COMM 801: BASIC EPIDEMIOLOGY PDF

COMM 801: BASIC EPIDEMIOLOGY 6/30/2024 1  STUDY MODULE 1: STUDY SESSION 1 Introduction to Epidemiology 6/30/2024 2 INTRODUCTION TO EPIDEMIOLOGY Definition of Epidemiology You can define Epidemiology as the...

COMM 801: BASIC EPIDEMIOLOGY 6/30/2024 1  STUDY MODULE 1: STUDY SESSION 1 Introduction to Epidemiology 6/30/2024 2 INTRODUCTION TO EPIDEMIOLOGY Definition of Epidemiology You can define Epidemiology as the study of the distribution and determinants of health-related states or events in specified populations and the application of this study to the control of health problems (Last, 1988). Epidemiology was coined from three Greek words: epi, demos, logos, meaning the science of people. Historically, the impact of epidemiology on the health of the nation has been long-standing and far-reaching. Its origins can loosely be traced to the time of Hippocrates (460- 377 BC) who, as a physician, attempted to investigate the occurrence of disease on a rational basis. 6/30/2024 3 INTRODUCTION TO EPIDEMIOLOGY CONT’D. In Britain, its formative roots can be traced back to the works of John Graunt (1662) and William Farr (1839) who laid the scientific basis of the most of epidemiological concepts. We have isolated studies of specific diseases in the early 19th century that gave birth to the epidemiological methods. The studies by John Snow (referred to as the Father of Epidemiology) who, in the 1850s, observed patterns of a cholera outbreak in central London, was a celebrated case scenario. As a result of his analysis of the incidence of cholera and mortality in the affected areas, Snow was able to identify the cause of the cholera epidemic and attributed it to a communal water-pump in Broad Street, Soho. 6/30/2024 4 INTRODUCTION TO EPIDEMIOLOGY CONT’D. Thus, the modern definition of epidemiology accommodates three important elements namely: inclusion of all diseases, populations, and ecological approach. Please you should note the three components (3Ds) common to the definition of epidemiology, distribution, determinants and deterrents of health related events. In addition, the following terms are used to describe the extent of the occurrence of disease: endemic, epidemic and pandemic. The major questions that are usually asked in epidemiology are: who are the group of person(s) affected by the disease, where has the disease occurred and when (time) did it occur? 6/30/2024 5  SIGNIFICANCE OF EPIDEMIOLOGY The following reasons have been adduced for studying these three ‘ds”; disease frequency, distribution and determinants of diseases in human population: 1. For planning and evaluation of healthcare. 2. For identification of the determinants of diseases. 3. For evaluation of method of controlling disease. 4. For observation of the natural history of a disease making up of diagnosis and prognosis. 5. For classification of a disease. 6/30/2024 6  USES OF EPIDEMIOLOGY You should recall from the activity above that the study of disease distribution and causation is central to epidemiology. The broad grouping of the uses occurs is in the following areas namely: 1. Understanding the causation of the disease and the development of hypothesis and their testing. 2. Understanding of geographical or local patterns of the diseases. 3. Administration (i.e.) the planning of health activities and direction of programme to relevant sub-group identified to be at risk. However, epidemiology is used for the following: 1. To analyse the respective role of agent, host and the environment in the development and the natural history of disease. 6/30/2024 7  USES OF EPIDEMIOLOGY CONT’D. 2. To analyse the occurrence and distribution of disease according to characteristics such as age, sex, race, occupation and heredity. 3. To study, outline and define problems of health and disease by the analysis of incidence, prevalence and mortality. 4. To help to complete the clinical features and natural history of diseases by group analysis. 5. To estimate an individual‟s risk of developing a disease and the survival 6. To search for factors related to health and disease through the observation of group custom and habits. 7. For planning and allocation of resources. 8. To evaluate the need for and the effectiveness of health service through field studies. 9. For community diagnosis. 6/30/2024 8  STUDY MODULE 1: STUDY SESSION 2 Types of Epidemiological Studies 6/30/2024 9 TYPES OF EPIDEMIOLOGICAL STUDIES Types of epidemiological studies Epidemiological studies are conducted using two broad designs, namely Observational and Experimental: 1. Observational study design. In this design, you play a “passive” role in the control of the factors investigated. The investigator (you) here is a passive observer; it is also classified into two basic types: descriptive and analytical. A. Descriptive epidemiology includes studies investigating the occurrence and distribution of disease in a defined population. Interesting features of disease or health event are described with the pattern for important subgroups of the population. It generates information which can guide testing hypothesis between health events and associated factors using analytical designs or experimental studies 6/30/2024 10 TYPES OF EPIDEMIOLOGICAL STUDIES CONT’D. I. Cross Sectional Study (prevalence rates) with individuals as unit. II. Longitudinal (incidence rates). B. Analytical Epidemiology, the most popular design testing associations, involves selection of two (or more) study groups which are compared concerning the outcome of interest I. Case-control (Case-reference) with individuals as unit of study. II. Cohort (absolute, relative, attributable risk or follow-up) with individuals as unit of study. 6/30/2024 11 TYPES OF EPIDEMIOLOGICAL STUDIES CONT’D. 2. Experimental/Interventional Studies. The investigator has control over factors being investigated in this design. I. Randomised controlled trials/or Clinical trials with patients as unit of study. II. Field trials or community intervention studies with healthy people as unit of study. III. Community trials with communities as unit of study. 2.1 Observational Studies This is made up descriptive and analytic studies. 1. Descriptive studies This is the study of the occurrence and distribution of a health event within a population by persons, place and time. 6/30/2024 12 TYPES OF EPIDEMIOLOGICAL STUDIES CONT’D. - Time: When is the disease occurring (time distribution)? This includes the year, season, and day of the week, month and the time of the day. Certain diseases are common during the year for example measles in dry season. The procedures in descriptive studies are: · Defining the population to be studied. · Defining the disease understudy. · Describing the disease by: time, place and person. · Measurement of disease. · Comparing with known indices. · Formulation of a hypothesis. The description of diseases is usually done based on some characteristics, which are shown in the table below: 6/30/2024 13 TYPES OF EPIDEMIOLOGICAL STUDIES CONT’D. Table 1: Characteristics frequently examined Time Place Person Condition Year, season Climate zones Age Birth order Month, week Day, Country, urban/rural, local Sex, marital status Family size, height, hour of onset weight Duration Community, towns, cities Occupation, social status, Blood pressure, blood and institutions education cholesterol and personal habits 6/30/2024 14 TYPES OF EPIDEMIOLOGICAL STUDIES CONT’D. 2. Analytical studies This is the second major type of epidemiological studies. While descriptive studies look at the entire population, analytic studies only look at the individuals that are affected within the population. The focus is not to formulate but to test hypothesis. However, even though individuals are evaluated in analytical studies, the inference is made in respect of the population so selected. Analytic studies comprises of two distinct types of designs, these are: Retrospective or case-control study and prospective or cohort study. 6/30/2024 15 TYPES OF EPIDEMIOLOGICAL STUDIES CONT’D. From here, we can determine whether or not statistical association exists between a disease and a suspected factor and if it does, what is the strength of association. In prospective or cohort studies, a group of persons are exposed to causative factors while others are not. A follow-up is made in the nearest future to check the proportion of effects on the exposed and the non- exposed and comparison is then made. 6/30/2024 16 TYPES OF EPIDEMIOLOGICAL STUDIES CONT’D. 2.2 The experimental/interventional studies This is a study in which one group is deliberately subjected to an experience, and is compared with a control group which has not had a similar experience. The use of experiments in this study is done with ethical considerations. It usually involves selection of an individual or communities. The principle of conducting experimental trials is that under the control of the investigator, some system are subjected to manipulation, creating an independent variable whose effect is then determined by the measurement of subsequent events or outcome. This is known as dependent variable. 6/30/2024 17 TYPES OF EPIDEMIOLOGICAL STUDIES CONT’D. 6/30/2024 18  STUDY MODULE 1: STUDY SESSION 3 Basic Measurement in Disease Frequency 6/30/2024 19  BASIC MEASUREMENT IN DISEASE FREQUENCY You must know that there are various basic measurements used in disease frequency, they are referred to as rates. These are incidence and prevalence rates. The mode, median and mean has been extensively discussed previously Definition of rate: In defining a rate, it is important for you to know the number of people (denominator) affected in the entire population (numerator) to be multiplied by 100. Rates help to determine spread. In order to compare populations of different sizes easily, the rate is usually expressed as the number of events in an arbitrary total such as 1000 or 100,000. 6/30/2024 20  BASIC MEASUREMENT IN DISEASE FREQUENCY CONT’D. 2.1 Definition of rate In general, the rate is equal to the number of cases over the number of population in a given unit of time: Number of cases or events in a given population over a period of time 𝑅𝑎𝑡e = ×100 Population in the same area 2.2 Incidence rates (IR) This is the measure of the frequency of new cases of disease in a particular population, the times of onset of which occurred during a specified period of time. Incidence rates are calculated for narrowly defined populations (in terms of age, sex, etc.) during intervals of time as in epidemics are often called attack rates. 