Epidemiology Lecture Notes HSS 3110, University of Ottawa - PDF

EPIDEMIOLOGY HSS 3110 Lecture 7 WEEK 7 Emerging infectious diseases What is being done to control NTDs? NTDs Lab 7 Characteristics of NTDs Q&A This pandemic has magnified every existing inequality in our society – like systemic racism, gender inequality, and poverty. -Melinda Gates key concepts Micr...

EPIDEMIOLOGY HSS 3110 Lecture 7 WEEK 7 Emerging infectious diseases What is being done to control NTDs? NTDs Lab 7 Characteristics of NTDs Q&A This pandemic has magnified every existing inequality in our society – like systemic racism, gender inequality, and poverty. -Melinda Gates key concepts Microorganisms that are capable of causing disease are called pathogens/ infectious agents (e.g. bacterium, virus, parasite, or fungus). Many of these microorganisms are harmless, and sometimes beneficial to humans and other organisms e.g. play important roles in environmental and human/animal processes like nutrient cycling and digestion. Opportunistic pathogens are potentially infectious agents that usually do not cause disease in healthy hosts, but can infect immunocompromised or critically ill individuals e.g. HIV+ patients, cancer patients receiving chemotherapy. Pathogenesis is the process by which an infection leads to disease. The same Pathogenesis may cause a mild disease in some hosts and a severe disease in other hosts. An infectious disease is a disease that is caused by the invasion of a host by agents whose activities harm the host's tissues (that is, they cause disease) and can be transmitted to other individuals (that is, they are infectious). The "big three": Malaria, HIV/AIDS, and Tuberculosis. vectors: transmit disease form one host to another (ex. Ticks, spiders) Some may not be alive until they enter host 1. Implantation of virus at the portal of entry: This is the first step in the pathogenic process, where the virus enters the host's body through a portal of entry. For example, respiratory viruses like influenza enter the body through the nose or mouth, while the human immunodeficiency virus (HIV) enters through mucous membranes or breaks in the skin during sexual contact or blood transfusion. 2. Local replication: After entering the body, the virus begins to replicate locally at the site of entry. This replication can cause damage to the host Pathogenic mechanisms cells and trigger an immune response. For example, herpes simplex virus (HSV) can replicate in the skin cells, causing lesions or cold sores. 3. Spread to target organs: The virus can then spread from the initial site of infection to target organs or tissues where it can cause disease. This spread can occur through the bloodstream or lymphatic system. For example, the measles virus initially infects the respiratory tract but can spread to the skin, lymph nodes, and other organs. 4. Spread to sites of shedding: Finally, the virus can spread to sites where it is shed into the environment, allowing for transmission to other hosts. This shedding can occur through respiratory secretions, feces, urine, or other body fluids. For example, the norovirus, which causes gastroenteritis, is shed in the feces and can be transmitted through contaminated food or water. Emerging Infectious Diseases (EIDs) and Re-emerging Infectious Diseases (REIDs) a. Since the 1970s, about 40 infectious diseases have been discovered, including SARS, MERS, Ebola, chikungunya, avian flu, swine flu, Zika and most recently COVID-19. EIDs REIDs some EIDs are NTDs b. EIDs encompass diseases new to humans, those affecting small populations in isolated areas, or those recently recognized as distinct diseases caused by infectious agents. c. REIDs are diseases that were once significant health problems, declined, but are now resurging in importance. d. Specific pathogens, like influenza viruses, exhibit a continuous pattern of emergence and reemergence. These are mostly zoonotic - not from human sources e. Most EIDs and REIDs have a zoonotic origin, emerging from animals and crossing the species barrier to infect humans. f. Zoonoses predominantly come from wildlife, with some originating from domesticated animals and intensive animal farming. g. Factors contributing to EID include population growth, spread in health care facilities, aging population, global travel, and changing vector habitats related to climate change. h. Vector-borne (blood-feeding insects and ticks capable of transmitting