one of the most diverse groups you will ever come across. They include members of the viruses, bacteria, fungi, protists and helminths -- the last two may also be referred to collectively as parasites. Note that 'parasites' can also refer to arthropods which attach to the skin such as ticks and lice. Finally, prions are an unusual type of infectious agent -- abnormally folded proteins which accumulate in cells and disrupt their normal functions. Although this module focuses on human health, there's nothing special about humans as far as infectious diseases are concerned -- infections affect all living organisms. For example, the first virus to be discovered (tobacco mosaic virus) is a pathogen of many plants, including: tobacco, tomato, pepper, cucumber, orchid and some species of beans. Start of Figure []{#Session5_Figure3.anchor}Displayed image **Figure 2.3** Orchid leaves infected with tobacco mosaic virus. [View description - Figure 2.3 Orchid leaves infected with tobacco mosaic virus.](#figure-2.3-orchid-leaves-infected-with-tobacco-mosaic-virus.) End of Figure A summary of the characteristics of the main groups of infectious agents is given in Table 2.2 and their relative sizes are shown in Figure 2.4. Each of these groups will be described in further detail in Topic 3. Note that the exact numbers of pathogens are constantly increasing; new strains are either evolving from existing ones or being discovered all the time. The main point to take away from this table is not the fine detail (you don't need to memorise this table), but instead we want you to realise there are a huge variety of infectious agents. Start of Table Table 2.2 Summary of the different types of infectious agent and some of the diseases they cause. **Type of infectious agent** **Number of known pathogens** **Structure** **Common diseases caused** ------------------------------------------------------------- ------------------------------- ------------------------------------------------------------------------------------------------------------------------------------------------------------------ -------------------------------------------------------------------------------------------------------------------------------------------- Viruses \>250 Subcellular particles 10--400 nm diameter COVID-19, hepatitis B, influenza, measles, chickenpox, dengue, Ebola, yellow fever Prions \>5 Infectious proteins \500 Prokaryotes (microscopic single-celled organisms with no nucleus or organelles). 1--2 µm diameter and 2--5 µm long. Individual cells or in short chains of cells Tuberculosis, tetanus, pneumonia, cholera, anthrax, salmonella, legionella Fungi \>300 Eukaryotes (unicellular or multicellular organisms with a distinct nucleus and organelles). Microscopic unicellular yeasts to macroscopic multicellular moulds Candidiasis, pneumocystis, ringworm, Athlete's foot, aspergillosis Protists \>60 Eukaryotes. Microscopic unicellular forms Malaria, trypanosomiasis, leishmaniasis, dysentery Helminths (three categories): flukes, tapeworms, roundworms \>280 Invertebrates. Larval stages a few hundred µm long. Adults range from a few mm to several metres long Schistosomiasis, opisthorchiasis, clonorchiasis, fascioliasis, taeniasis, cysticercosis, ascariasis, guinea worm disease, hookworm disease End of Table Start of Figure []{#Session5_Figure4.anchor}![Displayed image](media/image20.png) **Figure 2.4** Relative sizes of the main types of infectious agents. Note that the length scale is not linear, but changes by 10-fold at each step (i.e. it is logarithmic). For comparison, individual cells in a human body are typically \~100 µm in diameter (10^−4^ m). [View description - Figure 2.4 Relative sizes of the main types of infectious agents. Note that the \...](#figure-2.4-relative-sizes-of-the-main-types-of-infectious-agents.-note-that-the-length-scale-is-not-linear-but-changes-by-10-fold-at-each-step-i.e.-it-is-logarithmic.-for-comparison-individual-cells-in-a-human-body-are-typically-100-%C2%B5m-in-diameter-104-m.) End of Figure From Table 2.2, you can glimpse the astonishing variety that exists among infectious agents, which range in size from small proteins (prions) to intestinal worms several metres long, and include subcellular particles (viruses), prokaryotes (bacteria) and eukaryotes (protists, fungi and helminths). Although each of these agents can cause disease, it is important to realise that just four infectious agents are the largest single contributors to global deaths due to infectious disease, as shown in the pie chart in Figure 2.5. The pie chart shows that in 2019, tuberculosis (caused by the *Mycobacterium tuberculosis* bacteria) caused around 1 208 000 deaths (2.2% of total deaths), AIDS (HIV virus) caused 675 000 deaths (1.2%), malaria (various *Plasmodium* protozoa) caused 411 000 deaths (0.7%), and measles (measles virus) caused 166 000 deaths (0.3%). These have been the top four lethal infections for several years. However, between 2020 and 2022, COVID-19 temporarily became the fifth most lethal infection. Figure 2.5 also includes popout world maps on some of the segments, which we will refer to in the next section. Start of Media Content []{#Session5_MediaContent1.anchor}Interactive content is not available in this format. **Figure 2.5 (interactive)** The major communicable and non-communicable causes of death in 2019. Infectious disease deaths are grouped together as the shaded segment at the top left. Select 'View interactive version' so you can select TB, HIV/AIDS and malaria to reveal death distribution maps per 100 000 people. [View description - Figure 2.5 (interactive) The major communicable and non-communicable causes of death \...](#figure-2.5-interactive-the-major-communicable-and-non-communicable-causes-of-death-in-2019.