6/30/2024 21  BASIC MEASUREMENT IN DISEASE FREQUENCY CONT’D. Attack rates are usually expressed as a percent. A secondary attack rate is a measure of the frequency of new cases of a disease among close contacts of known cases. Secondary attack rates are usually calculated for household contacts. Number of new cases in a given interval of time ۷‫= ܀‬ × Constant Population at risk 2.3 Prevalence rate (PR) Prevalence rate is defined as the proportion of the population affected by a disease at a particular time. It therefore measures the number of people in a population who have the disease at a given time. 6/30/2024 22  BASIC MEASUREMENT IN DISEASE FREQUENCY CONT’D. It measures the existing, both new and old, number of cases of a health event. PR = Number of existingTotal (old + new) cases a given point in time population at risk × Constant You can confirm that there is a clearly evident that a relationship exists between prevalence, incidence and the duration of the disease. Prevalence is important in determining the work load and in planning for facilities, for example, the number of hospital bed required; the relationship changes if the incidence rate is rapidly changing, as in acute epidemic if the average duration of illness changes in response to treatment. Thus, P = I × D Where, P = prevalence, I = incidence, D = duration 6/30/2024 23  BASIC MEASUREMENT IN DISEASE FREQUENCY CONT’D. Other Rates to be Noted Include: Crude rate: This is a rate expressed in terms of the total population. In other words, the denominator of crude rate is the total population of the area being studied, irrespective of the risk of exposure to the event under study. There are three (3) crude rates commonly used. These are: crude birth rate, crude death rate and rate of natural population increase. A. Crude Birth Rate (CBR) this is the number of life births to resident in an area in a calendar year divided by the average population in that population multiplied by 1000. Total number of births in a year CBR = ×1000 Mid−year population 6/30/2024 24  BASIC MEASUREMENT IN DISEASE FREQUENCY CONT’D. B. The Crude Death Rate (CDR) – The total number of death in a year divided by the mid- year population in the area multiplied by1000. Total number of deaths in a year CRD = × 1000 Mid−year population C. Rate of Natural Population Increase (RNPI) – This is the difference between Crude Birth Rate and Crude Death Rate. RNPI = CBR - CDR = RNPI Specific Rates – this is a rate expressed in terms of a sub-group of a population (i.e.) the denominator is not the total population but a selected portion of it based on exposure status. 6/30/2024 25  BASIC MEASUREMENT IN DISEASE FREQUENCY CONT’D. The sub-population may be defined in terms of age or other demographic characteristics like sex, race or as a combination. Examples are those of age, sex and cause specifics, case fatality, and standardised rate. Age Specific Death Rate Number of deaths in the aged (1−5) ASR = × 1000 Total number of aged 1−5 in a year Sex Specific Rate Number of deaths in women age group 15–44 years in a year 𝐌𝐌R= Number of women aged 15−44yrs in the population in a year ×1000 Where, MMR = Maternal Mortality Rate 6/30/2024 26  BASIC MEASUREMENT IN DISEASE FREQUENCY CONT’D. Statistics: You can term this process as collecting, collating, processing, analysing and reporting of data required for planning and operating health services. Data can be collected through primary or secondary source. Your main objective is to provide reliable, relevant, adequate, timely and unambiguous information for health planners who will in turn interpret it for health providers to implement. The health of a community is assessed by data usage which serves as indicators of the health status. The main sets of statistics in epidemiology are: morbidity, mortality and service utilisation statistics. 6/30/2024 27  BASIC MEASUREMENT IN DISEASE FREQUENCY CONT’D. Types of Statistics 1. Descriptive Statistics: This is your branch of statistics that deals with description of characteristic (s) of a finite population. 2. Inferential Statistics: This is another branch of statistics that deals with the science of drawing conclusions on populations based on observations made on representative samples. Sources of data There are three (3) main sources of data for statistics. These are: census, vital and health statistics. 1. Census is a periodic head count that provides data for planning and determination of legislative representation at the national level. 6/30/2024 28  BASIC MEASUREMENT IN DISEASE FREQUENCY CONT’D. 2. Vital statistics are statistics that records vital events such as births, death, marriages, annulment and divorce obtained at registration centres at local, state and at federal levels. The data are used to generate information for whole groups or entire population. 3. Health Statistics are a combination of vital statistics and other data pertinent to health. In the operation of health services, data can be derived from resources and institutional records. This can be further explained as being derived from: o Notification of diseases which is routinely done. Diseases may be infectious or non- infectious. o Institutions which includes hospitals, health centres, dispensaries and private hospitals 6/30/2024 29  BASIC MEASUREMENT IN DISEASE FREQUENCY CONT’D. o Special programme like school health services, maternal and child health, disease control programme such as Tuberculosis, Leprosy. o Epidemiological survey which includes the whole population or sample in case of an epidemic. Morbidity and mortality statistics as well as health services needs and utilisation data can be derived from health Statistics. Morbidity statistics includes data on occurrence and determinants of diseases in a community obtained from medical health service points. While mortality statistics measures the frequency and determinants of deaths including severity of diseases and other health events. 6/30/2024 30  BASIC MEASUREMENT IN DISEASE FREQUENCY CONT’D. Statistics from other sectors As you may know there are other sectors apart from health where data can be collected to assist in planning for health care of the people. These include: education, public works such as housing, water supply and sanitation, agriculture in regards to food production and distribution as well as economic planning and development which provides the poverty and economic indicator. Uses of Statistics Statistics is used for the following, among others: 1. To measure the health status of the people and quantify their health problems. 6/30/2024 31  BASIC MEASUREMENT IN DISEASE FREQUENCY CONT’D. 2. For health comparison at local, national and international levels. 3. For planning, administration and effective management of health services and programme. 4. For assessment of health services in relation to the set goals. 5. For assessing of the attitudes and degree of consumers satisfaction to healthcare. 6. For health research 6/30/2024 32  BASIC MEASUREMENT IN DISEASE FREQUENCY CONT’D. Data collection There is a basic source of data, which is of primary importance in epidemiology. It is called CENSUS: it provides the denominator for the calculation of rate. Census is a periodic count or enumeration of a population that is usually done every ten (10) years. Census is massive undertaking to contact every member of the population in a given time and collect a variety of information; which is used to derive population pyramid. A population pyramid is the age and sex structure of the population displayed in the form of histogram showing the percentage distribution of each sex at 5 yearly intervals. 6/30/2024 33  BASIC MEASUREMENT IN DISEASE FREQUENCY CONT’D. The primary function of census is to provide information such as total count of population and breakdown into groups and subgroups such as age and sex distribution. The data to be collected will include age, sex, colour, marital status, relationships to head of households, occupation, housing, address, name, educational level, parity, employment status, and income. Methods and sources of data collection We shall now consider various methods of data collection. These include: 1. Use of questionnaire in households. 2. Physical examination. 3. Special investigation. 6/30/2024 34  BASIC MEASUREMENT IN DISEASE FREQUENCY CONT’D. 4. Sample registration forms a population or group. 5. Sources related to utilisation services. 6. Data collected from routine medical examination. 7. Census. 8. Registration of vital events. 9. Notification of disease. 10. Hospital records. 11. Data from environment. 12. Population surveys. 13. Epidemiological surveillance. 6/30/2024 35  STUDY MODULE 1: STUDY SESSION 4 Strategies of Epidemiology 6/30/2024 36  CHAIN OF EPIDEMIOLOGY The following chain exist in the study of epidemiology, they are: 1. Descriptive studies: In which there is data aggregation and analysis, this allows for generation of hypothesis which stipulates possibility of possible association between two or more variables. 2. Analytical study: The hypothesis generated in phase I is tested statistical significance in the relationship between the exposure and outcome variables. Result obtained here may suggest further studies or new hypothesis is formulated. 3. Where there is need to alter the pattern of the relationship between the variables or introduce other factors to attain the desirable outcome, this is carried out through experimental or interventional study design. 6/30/2024 37  CHAIN OF EPIDEMIOLOGY CONT’D. Chain of Epidemiology (Refer to Fig. 1.4.1) (1) Descriptive (2) Hypothesis, generation (3) Analytical studies (Testing hypothesis) (4) Experimental Studies 6/30/2024 38  DISEASE CAUSATION Disease causation In disease causation, ecological factors are important. Ecology is the study of relationship of organisms including humans to each other as well as other aspects of the environment. This has given rise to the concept of the multiple causation of disease that is multi-factorial ethology of disease. There are other factors necessary for the development of disease, namely: a. Level of immunity. b. The environmental conditions. c. The agent factors which must be present for the particular disease to occur 6/30/2024 39  FACTORS THAT INFLUENCE DEVELOPMENT OF THE DISEASE There are factors that precipitate the cause of diseases, these are the host factor (HF) and the environmental factor (EF). 