pathogens between hosts) diseases are major causes of mortality and morbidity globally. i. Example of EIDs: C auris, Elizabethkingia anopheles, the Lone Star tick, and avian influenza H7N2 Elimination: reduce disease burden to very negligible extent (ex. Malaria) Eradication: completely wiping out the disease form the face of the planet (ex. Polio) Terms used at national levels flu: most talked abt disease in re-emerging diseases because they are resistant to treatment and mutate very easily Vectorborne diseases of concern Disease Pathogen Vector Transmission Malaria Plasmodium falci parum, vivax, ova le, malariae Anopheles spp. M osquitoes Leishmaniasis* Leishmania spp. Lutzomyia & Phle botomus spp. San dflies Zoonotic Trypanosomiasis (NTD) Trypanosoma br ucei gambiense, rh odesiense Glossina spp. (tse tse fly) Zoonotic Chagas disease (NTD) Trypanosoma cr uzi Triatomine spp. Zoonotic From humans to humans through a vector Anthroponotic ex. Degunge and chigunia Hard to get pandemics in control once they are out of control The Challenges for RCTs in Emerging Infectious Diseases Public health surveillance system - makes sure nothing goes undetected report to CDC and get immediate attention for unknown diseases COVID-19 pandemic has forced a rethinking of RCT methodologies, emphasizing adaptability, inclusivity, and efficiency. Contagious diseases like COVID-19 present difficulties for traditional RCTs due to frequent clinic visits, complex assessment schedules, selective participant populations, and centralized academic site concentration. Periodic lockdowns during the pandemic demand flexibility in trial designs to adapt to changing circumstances. Physical distancing and travel restrictions necessitate minimizing unnecessary meetings to reduce risks. Resource-limited settings, especially during outbreaks or in regions with no prior clinical research, face challenges in data collection and quality oversight. Changes in temperature and precipitation can extend the seasonal activity of vectors, allowing them to be active for longer periods and increasing the opportunities for disease transmission. Climate change and vector-borne diseases Climate change —> warmer seasons —> more time for tropical organisms to reproduce —> more exposure displacement of populations, disruption of public health infrastructure, and increased exposure to vectors and vector-borne diseases. Vectors may migrate to new areas as their preferred climate conditions shift Increase animal disease risk & potential human risk Increased animal reservoirs &/or arthropod vectors Low rainfall can create habitat as rivers dry into pools (dry season malaria) Heavy rainfall events can synchronize vector host-seeking & virus transmission How diseases emerge? Genetic variations due to overuse of antibiotics Small proportion of population - don’t get much attention Neglected tropical diseases refer to a group of mainly chronic, debilitating and often stigmatising diseases that primarily affect the poorest of the poor living in remote rural and deprived urban settings of tropical and subtropical countries. NTDs not considered public health issues not financially viable — Pharma companies not concerned w/ them The term "neglected tropical diseases" was coined in 2005 Initially included 13 diseases (7 helminth, 3 bacterial, 3 protozoal). The list expanded to over 40 diseases, including viral, fungal, and ectoparasitic infections. Conflict about what diseases should be called NTDs The majority are poverty-driven bad hygiene + sanitation Results from four classes of causative pathogens: (i) protozoa (Chagas disease, human African trypanosomiasis, and leishmaniasis); (ii) bacteria (Buruli ulcer, leprosy, trachoma, and yaws), (iii) helminths or metazoan worms (cysticercosis/taeniasis, dracunculiasis, echinococcosis, foodborne trematodiases, lymphatic filariasis, onchocerciasis, schistosomiasis, and soiltransmitted helminthiasis); and (iv) viruses (dengue, chikungunya, and rabies). Buruli ulcer(Mycobacterium ulcerans infection) Chagas disease Dengue/severe dengue Dracunculiasis(Guinea-worm disease) Food-borne trematodiases and fascioliasis (liver flukes) Human African trypanosomiasis(sleeping sickness) dont have to occur in tropics to be considered NTD but for some reason, found most commonly in the tropics List of NTDs (WHO) not genetic Human echinococcosis(hydatid disease) Leishmaniasis Leprosy Lymphatic filariasis Onchocerciasis(river