-infectious-disease-deaths-are-grouped-together-as-the-shaded-segment-at-the-top-left.-select-view-interactive-version-so-you-can-select-tb-hivaids-and-malaria-to-reveal-death-distribution-maps-per-100-000-people.) End of Media Content Many infectious diseases cause similar signs and symptoms. For instance, lower respiratory infections (2 593 000 deaths, 4.7% of deaths) and diarrhoeal diseases (1 519 000 deaths, 2.7%) each cause more deaths than any of the single infectious agents listed above, but they each can be caused by many different types of pathogens. ### 2.3.1 Global distribution of death due to disease The pie chart in Figure 2.5 shows the major causes of death in 2019, both communicable (infectious diseases) and non-communicable. Infectious disease accounts for around 14% (7.7 million) of all deaths that year. The chart is interactive -- you can select TB, HIV/AIDS and malaria to reveal maps that show the global distributions of deaths due to these infections in 2019, as the death rate per 100 000 people. Start of Media Content []{#Session5_MediaContent2.anchor}Interactive content is not available in this format. **Figure 2.5 (interactive, repeat)** The major communicable and non-communicable causes of death in 2019. Infectious disease deaths are grouped together as the shaded segment at the top left. Select 'View interactive version' so you can select TB, HIV/AIDS and malaria to reveal death distribution maps per 100 000 people. [View description - Figure 2.5 (interactive, repeat) The major communicable and non-communicable causes \...](#figure-2.5-interactive-repeat-the-major-communicable-and-non-communicable-causes-of-death-in-2019.-infectious-disease-deaths-are-grouped-together-as-the-shaded-segment-at-the-top-left.-select-view-interactive-version-so-you-can-select-tb-hivaids-and-malaria-to-reveal-death-distribution-maps-per-100-000-people.) End of Media Content Notice that death rates due to TB, HIV/AIDS, and malaria are all highest in sub-Saharan Africa, with TB also showing a high death rate in India. All three of these diseases can be chronic and involve long-term suffering, so it's reasonable to assume the death statistics you have just seen are the tip of the iceberg compared with the number of people currently infected. With this in mind, you should be considering several questions regarding the reported death data: 1. 2. 3. 4. 5. 6. Start of Box Note for factors 5 and 6, these will affect not only the number of cases reported to the health authorities, but could result in delays to treatment that lead to poorer outcomes, including increased deaths. End of Box 1. Start of Activity []{#Session5_Activity2.anchor}**Activity 2.2 Comparing the incidence and deaths due to TB in 2019** You should allow approximately 20 minutes for this activity. Start of Question This activity will help you to achieve [learning outcome 1.2](#learningoutcomes). It also develops the employability skills of problem solving and communication. Figure 2.6 shows maps of the incidence (new cases) of TB per capita (Figure 2.6a) and deaths due to TB per capita (Figure 2.6b) in 2019. Compare the distributions of these two measures. Do they always match, or are there countries where the differences between incidence and deaths seem very large (or very small)? Make some notes on the general trends and any outliers. Start of Figure []{#Session5_Figure5.anchor}Displayed image **Figure 2.6** (a) Incidence of tuberculosis per 100 000 people in 2019. (b) Death rate from tuberculosis per 100 000 people in 2019. [View description - Figure 2.6 (a) Incidence of tuberculosis per 100 000 people in 2019. (b) Death rate \...](#figure-2.6-a-incidence-of-tuberculosis-per-100-000-people-in-2019.