1 Host factor: these are intrinsic factors, genetic (inborn) in a person. It can also be:  Specific (i.e.) not inborn but acquired by immunisation and natural infection.  Personality – people working hard, ambitious with strong drive.  Social class membership – peer grouping, organisation. 2 Environmental factors: these are sub-divided into three namely: biological, physical and social factors. a. Biological factors: These cause diseases that easily pass from one person to another through direct (person-to-person) transmission or indirect (vehicle, fomites, vectors) transmission. 6/30/2024 40  FACTORS THAT INFLUENCE DEVELOPMENT OF THE DISEASE CONT’D. b. Physical factors: It includes heat, light, air, water, radiation, chemical agent, atmospheric pressure. c. Social factor: This is defined as the overall economic and political organization of a society and the institutions by which individual are integrated into the society at various ages of their lives. Social environment is man-made environment which includes what he has created to make life worth living e.g. housing. It also includes the people’s customs, levels of integration of the community, levels and systems of Medicare, the degree of enforcement of health law and code. 6/30/2024 41  FACTORS THAT INFLUENCE DEVELOPMENT OF THE DISEASE CONT’D. Our state of health depends on a balance of forces in a dynamic equilibrium. If the equilibrium is precarious, then the disease occurs easily. If the equilibrium is stable then the disease does not occur very easily. See this ecological model showing the state of equilibrium in disease state. 6/30/2024 42  INTERRELATED FACTORS CONT’D. Ecological model (Epidemic triad) Host Agent Environment Fig. 1.4.2: Epidemic Triad 6/30/2024 43  INTERRELATED FACTORS CONT’D. B. Web of causation The year 1960 marks the first mention of the 'web of causation' in the epidemiologic literature. Not coincidentally, it appeared in the first formal epidemiologic textbook ever published in the United States, Epidemiologic Methods, by Brian MacMahon, Thomas F. Pugh, and Johannes Ipsen Diseases do not just happen but effects depend on single isolated cases which develop as a result of chain of position in which each link is the result of a complex genealogy of antecedence. If the link in the chain is broken anywhere, the disease may not occur (Refer to Fig. 1.4.3: Webs). 6/30/2024 44  INTERRELATED FACTORS CONT’D. Fig. 1.4.3: Web Causation of Disease 6/30/2024 45  INTERRELATED FACTORS CONT’D. C. The wheel model Wheel model tends to emphasise that the contributions of the different components are not equal in any specific disease. It is worthy of note that the host has the genetic core and this determines prognosis/severity. You may not know the agent of a disease before its modification. Killing of mosquitoes may reduce the malaria episodes. Counseling is used in Sickle Cell Disease (SCD) to reduce genetic core. This is a way of manipulation. Manipulation sometimes leads to another problem e.g. use of insecticide in killing mosquito. An impact assessment is therefore necessary in carrying out a manipulation. 6/30/2024 46  INTERRELATED FACTORS CONT’D. Physical Host Social Biology 6/30/2024 47  LEVELS OF PREVENTION Control is assumed as the ultimate aim of epidemiology but now prevention seems taking the lead. In a narrow common usage prevention means the inhibition of the development of a disease before it occurs but in the broader sense. Prevention also includes all measures, which interrupt or slow the progression of disease and the resulting disability. Prevention in epidemiology is divided into four main stages. - Stage1: Primary prevention Primary prevention has two components: general health promotion (GHP) and specific measure (SM). +2GHP includes health education, environmental sanitation and good housing, while SM includes chemoprophylaxis, immunization and good nutrition. 6/30/2024 48  LEVELS OF PREVENTION CONT’D. This is the prevention stage that reduces exposure of an individual or you alter the susceptibility of either being affected by the disease or not. - Stage 2: Secondary prevention The second stage is the stage of early diagnosis and treatment. Any measure that will interfere with the progression of the disease. The measures that constitute early detection are: screening, case finding, mass X-ray to determine lung diseases and smear to detect cancer of cervix in a woman. - Stage 3: Tertiary prevention The third stage of prevention is rehabilitation. This is the alleviation of disabilities from the disease and attempt to restore effective functioning. Rehabilitation can be divided into three (3) forms; 6/30/2024 49  LEVELS OF PREVENTION CONT’D. a. Medical rehabilitation: This is the process of medical care aimed at developing functional and psychological liabilities of the individual. Compensatory mechanism is put in place so as to enable the victim to attain self-dependence and live a full life. b. Social rehabilitation: A part of rehabilitation that aims at the integration of a disabled person into society by helping him to adjust to the demand of the family, community and occupation while reducing any economic and social burden that may impede the social rehabilitation process. It is important in diseases with stigma such as leprosy, pulmonary tuberculosis and mental illness. 6/30/2024 50  LEVELS OF PREVENTION CONT’D. Counseling, social evaluation, individual and community counseling, provision of services including psychiatric services, recreation facilities are components of social rehabilitation. c. Vocational rehabilitation: This includes provision of those vocational services, vocational guidance, training, selective placements which are designed to enable a disabled person to retain a suitable employment. He may require counseling, vocational training, vocational evaluation, proper placement or being looked after by others. 6/30/2024 51  SURVEILLANCE Surveillance is the exercise of continuous scrutiny of and watchfulness over the distribution and spread of infection and the related factors with sufficient accuracy and completeness to provide the basis for effective control. This idea has three main features namely: 1. Systematic collection of all related data. 2. Orderly collation and evaluation of each data. 3. Prompt dissemination of results for action to relevant authority. The following are examples of sources of epidemiological data in the surveillance of disease: Registration of deaths, notification of disease and reporting of epidemics, laboratory investigations, data from routine screening e.g. blood donors, investigation of individual cases and epidemics, epidemiological surveys, data from clinics, distribution of the animal reservoir and the vector production and distribution and care of vaccines, serum and drugs, demographic and environmental data and non-medical statistics. 52 6/30/2024  SURVEILLANCE CONT’D. Objectives of surveillance There are two main objectives in surveillance. These are: 1. The recognition of acute problems so that immediate action is taken. For instance, the recognition of an outbreak of cholera in any area so as to “curb”/limit its spread to that affected area only. 2. To provide broad assessment of specific problems in order to discern long-term trends and epidemiological patterns. This is useful as basis for planning, implementation and assessment for programme of control and prioritisation of public health programme. 6/30/2024 53  STUDY MODULE 2: STUDY SESSION 1 Epidemics 6/30/2024 54  EPIDEMICS Definition and Terms Used in Epidemics We define epidemics as the occurrence in a community or region or a member of a defined population of a group of illnesses of a similar nature in excess of a normal expectancy in that population. In epidemics, any kind of disease or injury may be involved and there are no universally applicable number of cases and no clear geographical extent e.g. food poisoning. However, it can affect a large population. A disease can be said to be endemic in contrast to epidemics. This is a constant presence of a disease or an infective agent within a given geographical area; it is the usual prevalence of a given disease within an area. 6/30/2024 55  DEFINITION OF EPIDEMICS CONT’D. Endemic: This is the constant presence or the usual prevalence of a disease or infectious agent in human populations within a given geographic area. Hyper-endemic: is a term that expresses a persistent intense transmission of the disease e.g. malaria Epizootic and enzootic: are expressions that are equivalent of epidemic and endemic as it applies to animals e.g. epizootic of yellow fever in Monkey which precedes that of yellow fever in man. It is the incidence of disease in animal. Herd immunity: This is the resistance of a group to the introduction and spread of an infectious agent. 6/30/2024 56 DEFINITION OF EPIDEMICS CONT’D. Such resistance is based on the immunity of a high proportion of individual members of the group and on the uniform distribution of the immunes within the group. Propagated-source epidemic: An epidemic in which infections are transmitted from person to person or animal to animal in such a fashion that cases identified cannot be attributed to agents transmitted from a single source. Epidemiologist: An epidemiologist is a public health professional who applies epidemiologic principles and methods to the prevention and control of disease. 6/30/2024 57  PROPAGATION OF EPIDEMICS Epidemics only affect a susceptible number of populations. There is an incubation period before manifestation of symptoms; however, susceptible persons may develop in-apparent infection. The infectious agent may leave the host during the communicable period which varies in timing, and duration with each disease. The following are the sequence of events:  Introduction of the agent  Attack unsusceptible  Acquisition of immunity  Reduction in the number of susceptible  Decline of the epidemic However it is worth noting that the cycle described above can be influenced by any of these factors namely: immunity decline, migration and birth/death. 