EPIDEMIOLOGICAL METHODS -MOLECULAR, SEROLOGICAL

EPIDEMIOLOGY

1. EPIDEMIOLOGICAL METHODS EXPERIMENTAL, THEORETICAL, SEROLOGICAL AND MOLECULAR SUBMITTED TO : Dr. B. SRINU ASSISTANT PROFESSOR & HEAD DEPARTMENT OF VETERINARY PUBLIC HEALTH AND EPIDEMIOLOGY SUBMITTED BY : G.NAVEEN WV/2022-13

2. EPIDEMIOLOGY : “The study of the occurrence and distribution of health related events ,states, and processes in specified populations, including the study of the determinants influencing such processes, and the application of this knowledge to control relevant health problems”. The epidemiology is expression of the wide ranging subject matter. The diseases included in this matter increased from those which occur in epidemics to include those infectious diseases which are endemic in nature ,and more recently chronic diseases ,accidents and mental health.

3. Modern epidemiology has also taken within its scope the study of health-related states, events and “facts of life ” occurring in human population. Epidemiology, like the public health itself, is often more concerned with the well-being of society as a whole, than with the well-being of individual.

4. Aims of epidemiology: According to the International Epidemiology Association (IEA ), the aim of epidemiology has: To describe the distribution and magnitude of health and disease problems in animal population. To identify etiological factors in the pathogenesis of disease. To provide the data essential to the planning ,implementation and evaluation of services for the prevention, control and treatment of disease. To minimize or eradicate the disease or health problems and their consequences. To minimize the chances of disease occurrence in future.

5. EPIDEMIOLOGIC METHODS: Epidemiological studies can be classified : Experimental methods Theoretical methods Serological methods Molecular methods

6. Experimental Epidemiology: The experimental studies have become a major area of epidemiological studies. They may be conducted in animals or human beings In the 1920 “experimental epidemiology’’ meant the study of epidemics among colonies of experimental animals such as rats and mice. The experimental epidemiology will observe and analyze data by conducting experiments. Most of the research activities in veterinary field deals with experimental observations compared to the descriptive observations made in natural cases in human activities.

7. Aims of experimental epidemiology: To provide “scientific proof’’ of etiological factors which may permit the modification or control of those studies. To provide a method for measuring the effectiveness To provide the efficiency of health services for prevention, control and treatment of disease and improve the health of community.

8. Animal studies: At the beginning of this century, Webster in united states and Topley,Wilson and Greenwood in England had carried out classical animal experiment. Advantages: Experimental animals can be breed in laboratories and manipulated easily according to the wishes of the investigator. More important point is that they multiply rapidly and enable the investigator to carry out certain experiments.

9. Human experiments : Human experiments will always be needed to investigate disease etiology and to evaluate the preventive and therapeutic measures. These studies are even more essential in the investigation of diseases that cannot be reproduce in animals. Ex: JAMES LIND EDWARD JENNER GOLDBERGER’S EXPERIMENT. Therefore, before launching human experiments, the benefits of the experiment have to be weighed against risk involved.

10. Experimental studies are of two types : Randomized controlled trials ( those involving a process of random allocation). Non-randomized or “non-experimental’’ trials(those departing from strict randomization for practical purposes, but in such a manner that non-randomization does not seriously affect the theoretical basis of conclusions).

11. RANDOMIZED CONTROL TRIALS An important advance in this field has been the development of an assessment method known as(RCT). It is really an epidemiologic experiment. Since its introduction.The RCT as questioned the validity of such widely used treatments as oral hypoglycemic agents, varicose vein stripping,tonsillectomy hospitalization of all patients with myocardial infarction, multiphasic screening and toxicity. For new programmes are new therapies,the RCT is the No.1 method of evaluation.

12. The basic steps in conducting a RCT: THE PROTOCOL SELECTING REFERENCE AND EXPERIMENTAL POPULATION RANDOMIZATION MANIPULATION FOLLOW-UP ASSESSMENT

13. 1.THE PROTOCOL: It specifies : Aims &objective of study. Questions to be answered.Criteria for selection of study and control groups. Size of sample, treatment to be applied,standardization of working procedures. Schedules and responsibilites of the parties involved. Aim: Preventing bias and to reduce the source of errors in the study. Some times it is useful to have short test to run of the protocol to see any flaws known as preliminary test runs.

14. 2.selecting reference & experimental population: Reference or target population: It is the population to which the findings of the trial are expected to be applicable .A reference population may be as mankind in specific age, sex, occupation or social groups. Experiment or study population: It is derived from the reference population. It is actual population that participates in experimental study. Participants must fullfill three criterias … Must give informed consent Should be representative of the population. Should be eligible for the trial.

15. 3.randomization: It is a statistical procedure by which participants allocated in to study and control groups. It is a heart of RCT. It will give greatest confidence that the groups are comparable so that ’’like can be compared with like’’. Randomization is done only after the participants entered the study ,that is after having been qualified for the trials. Randomization best done by using a table of random numbers(simple random sample) to eliminate personal selection of unconscious bias in taking out the sample.

16. 4.Manipulation : After selection of study &control group, intervene the study group by deliberate application ( vaccine, drug) as laid down in protocol. This manipulation creates an independent variable ( drug, vaccine ) whose effect is then determined by measurement of the final outcome, which constitutes the dependent variable ( incidence of disease, survival time. )

17. 5.Follow -up This implies examination of the experimental & control group subjects at defined intervals of time in a standard manner, with equal intensity, under the same given circumstances, in the same time frame till final assessment of outcomes. Attrition : some cases losses to follow-up due death, migration, loss of interest. If the attrition is substantial, it may be difficult to generalized the results to references population.