-b-death-rate-from-tuberculosis-per-100-000-people-in-2019.) End of Figure The first thing to notice is that TB incidence and deaths per capita generally match. Where incidence is high, death is also high. However, there are a small number of differences. For instance, the incidence in the North African countries of Algeria, Libya, Mali and Niger is very similar. However, there's a huge variation in death rates, with Algeria and Libya having low deaths due to TB, while Mali and Niger had very high death rates due to TB. You should briefly pause here to reflect on the previous list of factors that can affect the reported statistics, and consider some explanations of your own. End of Question [View answer - Activity 2.2 Comparing the incidence and deaths due to TB in 2019](#answer-4) End of Activity As you saw in Activity 2.2, the reasons for discrepancies between TB incidence and TB deaths are multifactorial and likely to be different from country to country. Factors such as surveillance reporting, the efficiency and priorities of different health systems, and any inequalities in access to healthcare can all play a role. ### 2.3.2 TB and HIV tutor group discussion Start of Activity **Activity 2.3 Tutor group forum discussion: TB and HIV** You should allow approximately 1 hour for this activity. You should use 30 minutes for finding information and 30 minutes for the forum discussion. Start of Question This activity will help you to achieve [learning outcomes 1.1, 1.2 and 1.3](#learningoutcomes). It also develops the employability skills of communication, collaboration, and digital and information literacy. The digital and information literacy skills you will develop in this activity will be useful in completing TMA 01. Being able to find, critique and discuss data are essential skills for any scientific workplace. You are going to search for mortality data for TB and HIV by yourself and engage in some guided discussion in the TB and HIV discussions in your tutor group forum. Specifically, you will be addressing two questions about TB and HIV: 1. 2. As a starting point, some suggested websites are [disease factsheets from the WHO](https://www.open.ac.uk/libraryservices/resource/website:152842&f=37143), and [disease factsheets from the CDC](https://www.open.ac.uk/libraryservices/resource/website:152843&f=37143). You should find and quote on the forum information from at least one *primary* source that supports one of the discussion statements above. Primary sources include research papers, conference proceedings and some health service or government reports. (By contrast, secondary sources quote, analyse, and evaluate information taken from primary sources.) Websites such as the WHO are usually secondary sources, but they nearly always provide a link to the primary sources from where they get their information. Consider how reliable and up to date your information sources are, and remember to quote the reference and provide the link to any primary sources you use, as this will help others to locate the same information you found and aid the discussion. Don't worry if you are finding the same information as other members of your tutor group. It is inevitable that you will all discover similar or identical sources. Remember the Library has some useful information about [using PROMPT to evaluate the information that you find online](https://learn1.open.ac.uk/mod/oucontent/view.php?id=15018) and [guidance on referencing different types of material](https://www5.open.ac.uk/library/referencing-and-plagiarism/quick-guide-to-harvard-referencing-cite-them-right?nocache=6605775e0e505). One aim of this exercise is to get you into the habit of verifying the information you find quoted on the Internet or in a paper, by going back to the primary source. As a scientist, this is an essential skill. End of Question End of Activity 2.4 Relationships between infectious agents and their hosts ------------------------------------------------------------ Our bodies are teeming with microorganisms and yet, these very rarely make us ill. Just as with human relationships, the relationships between species can range from being mutually beneficial to completely one-sided and selfish, and the same is true when one species shares a different species' body or resources. The associations listed below demonstrate this range of symbiotic relationships from beneficial to harmful, and show how sometimes a beneficial relationship can break down to become pathogenic. **Symbiosis** (literally meaning 'living together'), is an overarching term describing a close, prolonged relationship between two or more organisms of different species. Many different types of symbiotic relationships can exist, some to a mutual benefit to both organisms but others that can be harmful to one of them. Three symbiotic relationships that are relevant to studying infectious disease are described below -- mutualism, commensalism and parasitism. **Mutualism** describes a relationship where both parties benefit from the situation. It is such a highly interdependent association that one associate cannot survive without the other. A classic example in the animal kingdom is the association between ruminants (a classification of herbivorous mammals, such as cows) and the microorganisms that inhabit their gut (mainly bacteria). Many of these microorganisms have the enzymes necessary to convert cellulose from plant material the ruminant has eaten to glucose, while the ruminant host provides a moist, protective, low-oxygen environment and food that supports the growth of the microorganisms. **Commensalism** is where predominantly only one species, the commensal, benefits from the symbiotic relationship (usually from food and possibly shelter within the other species) while the host remains unaffected. Humans support vast numbers of commensal organisms, mostly bacteria, on their skin and on the mucous membranes of the respiratory, gastrointestinal and genitourinary tracts. For instance, our gut is home to over 2000 different species of bacteria, with over 10^13^ individual bacteria inhabiting a normal adult gut, plus a handful of fungal and protist species. In fact, it's been estimated that there are as many bacterial cells in our gut as there are human cells in our entire body (Sender *et al.