6/30/2024 58  TYPES OF SPREAD We have two major types of spread in any epidemic; these are common vehicle epidemic and latent case. We shall consider each of the spread turn by turn. i) The Common Vehicle Epidemic This is also called the point source. Transmission here may be through water, food, air or by inoculation. When the epidemic results from a single exposure of the population it is called a point source epidemic. Sometimes there may be repeated multiple exposure or a continued exposure over a period of time e.g. a contaminated well (point source). It is a point source at the closing up and if from the closing up there is continuous drinking from the source (contaminated well), then it becomes a multiple source. 6/30/2024 59  TYPES OF SPREAD CONT’D. a) Characteristics of Common Vehicle Epidemics  Explosive in onset  Limited in time, place and person (i.e.) there is geographical limitation  Serial transfer or propagation: this usually involves a transfer from host to host.  The spread can be by contact, direct or indirect between the infected and susceptible.  Route is respiratory, oral-faecal or genital. b) The index case This is the first among a number of similar cases which are epidemiologically related. Index cases are often identified as a source of contamination or infection. 6/30/2024 60  TYPES OF SPREAD CONT’D. Typically, a common vehicle epidemic shows a rapid rise and a fall within one incubation period whereas in propagated epidemic new cases continue to develop beyond one incubation period. You should note the following: That a typical point source epidemic may be affected by the development of secondary source, for example, water that is infected gives diarrhoea. By the continuous contamination of the source, it ceases to give the picture of point source but multiple sources. A disease that has a long incubation period will give the type of a long epidemic curve with serial transfer. 6/30/2024 61  TYPES OF SPREAD CONT’D. On the other hand, a propagated epidemic may look highly infectious with short incubation period. Geographical mapping can be done to determine the geographical location of the victims and a spread can occur from centre to sub-boundary regions. The geographical marking and epidemic curve can help determine the type of epidemic and the source. 6/30/2024 62  INVESTIGATION OF EPIDEMIC You have being exposed to some details of epidemics, it must be stated clearly that some defined steps are spelt out for investigating epidemics you must follow these steps systematically. They include the following: 1. Verification of the diagnosis: Your diagnosis must include what type of disease is been viewed using full history of presenting signs and symptoms. The first most important step is developing step wise case definition which includes; suspected case, probable case and confirmed case. 2. Confirmation of the existence of an epidemic. This is done by:  Where there is a robust surveillance, an increase in number of cases in from the baseline is easily ascertained, whence an outbreak could be confirmed. 6/30/2024 63  INVESTIGATION OF EPIDEMIC CONT’D.  In the absence of surveillance data, practical alternatives include looking at the previous clinical records and data, questioning the local people in order to obtain approximate estimate of the previous incidence of the disease in the area.  Do a mapping. An epidemic curve to see the number rising, a map to show that cases are spreading. 3. The identification of the affected persons and their characteristics: You should identify who is affected, in terms of age, sex, name, occupation, etc. You should obtain their recent movement, time of onset of their symptoms, find out whether they were previously immunised, and find out their contacts within the incubation period of the disease so that you will be able to follow the contact. Also, you should endeavour to look for additional cases that may be concealed and not typical in nature. 6/30/2024 64 INVESTIGATION OF EPIDEMIC CONT’D. Identify a common experience shared by all of those affected e.g. do they all go to the same venue when they ate the food (ceremonies)? Was the water contaminated from source or a sick person visited the family of recent? All of these provides for epidemiological description of those affected. 4. Study the environmental conditions at the time of the outbreak and compare with the previous condition. Find out if there is any change in water source, weather, food, housing conditions, population of human beings and any environmental change for epidemic invasion. 6/30/2024 65  INVESTIGATION OF EPIDEMIC CONT’D. 5. You should formulate a hypothesis. Drawing from line listing and characterisation of affected persons and population at risk at step 4, an analysis of the available data will help in identifying a possible link between particular exposures with the disease/health event under investigation. Applying basic inferential statistics, usual case control study model, the strength of association between exposure and outcome will be established, which provides a strong pointer to causal relationship. Management of the cases affected. 6/30/2024 66 INVESTIGATION OF EPIDEMIC CONT’D. Following strong epidemiologic evidence of relationship between suspected exposures with the disease outbreak, empirical control measures will be instituted while the other steps of outbreak investigation are carried out. These include:  Treatment of cases by health personnel  Isolation of infected individuals, and imposition of quarantine so as to reduce movement from one point to the other as well as education of the community to obtain cooperation.  Immunisation of susceptible hosts, for certain outbreaks of communicable diseases  Measures are taken to prevent spread and control of epidemics such as hyper chlorination of wells in cholera outbreak and treatment of close contacts with rifampicin in meningitis outbreak. 6/30/2024 67 INVESTIGATION OF EPIDEMIC CONT’D.  Rehabilitation facilities. Permanent control measures are also put in place which includes any of the following: personal hygiene, health education, water supply, vector control, food hygiene legislation, continuous vaccination programme. Rehabilitation facilities and strengthening of public health institutions is one of the steps taken in outbreak management. 6. Conduct further laboratory and immunological investigation of the population to confirm the causative agent and isolate its strains. Carriers are deduced e.g. cholera, cerebro-spinal meningitis to identify the type of organism and therapy sensitivity. 7. Report writing. This is usually written in various formats for different target audience which general population, health planners and a scientific community. 6/30/2024 68 STUDY MODULE 2: STUDY SESSION 2 Epidemiology of Communicable Diseases 6/30/2024 69  EPIDEMIOLOGY OF COMMUNICABLE DISEASES Definition A communicable disease is an illness that occurs due to a specific causative agent or its toxic products (e.g. toxins) which arises through transmission of that agent or its products from a reservoir to a susceptible hosts either directly as from an infected person or animal or indirectly through an intermediate plant or animal host, vector or the inanimate environment. 6/30/2024 70  EPIDEMIOLOGY OF COMMUNICABLE DISEASES 6/30/2024 71 EPIDEMIOLOGY OF COMMUNICABLE DISEASES CONT’D. Infectious agent Infectious agent is any organism or agent that is capable of producing infection or infectious diseases. Infection is the successful invasion of the body by microorganisms. You have discussed this extensively in applied sciences for nurses. You should note that infection is not the same as infectious disease and contamination because infection can be apparent or manifest. 6/30/2024 72 EPIDEMIOLOGY OF COMMUNICABLE DISEASES CONT’D. A reservoir is any human being/animal/arthropod/plants/soil or inanimate matter in which an infectious agent normally lives and multiply and on which it depends primarily for survival and reproduces itself in such manner that it can be transmitted to a successive host. Man is the only reservoir of infection of many diseases: (man to man). Occasionally an animal may serve as the reservoir and this is called zoonosis. A zoonosis is an infectious disease transmissible under natural conditions from vertebrae animal to man, for instance, rabies, trypanosomiasis, yellow fever (jungle type), anthrax, Lassa fever from rat and tape worm. 6/30/2024 73 CONCEPTS IN COMMUNICABLE DISEASE Incubation Period: We call this as the period between the exposure to an infectious agent and the appearance of the first signs and symptoms of disease (Refer to your Fig. 2.2.1). It is worthy for you to note here that the (d) point is the variable. Here the patient can go into convalescence, chronic illness or death can occur. Characteristics influencing diseases/illness formation There are characteristics that influence disease/illness formation in the body. These are: Infectivity, Pathogenicity, Virulence, Antigenic power, 6/30/2024 74  CONCEPTS IN COMMUNICABLE DISEASE CONT’D. Resistance This is the ability of infectious organisms to adapt to the antimicrobial drugs designed to kill them, making the drugs ineffective. People infected with antimicrobial-resistant organisms are more likely to have longer, more expensive hospital stays, and may be more likely to die as a result of an infection. Carrier We say a carrier is someone who though has disease causing organism in his body but do not show any sign of infection. The carrier has the ability to harbour and disseminate the parasite without showing any clinical evidence of infection. 6/30/2024 75  CONCEPTS IN COMMUNICABLE DISEASE CONT’D. There are times when even carriers of a disease are more than those showing the signs of the disease. They often become chronic carriers but this does not last long. Some of the disease known to have carriers include: Cholera, Salmonella typhi, Poliomyelitis and Diphtheria. Types of Carrier 1. Incubatory carrier is one that is transferred during incubation period. 2. Convalescent carrier is one that is transferred during recovery period. 