18. 6.Assessment: Positive result: Benefits of experiment measures reduced incidence or severity of disease. Negative result: Severity and frequency of side-effects and complications, if any including death.

19. Advantages: Random assignment eliminates selection bias, ensuring groups are comparable. Provide strong evidence of cause-effect relationships. With proper sample sizes, RCTs are highly reliable in detecting difference. Disadvantages: requires significant resources and extended timelines. Participants dropping out can affect results. Randomization may deny some participants access to potentially beneficial treatments.

20. NON-RANDOMIZED TRIALS: Due to ethical, administrative, cost it is not always possible to resort to RCT. As there is no randomisation , degree of comparability will be low and chances of spurious results will be high. Example of non-randomized trials: 1.uncontrolled trials: Trials with no comparision groups. Useful to know whether specific therapy is valuable for particular disease, to determine the appropriate dose, to investigate adverse reaction.

21. 2. natural experiments: Where experimental studies are not possible in human beings, some natural circumstances mimics as experiments. 3.Before and after comparision studies: This community trials fall into 2 distinct groups. Before & after comparision studies without control. Before & after comparision studies with control.

22. Advantages: Easier to implement and less costly than RCTs. Participants are not randomized, which may be more acceptable in certain cases. Ensure temporal relationship between exposure and outcomes. Disadvantages: Lack of randomization increases the risk of selection bias. More difficult to establish cause-effects relationships. Results may be harder to generalize or interpret accurately.

23. Difference between RCT AND NRCT: Aspects RCT NRCT Bias control Minimizes bias High risk of bias Causality Strong evidence Weaker evidence Cost High Lower Feasibility Complex Simpler Applicability Limited generalizability Better real-world evidence Ethical concerns Randomization issues Less controversial

24. THEORETICAL EPIDEMIOLOGY: Mathematical models are used to study the disease and these models attempt to stimulate natural patterns of disease occurrence. Helps design effective public health policies and control strategies. Provide insights into how disease spread and persist and explore how pathogens evolve in response to host defenses, treatments, and populations changes. Stimulation modelling is an area which will become more important as part of decision support in agriculture in the future. Models are used to represent dynamic processes or systems and stimulate their behaviour through time

25. There are two main groups of stimulation models, those based on mathematical equation which are called deterministic models. Those based on the probabilistic sampling of distribution which are called stochastic models The tools used for the development of such models include computerised spreadsheets which allow non-programmer to construct simple models. Advantages: Models can forecast disease outbreaks, helping policymakers prepare and allocate resource efficiently. Provides insights into how disease spread, persist, and interact with host populations and environment. Provide quantitative evidence for strategies like vaccination coverage, treatment protocols, or containment measures.

26. Disadvantages: Accuracy depends on the quality and availability of epidemiological, demographic, and behavioral data. Models may not account for unquantifiable factors such as cultural behaviors or unpredictable events. Results may be too technical or abstract for non-experts, complicating their use in public health planning.

27. SEROLOGICAL EPIDEMIOLOGY: It is a branch of epidemiology that uses serological ( blood serum ) tests to study the distribution, prevalence, and dynamics of disease in populations. It focuses on measuring antibodies, antigens, or other immune markers to assess past exposure, immunity levels, and infection rates. A range of constituents of serum can be measured, including minerals, trace elements, enzymes and hormones. One of the main constituents that is frequently measured is the specific antibodies activity of immunoglobulins , and investigation of antibodies that commonly understood in serology.

28. The serological diagnosis of disease based on the detection of circulating antibodies is one of the techniques available for the identification of current and previous exposure to infectious agents. Monitoring the spread of infectious disease like COVID-19 HIV, hepatitis or dengue. Evaluating vaccine efficacy by measuring antibody responses. Identify high-risk groups or regions with low immunity levels. Investigating animal-to-human transmission of diseases like rabies or avian influenza.

29. Advantages: Detects infections even in individuals even in individuals who no longer have active symptoms or pathogens. Helps estimate herd immunity and guide vaccination campaigns Provide historical data on disease exposure over time. Blood sample are relatively easy to collect and store. Disadvantages: timing of testing is critical, as antibody levels vary during the infection cycle. Differentiating between natural infection and vaccine-induced immunity can be challenging.

30. Molecular epidemiology: It is a field of epidemiology that integrates molecular biology techniques into traditional epidemiological studies to understand the distribution, determinants, and dynamic of disease. It focuses on analyzing genetics, biochemical, and molecular marker to identify risk factors, trace disease origins and study mechanisms at molecular level. It is a molecular indicator such as DNA, RNA, proteins, metabolites, or specific mutations that reveal information about exposure, susceptibility, or disease progression.

31. Using molecular tools to study the genetic material of pathogens to trace transmission, mutations, and evolution. Understanding how host genetic factors interact with pathogens to influence susceptibility and disease outcomes. Identifying genetic mutations or biomarkers linked to disease like cancer, diabetes, or infectious diseases. Identifying source of outbreaks and pattern of antimicrobial resistance. Informing targeted therapies and prevention strategies based on molecular profiles. Developing precision vaccines or treatments.

32. Advantages: Provide detailed insights into disease mechanisms and risk factors. Accurately distinguishes between strains or variants of infection agents. Facilitates the development of precision public health strategies and treatments. Disadvantages: Complex molecular data can be difficult to analyze and contextualize. Findings from specific populations may not apply universally. High-throughput molecular studies demand extensive computational and laboratory resources.