*, 2016)! In a healthy body, these commensals do no harm, and some may even engage in mutualism to protect from pathogens by helping to maintain a healthy immune system (EMBL-EBI, 2019; Quigley, 2013). However, sometimes the balance between a host and a commensal shifts, such that the commensal becomes a pathogen. These are called 'opportunistic pathogens'. This can happen when: 1. 2. 3. **Parasitism** is the term given to a relationship between two organisms in which the parasite exploits the host. The parasite benefits from the relationship while the host is harmed in some way. This is the type of relationship we typically consider to be pathogenic. For instance, tapeworms, lice, fleas and some bacteria (e.g. *Chlamydia trachomatis*) have a parasitic relationship with their hosts. Harm caused by parasitism is difficult to define but is usually taken to include competition for nutrients or certain metabolites, destruction of host cells, or alteration of the behaviour of host cells. Figure 2.7 summarises these three forms of symbiotic relationship. Start of Figure []{#Session5_Figure6.anchor}![Displayed image](media/image22.png) **Figure 2.7** A summary of symbiotic relationships. [View description - Figure 2.7 A summary of symbiotic relationships.](#figure-2.7-a-summary-of-symbiotic-relationships.) End of Figure 2.5 Establishing the cause of a disease -- Koch's postulates ------------------------------------------------------------- So far, the term *pathogen* has been used to mean an infectious agent that produces damage or disease. But, as you saw in the previous section, not all microbes are pathogens and conversely, not every infectious agent produces obvious signs or symptoms. How then can an infectious agent be identified as the causative agent of a particular disease? An important start was made in this area by the German physician Robert Koch, who in 1876 identified the bacterium that causes the disease anthrax (*Bacillus anthracis*). Koch took samples from disease lesions on cows that had died of anthrax and viewed them under a microscope, using a dye to stain them. He noticed rod-shaped bacteria in the lesion samples and suspected they might be the cause of the anthrax disease. To help confirm this, he took some of the bacteria from the cow lesions and injected them into healthy mice, which subsequently developed anthrax and demonstrated the same rod-shaped bacteria in their lesion samples. Koch went on to develop techniques to grow pure cultures of suspected disease organisms and did similar transfer experiments with the bacterium that causes tuberculosis. These findings allowed Koch to develop a set of rules to distinguish a pathogenic microbe from a harmless microbe which just happened to be found in the same patient. These rules came to be called **Koch's postulates**, and they state that a microbe is pathogenic if it satisfies each of the following statements: 1. 2. 3. 4. Koch's postulates were very useful in the early days of microbiology. The idea that a disease was caused by a specific microbial infectious agent was a huge advance over the previous ideas that infectious diseases were somehow transmitted by bad odours or spontaneously generated without any causative agent. However, there are some cases where it proved impossible to satisfy all of Koch's postulates, and this was even acknowledged by Koch himself at the time. Start of Activity []{#Session5_Activity4.anchor}**Activity 2.4 Infections that don't obey all of Koch's postulates** You should allow approximately 10 minutes for this activity. Start of Question This activity will help you to achieve [learning outcome 1.2](#learningoutcomes). Using nothing more than your current knowledge of infectious diseases, can you think how it might be possible for an infectious disease to fail to satisfy some of Koch's postulates? Now, see whether you came up with the same ones that we did. End of Question [View answer - Activity 2.4 Infections that don't obey all of Koch's postulates](#answer-5) End of Activity Nevertheless, the basic premise of Koch's postulates -- that a given infectious agent produces a specific disease -- is still of great use and was used in 1977 to prove that Legionnaire's disease is caused by the bacterium *Legionella pneumophila* and, in 2003, that the virus SARS-CoV causes severe acute respiratory syndrome (SARS). The example below describes some of the pieces of evidence that allowed those links to be made between infectious agents and the diseases they cause. Start of Example **Example: Using Koch's postulates to identify pathogens** Legionnaire's disease evidence: The first Legionnaire's disease c

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