3. Intermittent carrier is one that is on and off. 4. Chronic carrier is one in which the individual keeps carrying the disease on for a long time. 6/30/2024 76  CONCEPTS IN COMMUNICABLE DISEASE CONT’D. 5. Healthy carrier is someone who does not show the manifestation of the disease at any time but keeps on transmitting it to people. i) Immunity This is the resistance usually associated with possession of antibodies having specific actions on the micro-organism concerned with a particular infectious disease or its toxin. An individual is considered immune when he possesses specific protective antibodies or cellular immunity as a result of previous infection or immunisation or by previous experience. Immunity can be natural or acquired. Natural is inherent in the individual or species and it is independent of previous infection. Acquired also can be active and passive. Active acquired immunity can be natural or induced, while passive acquired may be natural/trans-placental or passive induced. 6/30/2024 77  CONCEPTS IN COMMUNICABLE DISEASE ii) Active immunity CONT’D. This is the immunity an individual develops as a result of infection or specific immunisation and usually associated with antibodies or cells having a specific action on the disease or toxin. This can be acquired through any of the following: After infection e.g. measles After an apparent infection e.g. Poliomyelitis After immunisation with an antigen which may be killed vaccine. iii) Passive immunity This is the transfer of antibodies produced in one body to another to induce protection against disease. This is useful for individual who cannot form antibodies or for the normal host who takes time to develop antibodies after active immunisation. 6/30/2024 78  CONCEPTS IN COMMUNICABLE DISEASE CONT’D. Here the body depends solely on ready-made antibodies. This can be derived from any of the following:  When an antibody is administered  Transfer of maternal antibodies across the placenta  Transfer of lymphocytes to induce passive cellular immunity. iv) Herd immunity This is the level of resistance of a community or group of people to a particular disease; it provides an immunological barrier to the spread of disease in the human herd. v) Vaccine This is an immuno-biological substance designed to produce specific protection against a given disease. It stimulates the production of protective antibodies and other immune mechanisms. It may be prepared from live modified mechanism or 6/30/2024 79 inactivated or killed organisms. CONTROL OF COMMUNICABLE DISEASE Table 2.2.2: The General Methods For The Control Of Communicable Disease Preventive Control of Epidemic International Measures Patients and Measures Measures Environment (a) Vaccination (a) Measures Measures to limit (a) Control of against epidemic designed to spread of international prevent spread of Communicable travelers, infection matters to disease which has immigrant, animal person and to the developed widely products and the environment in a group or means of transport community within of the above an area, state or nation: b. Chlorination of (b) Keeping (a) of occurrence (b) Inter- water supplies contact under the appropriate government surveillance during health arrangement, incubation periods national laws c. Pasteurisation of (c) Keeping (b) Mass (c) Monitoring milk records under immunization immunization control until found posts especially the to be of infectious boarders and ports. agents d. Control of (d) Reporting local (c) Health rodent authority education 6/30/2024 80  CONTROL OF COMMUNICABLE DISEASE Table 2.2.2: The General Methods For The Control Of Communicable Disease Continued Preventive Control of Epidemic International Measures Patients and Measures Measures Environment e. Control of (e) Isolation (d) Source and Animal contact investigation f. Public health (f) Concurrent education disinfection g. Improvement of (g) Quarantine i.e. sanitation and limitation personal improvement person exposed to infection h. Chemoprophyla (h) Immunisation e.g. malaria, of specific contact filariasis, meningococcal, meningitis, Bacillary, dysentery. (i) Specific treatment 6/30/2024 81 STUDY MODULE 2: STUDY SESSION 3: Epidemiology of Non- Communicable Diseases 6/30/2024 82  OVERVIEW OF THE NON-COMMUNICABLE DISEASES Non-communicable diseases (NCDs) are not passed from person to person but are driven by forces that include ageing, rapid unplanned urbanization, and the globalization of unhealthy lifestyles which may be acute or chronic. Our discussion here will cover the chronic diseases. This will include all ailments or deviation from normal which have one or the following characteristics: – Permanent disability – Leaves residual disability – Caused by non-reversible pathological change – It requires the special training of the patient for rehabilitation – t may be expected to require a long period of supervision, observation and care. 6/30/2024 83  OVERVIEW OF THE NON- COMMUNICABLE DISEASES CONT’D. You will agree with me that, with the control of communicable disease in some part of the world, a change occurs in the demographic picture leading to an older population. This is why chronic disease has become the commonest cause of morbidity and mortality. Non-communicable diseases include cardiovascular, renal, nervous and mental diseases, musculo-skeletal conditions such as arthritis and allied diseases, chronic non-specific respiratory diseases (e.g. chronic bronchitis, emphysema, and asthma), permanent results of accidents, senility, blindness, cancer, diabetes, and obesity and various other metabolic and degenerative diseases and chronic results of communicable diseases. Disorders of unknown cause and progressive cause and often labeled “degenerative”. 6/30/2024 84  THE RISK FACTORS OF NON- COMMUNICABLE DISEASES There are six (6) major key sets of risk factors that are responsible for major distribution of non-communicable disease in relation to its morbidity and premature mortality. These are: 1. Use of cigarette and other forms of smoking. 2. Alcohol abuse. 3. Failure or inability to obtain preventive health services e.g. hypertension control, cancer detection and management of diabetes. 4. Life-style changes e.g. dietary patterns, physical activity. 5. Environmental risk factors e.g. occupational hazards, air and water pollution and possession of destructive weapons. 6. Stress factors. 6/30/2024 85  PROBLEMS OF INVESTIGATING NON-COMMUNICABLE DISEASE We have some problems in the understanding of the natural history of chronic/non- communicable disease investigation which invariably results in difficulties in causal investigation and research. 1. Absence of a known agent: the absence of a known agent makes both diagnosis and prevention difficult, e.g. cancer. 2. The multi-factorial nature of the aetiology (cause) because most chronic diseases are caused by multiple factors. There is rarely a simple one-to-one cause effect relationship and in the absence of a known agent, the term “risk factor/s is used to describe certain factors in relation to a person’s background or lifestyle. Occasionally it can result from cumulative effects of multiple factors and may be addictive or synergistic. 6/30/2024 86  PROBLEMS OF INVESTIGATING NON- COMMUNICABLE DISEASE CONT’D. 3. Long latent period (incubation period) between the first exposure to suspected cause and the eventual development of disease which is often difficult to determine. It is assumed that what is happening now to someone may result from the effect of past happenings. 4. Indefinite onset so that the incidence rate is difficult to calculate. Most chronic disease is slow in onset and development and the distinction between diseased and non-diseased states may be difficult to establish. An example of this is cancer which by the time the patient seeks medical attention, the damage would have been irreversible or difficult to treat. 5. The differential effect of the factors on the incidence and the cause of the disease. 6/30/2024 87  STUDY MODULE 2: STUDY SESSION 4: Sexually Transmissible Infections 6/30/2024 88  SEXUALLY TRANSMISSIBLE INFECTIONS Communicable diseases are sometimes classified by way of transmission. The same applies in case of sexually transmissible infections. Even when sexually transmissible infections are predominantly transmitted through sex, you should note that there are situations where sex is not directly involved, for instance, the unborn baby can contract gonorrhoea from the womb. The issue of HIV is another example. Aside from sex, you must have learnt that HIV can be transmitted through other means like the exchange of blood and other bodily fluids (through the sharing of infected body- piercing instruments); transfusion with infected blood and blood products and also from mother to child. This can occur during pregnancy, during birth or through breast- feeding if the mother is infected with HIV. 6/30/2024 89  WHAT ARE SEXUALLY TRANSMISSIBLE INFECTIONS? You should note that sexually transmissible Infections are bacterial, viral, and parasitic infections, transmissible through sexual contacts. They usually affect the genital areas. They may also cause serious disease complications to the body. Sexually transmissible infections were, over the years, known by some other names; they used to be called venereal diseases (VD). This name was purportedly derived from the Roman goddess of love, and later, the name changed to sexually transmissible diseases (STDs). 6/30/2024 90  WHAT ARE SEXUALLY TRANSMISSIBLE INFECTIONS? In recent times, the name sexually transmissible infections are used. This is because it has been found that not all infections will get to the stage of disease, e.g. HIV infection. The fact that someone is infected with HIV does not mean he would eventually contract AIDS. But that is if he/she manages the condition very well through adequate diets, rest and medication. There are many organisms transmitted through sex and that can lead to diseases. 6/30/2024 91  TYPES OF SEXUALLY TRANSMISSIBLE INFECTIONS 1. Gonorrhoea This is caused by a bacterium called Neisseria gonorrhoea. It is transmitted through intercourse and by oral-genital and anal- genital contact. There is need for warmth and moisture provided by the mucus membranes of the vagina, mouth, or anus for the Neisseria gonorrhoea to survive. Because of this, it is not too likely for you to contract gonorrhoea by sharing someone else’s towel or from sitting on a public toilet seat, unless the bacterium had just been deposited there. Even then, the place should be warm and moist for the pathogen to survive. 