blindness) (classified as emerging and re-emerging infectious diseases by US Centers for Disease Control and Prevention) Rabies Schistosomiasis (bilharzia) Soil-transmitted helminthiases Taeniasis/cysticercosis(tapeworms) Trachoma Yaws (endemic treponematoses) Most review articles/ commentaries The infectious agents of NTDs no real treatments to manage or “kill” these diseases viruses (rabies and dengue) bacteria (leprosy, yaws, trachoma and Buruli ulcer) Legs get so sore looks like elephant leg protozoa (leishmaniasis and trypanosomiasis) helminth parasites (schistosomiasis, lymphatic onchocerciasis, intestinal worms and Guinea worm). filariasis, flies, fomites (e.g. skin cells, hair, clothing or bedding) and fingers Transmission Routes of NTDs (trachoma) mosquitoes (dengue fever and filariasis) tsetse flies (sleeping sickness) sandflies (leishmaniasis) blackflies (onchocerciasis) snails, which release infective larvae into water to penetrate human skin (e.g schistosomiasis) Most common the faeco-oral route (e.g. soil-transmitted helminths-see page 29) or via food products. no specific S&S And fever NTDs cause pain and disability, creating lasting health, social and economic consequences for individuals and societies. Characteristics of NTDs The individual diseases are very different, and one person can be affected by more than one disease at the same time. Emerging or re-emerging infectious diseases’ (EReNTDs) present a unique global health challenge. They not only manifest in underserved populations, but are also largely ignored in drug development and may not be included in current disease prevention or control programs Impoverished environments exacerbate disease severity, including poor water sanitation, inadequate housing, rapid urbanization and poor disease vector control, and often lack access to needed healthcare and effective case detection/management. NTDs afflict the poorest people – those without access to the safe water, sanitation, and basic health services required in order to Characteristics of NTDs protect themselves against infection by bacteria, viruses and other pathogens. High-income groups are rarely affected. Mild in most cases Many are chronic, slowly developing conditions that become long latency period progressively worse if undetected and untreated. The damage they cause can be irreversible. They can cause severe pain and life-long disabilities, with long-term consequences for the person and also for family members who have to care for the person. People with NTDs are often stigmatised and excluded from society, and this can affect their mental health. The climatic regions associated with NTDs are typically referred to as Geography of NTDs tropical and subtropical regions. More than 99% of infected people live in 31 African countries. These regions are characterized by warm to hot temperatures throughout the year and high humidity levels. NTDs thrive in these climatic conditions, as they provide favorable environments for disease vectors (such as mosquitoes, flies, and snails) and the parasites or pathogens they transmit. Geography of NTDs Afghanistan lower prevalence in non-africans countries www Why are NTDs called neglected? Reasons for neglect Lack of economic incentives for the pharmaceutical industry Many are asymptomatic and have long incubation periods NTDs are associated with social stigma, making their treatment more complex. Countries having eliminated at least one neglected tropical disease (n=50 as of 1 November 2023) www NTDs and poverty NTDs reflect a country's socio-economic progress. NTD's have a disproportionate impact on these already marginalized communities, compared to developed countries. Long-term disability from disfigurement, pregnancy complications, impaired childhood development and growth, productivity from NTDs fuel an endless ‘poverty trap’. and reduced What is being done to control NTDs? The drugs needed to treat NTDs are now included on the WHO ‘Essential Medicines’ list, and pharmaceutical companies are making them freely available to the populations in need through donation programs. commitment to the control of NTDs and novel approaches to drug distribution Ending the neglect to attain the Sustainable Development Goals: A road map for neglected tropical diseases 2021–2030 (by WHO) What is being done to control NTDs? What is being done to control NTDs? Rare to get research grant for infectious diseases in Canada Class reading www