6/30/2024 92  TYPES OF SEXUALLY TRANSMISSIBLE INFECTIONS 6/30/2024 93  TYPES OF SEXUALLY TRANSMISSIBLE INFECTIONS CONT’D. 2. Syphilis The organism that causes syphilis is called Treponema pallidum. It is a corkscrew-like organism, which resembles bacteria. Like the gonorrhea bacterium, the organism causing syphilis can survive only in the warmth and moisture by the mucous membranes of the human body. The organism dies quickly outside the body. For this reason, you can hardly contract syphilis from a toilet seat. Syphilis can be detected through a simple blood test. 6/30/2024 94  TYPES OF SEXUALLY TRANSMISSIBLE INFECTIONS CONT’D. 3. Genital Herpes You should note that there are two types of herpes simplex viruses. Type 1 results in cold sores in the mouth, while Type 2 causes genital herpes. In about two to 10 days after the virus has entered the body, some symptoms begin to appear. The symptoms include sores and swollen glands (around the groin). At this stage, you will start to experience flu-like symptoms (fever, muscle aches and a sick feeling). Also, pain in the genital area during urination or intercourse may occur. There may also be fatigue, swelling of the legs and watery eyes. 6/30/2024 The treatment of syphilis is handled medically. 95  TYPES OF SEXUALLY TRANSMISSIBLE INFECTIONS CONT’D. 6/30/2024 96  STUDY MODULE 3: STUDY SESSION 1: Consequences of Sexually Transmissible Infections 6/30/2024 97  CONSEQUENCES OF SEXUALLY TRANSMISSIBLE INFECTIONS Introduction Sexually transmitted diseases are responsible for an enormous burden of morbidity and mortality in many developing countries because of their effects on reproductive and child health, the consequences can be very serious. This is why STIs should be properly treated. You should note that in women, pelvic inflammatory disease (PID) can come with the following associated complications: e.g. infertility, ectopic pregnancy leading to maternal mortality; chronic pelvic pain, and increased possibility of subsequent pelvic infections. 6/30/2024 98  SEXUALLY TRANSMISSIBLE INFECTIONS AND CONSEQUENCES Case Study: Awaiting result Miss X, a young school leaver, contracted gonorrhoea while awaiting her school certificate examination result. Instead of going to the hospital, she discussed the problem with her friends, who gave her some drugs to use. Because her condition was not improving, she borrowed some money and decided to go to a hospital far away from her home. In the hospital, treatment was commenced. On her third appointment in the hospital, she met a nurse who was from the same town with her. This made her to abandon her treatment. 6/30/2024 99 SEXUALLY TRANSMISSIBLE INFECTIONS AND CONSEQUENCES CONT’D. Health consequences Sexually transmissible infections can have a lot of implications on the reproductive health of an individual, especially in women, the consequences can be very serious. This is why STIs should be properly treated. In women, pelvic inflammatory disease (PID) can come with the following associated complications: - Infertility, ectopic pregnancy leading to maternal mortality; chronic pelvic pain, and increased possibility of subsequent pelvic infections. - Adverse pregnancy and neonatal outcomes have also been identified as a consequence of STIs; in pregnant women, the organism responsible for syphilis, Treponema pallidum can cross the placenta barrier and infect the foetus; the same is possible with gonorrhoea and Chlamydia trachomatis (trichomoniasis). 6/30/2024 100  SEXUALLY TRANSMISSIBLE INFECTIONS AND CONSEQUENCES CONT’D. Social consequences You should note in a country or an area where much value is attached to children, the social consequences of STI can be serious for a woman. Imagine a situation where improperly managed STI leads to infertility, a lot of sad things can happen to the woman: - She will be stigmatised - She can be abandoned or rejected by her husband Even when there is no problem of infertility, when there is STI, there may be conflicts arising between the couples. The friends and family members who provide support may start accusing the woman. There is mistrust which may lead to both psychological and emotional problems for the couple. 6/30/2024 101  SEXUALLY TRANSMISSIBLE INFECTIONS AND CONSEQUENCES CONT’D. Economic consequences STIs are not without some economic consequences. Handling the situation involves both direct and indirect costs. The direct costs are costs incurred in the process of treatment; diagnosis, screening and treatment can be very expensive. Because of the expensive screening cost, some communities have resorted to the use of syndrome management or presumptive therapy without laboratory screening. Some costs cannot be measured in Naira and Kobo, but that does not mean that they do not exist. Some of the indirect costs associated with STIs include: loss of productive life, the cost in infant morbidity, debility and mortality, increase in the economic burden placed on a society. 6/30/2024 102  STUDY MODULE 3: STUDY SESSION 2: Human Immunodeficiency Virus/Acquired Immune Deficiency Syndrome 6/30/2024 103 SEXUALLY TRANSMISSIBLE INFECTIONS AND CONSEQUENCES CONT’D. Introduction HIV is human immunodeficiency virus and AIDS is acquired immune deficiency syndrome. As a syndrome AIDS is a group of signs and symptoms resulting from the attack of the HIV on the body’s immune system. You must have heard that this is the worst epidemic so far and it affects every part of the globe. Its effect is estimated to that of four world wars put together and it still defies cure. Available drugs do not cure but prevent multiplication of the virus. 6/30/2024 104  HUMAN IMMUNODEFICIENCY VIRUS /ACQUIRED IMMUNE DEFICIENCY SYNDROME HIV/AIDS The human immuno-deficiency virus (HIV) is a retrovirus so called because this single stranded RNA (ssRNA) virus contains a polygene that codes for a reverse transcriptase. The HIV is causative agent of the acquired immune deficiency (AIDS) which is a pandemic that have spread to the whole world. In 1981, the Communicable Diseases Centre, Atlanta USA noted an increase in requests to use pentamidine for Pneumocystis carinii infection in previously well individuals who also suffered severe infections by other normally harmless microorganisms. These included Candida albicans (oesophagittis), mucocutaneous herpes simplex, toxoplasma (CNS infection) or pneumonia and cryptosporidial enteritis, and Kaposi’s sarcoma was often present. 6/30/2024 105  HIV/AIDS CONT’D. Such patients had evidence of impaired immune function as shown by skin test anergies and depletion of CD4 positive T– helper lymphocytes. This immunodeficiency syndrome appearing in an individual without a known cause, such as treatment with immunosuppressive drugs was referred to as “acquired immune deficiency syndrome” (AIDS). The signs and symptoms of acute HIV infection usually occur within days to weeks after initial exposure and last from a few days to more than 10 weeks (usually less than 14 days). Unfortunately, the syndrome is often undiagnosed or misdiagnosed because HIV antibodies are not usually detected during this early phase of infection. 6/30/2024 106  HIV/AIDS CONT’D. AIDS is a severe, life threatening syndrome which represents the late clinical state of infection with HIV. Invasion and destruction of helper T–Cells lead to suppression of the patient’s immune system. Helper T–Cells activate B cells to secrete antibodies and macrophages to destroy ingested microbes, but they also help activate cytotoxic T cells to kill infected target cells. The immune system of the HIV infected person is unable to produce antibodies in response to T–cell dependent antigens. Secondary infections caused by viruses, protozoans, bacteria and or fungi become systemic and caused death of the patients. AIDS patients die as a result of overwhelming infections caused by a variety of opportunistic pathogens. Previously considered to be a universally fatal disease, certain combinations of drugs referred to as cocktail are used in extending life of AIDS patients. 6/30/2024 107  HIV/AIDS CONT’D. 6/30/2024 108  TYPES OF HUMAN RETROVIRUSES HIV is classified as a retrovirus because it contains’ reverse transcriptase. It is a D type virus in the lentivirus family. Retroviruses are ribonucleic acid (RNA) viruses and in order to replicate they must make a deoxyribonucleic acid (DNA) copy of their RNA. It is the DNA genes that allow the virus to replicate. Like all viruses, HIV can replicate only inside cells, commandeering the cell machinery to replicate (reproduce). However, only HIV and other retroviruses, once inside the cell, use the enzyme called reverse transcriptase to convert their RNA into DNA which can be incorporated into the host cells’ gene. Infections of cultured T–cells with HIV usually result in cell death. 6/30/2024 109 TYPES OF HUMAN RETROVIRUSES CONT’D. The major antigenic types (HIV–1 and HIV–2) have been identified and are readily distinguished by differences in antibody reactivity to the envelope glycoproteins. The two HIV types share approximately 40% genetic identity. There is some disagreement about whether or not they are pathogens. Both apparently cause AIDS, but some researchers think that HIV–2 is less virulent in causing diseases. Different isolates of HIV–1 and HIV–2 exhibit considerable genomic variation and antigenic heterogeneity. This type of variation is observed in HIV isolates obtained from individuals over the course of their infection. HIV strains often display differences in replicative capacity and cytopathic effect /cytopathicity. 6/30/2024 110 TYPES OF HUMAN RETROVIRUSES CONT’D. Table 3.2.1: Human retroviruses Virus Characteristics HTLVI endemic in W. Indies and SW Japan transmission via milk, can cause adult T–Cell leukaemia and 1 associated myelopathy and tropical spastic apararesis, HTLV2 Uncommon, sporadic, occurrence, transmission via can use hairy T. Cell leukaemia HIV 1, Transmission via blood, sexual intercourses responsible for ARC, AIDS, AIDS dementia etc. HIV 2 is West Africans in origin. Closely related but antigenically different Human Causes foamy vacuolation in infected cells, little is of its occurrence or foamy pathogenic potential. virus Human Detected in placental tissues by electron microscopy by the presence of Placental reverse transcriptase Virus(es) Human Nucleic acid sequence representing endogenous retroviruses are common Genome in the vertebrate genome, often well-defined genetic loci, acquired during Viruses history, not expressed as infections virus; function unknown, perhaps should be regarded as mere DNA. 6/30/2024 111 TYPES OF HUMAN RETROVIRUSES CONT’D. In 1983, the causative virus of AIDS, HIV was isolated from blood lymphocytes and recognized as belonging to the Lentivirus (slow viruses) group of retroviruses related to similar agents in monkey and to similar virus in sheep and goats. The human placental and genome viruses are not known to be infectious agents. An increasing number of different strains of both HIV – 1 and HIV – 2 are being identified by molecular virology and by phenotyping in cell culture. Highly cytopathic and infectious strains of HIV – 1 have been identified in parts of Central Africa. Increases in virulence appear to be due to minor differences in the molecular structure of the virus. Some strains of HIV – 2 appear to cause few symptoms in those known to have been infected for many years. 6/30/2024 112 TYPES OF HUMAN RETROVIRUSES CONT’D. The molecular biological evidence through nucleic acid sequencing indicates that both HIV-1 and the closely related HIV-2, seen in West African probably arose from closely related primate viruses. HIV-1 may have been present in humans in Central African for many years but in the late 1970s it began to spread rapidly possibly with change of properties, as a result of increased transmission following major socio economic upheavals and migration of people from Central to East Africa such as female prostitutes and mobile male soldiers. 6/30/2024 113  THE STRUCTURE OF HIV The general structure of HIV is similar to that of Human T-cell Leukemia viruses (HTLV), the virus consists of an external lipid bilayer glycoprotein envelope (including envelopes proteins gp 120 and gp 41), an internal protein core (proteins p15, p17 and p24) a viral RNA complexed with reverse transcriptase. The HIV genome is approximately 10 kilobases which is larger than the HTLV. In addition to the structural gag, pol and env genes and regulator lat (analogous to HTLV rex) genes (nef, rif, vpu and vpr). HIV -2 does not have sequences for vpu but does encode a novel gene, vpx that is also found in the simian Immunodefiency virus. It is documented that the complete HIV particle consists of an envelope, a coat or capsid shell and core. 6/30/2024 114  THE STRUCTURE OF HIV The envelope is the membrane that surrounds the virus which is a lipid (fat bilayer), that is derived from the host proteins. Embedded in the envelope is the viral encoded glycoprotein (gp), gp41, bound to this is the outer glycoprotein knob gp120 molecules bind to specific molecules on the surface of the host cell called cluster designation 4 (CD4) receptors. The capsid is the protein coat that surrounds the core (viral genome) of the virus; it is made up of protein (P) P17 and P18 which the icosahedral symmetry. The viral core is the elongated inner mass of the virus which contains two identical single strands of viral RNA, structural protein, the enzyme reverse transcriptase and other enzymes. The main core protein is P25. Serological diagnosis of HIV is based on P24, P26 specific detection of antibodies to HIV and envelope proteins. 6/30/2024 115  THE STRUCTURE OF HIV 6/30/2024 116  REPLICATION IN HIV Viral replications are regulated by the products of the genes. The replication cycle is often halted after integration of the provirus, so that the infection remains latent in the cell. The lat and ref genes, for instance function as trans activating factors and can increase production of viral RNAs and proteins when latently infected cells are stimulated to differentiate (e.g. T-helper cell by antigen) or stimulated by infection with certain other viruses (e.g. HSV, cytomegalovirus) 6/30/2024 117  REPLICATION IN HIV The life cycle of HIV involves 8 steps namely: 1. Attachment / entry 2. Reverse transcription and DNA synthesis 3. Transport to the nucleus 4. Integration 5. Viral transcription 6. Viral protein synthesis 7. Assembly of virus 8. Release of virus 6/30/2024 118  REPLICATION IN HIV CONT’D. 1. Entry of HIV into Cells Infection typically begins when an HIV particle, which contains two copies of the HIV RNA, encounters a cell with a surface molecule called cluster designation 4 (CD4). Cells carrying this molecule are known as CD4 positive cells. One of the more of the virus pg120 molecules bind tightly to CD4 molecules(s) on the cells surface. The binding of gp 120 to CD4 results in conformational chance in the gp 120 molecule allowing it to bind to a second molecule on the cell surface known as co-receptor. The envelope of the virus and the cell membrane then fuse, leading to the entry of the virus into the cell. The gp41 of the envelope is critical to the fusion process. 6/30/2024 119  REPLICATION IN HIV CONT’D. Drugs that block either the binding or the fusion process are being developed and tested in clinical trials. Studies have identified multiple co-receptors for different types of HIV strains; these co- receptors are promising targets for new anti–HIV drugs, some of which are now being tested in pre-clinical and clinical studies. In the early stage of HIV diseases, most people harbour viruses that use, in addition to CD4, a receptor called CCR5 to enter their target cells. With disease progression, the spectrum of co-receptor usage expands in approximately 50 percent of patients to include other receptors, notably a molecule called CXCR4. Virus that utilizes CCR5 is called R5 HIV and virus that utilizes CXCR4 is called X4 HIV. 6/30/2024 120  REPLICATION IN HIV CONT’D. Although CD4+ T–cells appear to be the main target of HIV, other immune system cells with and without CD4 molecules on their surfaces are infected as well. Among these are long lived cells called monocytes and macrophages, which apparently can harbour large quantities of the virus without being killed, thus acting as reservoirs of HIV. CD4 T – cells also serve as important reservoir of HIV. A small proportion of these cells harbour HIV is a stable, inactive form. Normal immune processes may activate these cells resulting in the production of new HIV virions. Cell to cell spread of HIV also can occur through the CD4 – mediated fusion of an infected cell with an uninfected cell. 6/30/2024 121  REPLICATION IN HIV CONT’D. 2. Reverse Transcription In the cytoplasm of the cell HIV reverse transcriptase converts viral RNA into DNA, the nucleic acid form in which the cell carries the genes. Nine of the 15 antiviral drugs approved in the United States of America for treatment of people with HIV infection, AZT, ddC, ddI, d4T, 3TC nevirapine, delavirdineabacavir, and efavireng- work by interfering with this stage of the viral cycle. 3. Integration The newly made HIV DNA moves to the cell’s nucleus, where it is spliced into the list’s DNA with the help of HIV intergase. HIV DNA that enters the DNA of the cell is called a “provirus” intergase is an important stage for the development of new drugs. 6/30/2024 122  REPLICATION IN HIV CONT’D. 4. Viral Transcription For a provirus to produce new viruses, RNA copies must be made that can be read by the host cell’s protein making machinery. These copies are called messenger RNA (mRNA) and production of mRNA is called transcription, a process that involves the host cell’s own enzymes. Viral genes in concert with the cellular machinery control this process, the lat gene for example encodes a protein that accelerates transcription. Genomic RNA is also transcribed for later incorporation in the budding virion. Cytokines proteins involved in the normal regulation of the immune response may also regulate transcription. 6/30/2024 123  REPLICATION IN HIV CONT’D. Molecules such as tumour necrosis factor (TNF) alpha and interleuckin6 (IL – 6), secreted in elevated levels by the cells of HIV infected people may help to activate HIV proviruses. Other infections, by organisms such as Mycobacterium tuberculosis, may also enhance transcription by inducing the secretion of cytokines. 5. Translation After HIV mRNA is processed in the cell’s nucleus, it is transported to the cytoplasm. HIV proteins are critical to this process. For instance, a protein encoded by the rev gene allows mRNA encoding HIV, structural proteins to be transferred from the nucleus to the cytoplasm. Without the rev protein, structural proteins are not made. 6/30/2024 124  REPLICATION IN HIV CONT’D. In the cytoplasm, the virus coopts the cell’s protein making machinery including structures called ribosome to make long chains of viral proteins and enzymes using HIV mRNA as a template. This process is called translation. 6. Assembly and budding A newly made HIV co-receptor proteins, enzymes and genomic RNA gather just inside the cell’s membrane while the viral envelope proteins aggregate within the membrane. An immature viral particle forms and buds off from the cells, acquiring an envelope that includes both cellular and HIV proteins from the cells membrane. 6/30/2024 125  REPLICATION IN HIV CONT’D. During this part of the viral life cycle, the core of the virus is immature and the virus is not yet infectious. The long chains of the proteins and enzymes that make up the immature viral core are now cleaved into smaller pieces by a viral enzyme called protease. This step results in infectious viral particles. Drugs called inhibitors interfere with this step of the viral life cycle. Six of such drugs are saquinavir, ritonavir, indinavir, amprenavir, nelfinavir and lopinavir have been approved for marketing in the United States of America. 6/30/2024 126  REPLICATION IN HIV CONT’D. 6/30/2024 127  STUDY MODULE 3: STUDY SESSION 3 Epidemiology of HIV/AIDS 6/30/2024 128 GLOBAL EPIDEMIOLOGY OF HIV/AIDS Epidemiology of HIV/AIDS 2.1 HIV/AIDS global burden We have previously discussed that, the disease spreads through infected blood production and drug abuse, but overwhelmingly by sexual contact, predominantly between men and women. Women are more vulnerable to infection due to physiological and social reasons, and sex workers are far more likely than the population at large to be infected. But the sexual behaviour of men is largely responsible for spreading the disease. The study of HIV/AIDS general distribution pattern or spread as well as the total number of new cases is shown in the alarming figures enumerated below according to a report by the World Health Organisation (WHO). 6/30/2024 129  GLOBAL EPIDEMIOLOGY OF HIV/AIDS CONT’D. Table 1: Distribution of people within with HIV/AIDS S/no. Region Number of affected people 1 North America 1.2 million 2 Caribbean 300, 000 3 Western Europe 220,000 4 Eastern Europe &Central Asia 1.6 million 5 East Asia 870,000 6 South & South East Asia 7.4 million 7 Oceania 74,000 8 Sub-Sahara Africa 25.8 m illion 9 North Africa &Middle East 510,000 10 Latin America 1.8Million Total 39.774 Million 6/30/2024 130  GLOBAL EPIDEMIOLOGY OF HIV/AIDS CONT’D. 2.2 The United Nations’ view of HIV/AIDS Pandemic The United Nations has called AIDS the most devastating disease mankind has ever faced. AIDS is a worldwide catastrophe and the biggest plague in human history. The latest statistics tells you that around 40 Million people worldwide are HIV-positive. In sub-Saharan Africa, you have about 70% of that 40 Million people. Experts have made it known to us that 600,000 people, especially babies become infected each year. 6/30/2024 131 GLOBAL EPIDEMIOLOGY OF HIV/AIDS CONT’D. All the wars in the twentieth century resulted in 33 million deaths. But in just about 25 years of AIDS, we already have about 25 million people or more have died, 8,000 people die every day from HIV/AIDS in sub-Saharan Africa, from Nigeria to Cape Town, 6,000 people die daily from AIDS. The continent of America and the world were shocked when on September 11 of the year 2001, the world trade centre collapsed through terrorist’s attacks, but in Africa, the world trade centre collapses twice a day, in terms of the number of victims that die from AIDS in Africa. 6/30/2024 132  HIV IN NIGERIA 2.3 Epidemic of HIV in Nigeria You must have been informed that the spread of this virus in Nigeria is believed to have started in the 1980s with the first AIDS case reported in 1986. Nigeria is currently experiencing a generalised HIV prevalence persistently above 1% in pregnant women attending antenatal clinics since 1999. In 2003, it was estimated that 3.2-3.8 Million persons were living with HIV/AIDS in Nigeria, that statistics is not funny. You should believe that the statistics on HIV/AIDS in Nigeria is not a true picture of what is on ground but it is estimated that there could be 1 to 2 Million people in Lagos alone who are HIV positive. 6/30/2024 133  HIV IN NIGERIA CONT’D. The city of Lagos is also estimated to have the largest number of HIV positive victims than many cities in the world. It is also said that, in Lagos, commercial hawking of one’s body is a big factor in HIV/AIDS spread. Reports from the Federal Ministry of Health, the official HIV/AIDS prevalence rate in Nigeria between 2000 to 2005 is around 5.8%, and more recently, the 2007 health statistics indicates 4.4%, hopefully a steady and promising decline. 2.4 HIV sentinel surveillance The virus sentinel surveillance was established to monitor trend in the HIV epidemic and assess the impact of the response. 6/30/2024 134  HIV IN NIGERIA CONT’D. The survey was conducted from August 29 to November 26, 2005 to determine HIV prevalence among pregnant women attending antenatal clinics and also acquire data for estimating and projecting HIV Figures and trends in the general population. The 2005 sentinel survey involved 36,931 pregnant women attending antenatal clinics in 160 sites (86 urban and 74 rural) in 36 states and the management team was set up by the Federal Ministry of Health under the chairmanship of the Director of Public Health. The National Action Committee on AIDS (NACA), UN agencies, bilateral agencies and other stakeholders participated as members of the committee. 6/30/2024 135  HIV IN NIGERIA CONT’D. 2.5 Epidemiology of HIV/AIDS in Nigeria The prevalence of HIV among antenatal clinic clients after the 2005 sentinel survey was found to be 4.4%; it was 1.9% in 1991, 4.5% in 1996, and 5.8% in 2001. HIV epidemic in Nigeria has since extended beyond the high risk groups to the general population. Some parts of the country are worst affected than others but no state community is unaffected. All the states of Nigeria have a generalised epidemic (>1% among pregnant women). The epidemic in the country can be described as heterogeneous with various communities in different stages, some declining while others are still rising. From the result of the 2003 survey, it was estimated that 3.5 million people were living with HIV/AIDS in the country. 6/30/2024 136  HIV IN NIGERIA CONT’D. The report also showed that HIV was more prevalent in the 20-29 years age group in the urban areas and amongst persons with only primary and secondary school education. AIDS cases are becoming more visible in communities. Although AIDS case reporting has been characterised by under recognition, under reporting and delayed reporting, the number of reported cases has been on the increase especially since 1996. HIV prevalent rate among commercial sex workers in Nigeria has remained high and on the increase from 17.5% in 1991; through 22.5% in 1993, to 35.6% in 1995. This group constitutes an important reservoir of HIV infection for transmission to the general population through sexual networking well as the growth in prevalence among tuberculosis patients has remained relatively high 2.8% in 1991, 7.9% in 1993 13% in 1995 and 17% in 2000 (refer to Figures 1 to 3 and tables 1 to 4). 6/30/2024 137  HIV IN NIGERIA CONT’D. 2.5.1 HIV prevalence by State States in the North West and South West presents Lower HIV prevalence. High HIV prevalence is concentrated in Benue and adjoining State (see Figure 1). The state HIV prevalence range from 1.6% (Ekiti) to 10.0% (Benue) and the median prevalence was 4.0% (Abia). HIV prevalence among those in their first pregnancy was higher than those women with two or more pregnancies. The difference however was not statistically significant. HIV prevalence was also higher among women with no previous deliveries compared to women with one or more deliveries. 6/30/2024 138  HIV IN NIGERIA CONT’D. Fig 3.3.1: Geographical Distribution of HIV Prevalence by State (HSS 2005) HIV Prevalence by State (Nigeria 2005) 6/30/2024 139  HIV IN NIGERIA CONT’D. Fig 3.3.2: HIV prevalence by State, (HSS 2005) 6/30/2024 140  HIV IN NIGERIA CONT’D. Table 3.3.2: HIV Prevalence by Marital Status (HSS 2005) Marital status Single Married Others Total Sample size 1648 35074 182 36904 Number Positive 78 1528 16 1623 Prevalence (%) 4.8 4.4 8.8 4.4 Confidence interval 3.8-6.0 4.1-4.6 5.1-13.9 4.2-4.4 Table 3.3.3: HIV Prevalence by Educational Status Education status None Quranic Primary Secondary Higher Total Sample size 3757 5816 7768 13650 5911 36902 Number Positive 156 181 375 689 222 1623 Prevalence (%) 4.2 3.1 4.8 5.0 3.8 4.4 Confidence interval 3.5-4.9 2.7-3.6 4.4-5.3 4.7-5.4 3.3-4.3 4.2-4.6 6/30/2024 141  HIV IN NIGERIA CONT’D. Table 3.3.4: HIV prevalence by gravity and parity Marital status Sample size Sample size Prevalence Confidence (%) interval 1 9532 445 4.7 4.3-5.1 2 or more 27317 1177 4.3 4.1-4.6 Total 36851 1622 4.4 4.2-4.6 Parity 0 10332 490 4.7 4.3-5.2 1 7672 388 5.1 4.6-5.6 2 or more 18699 737 3.9 3.7-4.2 Total 36703 1615 4.4 4.2-4.5 6/30/2024 142  HIV IN NIGERIA CONT’D. Trend analysis Figure 3 shows the trend of HIV prevalence in Nigeria between 1991 and 2005, as reported from the HIV sentinel sero–surveillance cycle. There was a steady increase in HIV prevalence from 1.8% in 1991 to 5.8% in 2001 before a drop to 5.0% in 2003. The result for 2005 showed a further drop to 4.4%. 6/30/2024 143  HIV IN NIGERIA CONT’D. Figure 3.3.3: National HIV prevalence trend, 1991 – 2005, (HSS 2005) 6/30/2024 144  HIV IN NIGERIA CONT’D. Table 3.3.5: HIV Prevalence Trends by State from 1991 – 2005, (HSS 2005) States 91/92 93.94 95/96 1999 2001 2003 2005 Adamawa 0.3 1.3 5.3 5.0 4.5 7.6 4.2 Anambra 0.4 2.4 5.3 6.0 6.5 3.8 4.2 Benue 1.6 4.7 2.3 16.8 13.5 9.3 10.0 Borno 4.4 6.4 1.0 4.5 4.5 3.2 3.6 Cross River 0.0 4.1 1.4 5.8 8.0 12.0 6.1 Delta* 0.8 5.1 2.3 4.2 5.8 5.0 3.7 Edo 0.0 1.8 3.0 5.9 5.7 4.3 4.6 Enugu 1.3 3.7 10.2 4.7 5.2 4.9 6.5 Kaduna 0.9 4.6 7.5 11.6 5.6 6.0 5.6 Kano 0.0 0.4 2.5 4.3 3.8 4.1 3.4 Kwara 0.4 2.4 1.7 3.2 4.3 2.7 2.8 Lagos 1.9 6.8 - 6.7 3.5 4.7 3.3 Osun* 0.0 1.4 1.6 3.7 4.3 1.2 2.0 Oyo* 0.1 0.2 0.4 3.5 4.2 3.9 1.8 Plateau* 6.2 8.2 11.0 6.1 8.5 6.3 4.9 Sokoto 1.8 1.6 - 2.7 2.8 4.5 3.2 Abia ND ND ND 3.0 3.3 3.7 4.0 AkwaIbom ND ND ND 12.5 10.7 7.2 8.0 Bauchi NN ND ND 3.0 6.8 4.8 3.4 Bayelsa ND ND ND 4.3 7.2 4.0 3.8 6/30/2024 145  STUDY MODULE 3: STUDY SESSION 4 Testing For HIV and Results 6/30/2024 146  HIV TEST 2.1 The HIV Test When you perform a HIV test on a person, that procedure that tells if a person is HIV positive or negative by using a simple blood test, you can also perform the test by the use of saliva or urine. You have several methods to detect the infection. Most HIV test that are readily available and affordable do not actually test for the HIV virus but rather for the antibodies produced by the body in reaction to the HIV infection. It is important for you to note that even though HIV antibodies can be detected in the mouth and in urine, the virus cannot be transmitted from one person to another through saliva or urine. This is because there is not enough of the virus in saliva or urine to infect people this way. 6/30/2024 147  HIV TEST CONT’D. HIV needs to be present in very large quantities in order for a person to be infected. The only body fluids that contain enough HIV to be infectious are blood, semen, vaginal fluids and breast milk. There are tests which can detect the virus but they are very expensive to carry out and require rigorous procedure to carry it out. It is important to remember that the HIV test can only detect if a person has contracted the virus or not: 1. If a person has AIDS (only a doctor can make this diagnosis). 2. How the person became infected with HIV. 3. How long the person has been living with HIV. 4. Who infected the person? 6/30/2024 148  HIV TEST CONT’D. HIV test can be carried out in any reputable Medical institution/facility and various approved and regulated non- governmental organizations and laboratories across the country. When the HIV test is carried out typica