medicine note

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Epidemiology and Preventive Veterinary Medicine VEP-411 Cr. Hr. 1+1=2
Preventive Veterinary Medicine: Is that branch of veterinary medicine which deals with the diseases
of infectious origin and of contagious nature, its occurrence among animal population and its
prevention and control. It embraces the etiology, epidemiology, pathogenesis, confirmatory diagnosis
and curative measures of the individual animals as well control of infection in the animal community.
Preventive medicine is primarily is aimed at necessary control and prevention of diseases in a flock or
herd. It is also known as herd health medicine.
Epidemiology:
Epidemiology has its origin in the idea, first expressed over 2000 years ago by Hippocrates and
others, those environment factors can influences the occurrence of disease. Over the years there have
been many definitions of epidemiology. Some definitions are as follows.
Greek: EPI - Upon
DEMOS - People
LOGOS - Study of, Body 0r Knowledge
• Generally occurs when new cases of a certain disease, in a given human population, and during a
given period.
• Epidemiologists often consider the term outbreak to be synonymous to epidemic.
DEFINITIONS OF EPIDEMIOLOGY
The study of the distribution and determinants of disease frequency in human populations. (1970)
The study of the distribution and determinants of health-related states or events in specified populations,
and the application of this study to control of health problems. (1988)
THE BRANCH OF MEDICAL SCIENCE WHICH TREATS EPIDEMICS. (Oxford English Dictionary)
EPIDEMIOLOGY IS THE STUDY OF "EPIDEMICS" AND THEIR PREVENTION. Kuller LH: American
J. of Epidemiology 1991;134:1051)
THE STUDY OF THE OCCURRENCE OF ILLNESS. (Anderson G. In: Rothman KJ: Modern
Epidemiology).
The underlying premise of epidemiology is that disease not occur at random, but rather in patterns that
reflect the operation of underlying factors.

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Now a days it is defined as:
Science concerned with the study of the factors, determining and influencing the frequency of distribution
of disease, injury orother health related events and their causes in a defined human population for the
purpose of establishing programs to prevent and control their development and spread.
Epidemiology is not limited to the study of disease, it may also be used to determine what keeps a
population healthy. Epidemiology may thus be considered as the study of health and disease in
populations. Epidemiology deals with naturally or spontaneously occurring rather than experimentally
induced conditions.
Thus epidemiology is concerned with the population rather than the individual, however, an
understanding of health and disease in populations is fundamental to medical decision-making in the
individual. It is with the circumstances under which diseases occur, where diseases tend to flourish and
where they do not. It is also concerned with the epidemiology of the disease with mode of transmission of
these agents, with environment conditions that permit or emphasis and resistance of the host. The special
contribution of epidemiology is providing information describing the frequency and distribution of health
and disease, identifying factors influencing the occurrence and severity of disease in the population of
concern (in its natural settings), and quantitating the interrelationships between health and disease.
Objectives:
1. Distinguish between the concepts of disease and health.
2. Define and understand the uses of epidemiology.
3. Distinguish between public health, epidemiology, and clinical medicine.
4. Recognize major historical contributions in epidemiology.
5. Understand the inter-disciplinary nature of epidemiology.
6. Understand the “epidemiologic transition” of causes of mortality from developing to developed
countries.
7. Understand practical, ethical, and professional issues in conducting epidemiologic research.
8. Recognize the role of Institutional Review Boards in overseeing the conduct of epidemiologic
research.
9. Understand the natural history of disease progression.
10. Distinguish between primary, secondary, and tertiary levels of disease prevention.

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BASIC CONCEPTS IN EPIDEMIOLOGY
• agent
• host
• environment
Agent: an animate or inanimate factor that must be present or lacking for a disease or condition to
develop.
• Host: a living species (human or animal) capable of being infected or affected by an agent.
• Environment: all that is internal or external to a given host or agent and that is influenced and
influences the host and/or agent.
Scope Of Epidemiology
• Epidemiology studies the determinants of health-related states and events.
• Epidemiology studies the distribution of health-related states and events; the distribution is
viewed in three epidemiological dimensions of time, place and person.
• Scope: Scope means opportunity for unhampered motion, activity , or thought, or extend of
appications.
• Evaluation of usefulness and effectiveness of new or innovative techniques.
• Conducting epidemiological researches on changing trends in the distribution and determinants of
health and illness.
AIMS OF EPIDEMIOLOGY
• Aim: The word aim means to direct towards an intended target. The aim of epidemiology is to
protect, promote and restore health of man and animals efficiently.
USES OF EPIDEMIOLOGY
• to study the occurrence of diseases in a population.
• to study historically the rise and fall of disease in the population.
• to identify health problems in animal.
• quantifying a health problems in the herd.
• quantifying a health problems in the community

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• to diagnose the health of the community
• Searching for cause and risk factors
• to identify determinants of disease
• to estimate individual risks and chances
• to plan health services
• to evaluate intervention measures
• to complete Natural History of Diseases.
• to identify syndrome.
• to forecast future disease trends.
Methods of Epidemiology/ methods of epidemiological studies:
Methods of epidemiological study may be classified into different stage for the study of disease
process in populations.
1. Descriptive epidemiology:
This is the first step of investigation and consists of the collections of data on the disease, the host
population, and the geographical distribution and temporal course of the disease. Descriptive
epidemiology means making observation in the field to gain as much as information as possible
on prevalence, distribution, duration of the host species involves, the population affected or at
risk, the possible agent, environment or host determinants of the disease phenomenon or event:
and a mode of transmission ( in the case of infections). The questions include: what is the event
or phenomenon? which are the animals involved?, when did it take place?, where did it take
place? Descriptive epidemiological studies do not have control over the circumstances. Thus it is
an observational study in the field in its natural setting.
2. Analytical epidemiology
Is the analysis of available data for the detection both of the general and the disease specific
causes? It tries to answer how and why these people were affected. The epidemiologists
determine the role of various risk factors in causing the problem. It draws statistical inferences
about disease occurrence in population and possible causal associations.
Application of epidemiology:
Epidemiology has following principal applications.
1. Investigative or diagnostic discipline
2. Clinical research

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3. Evaluation of medical controversy
4. Directed action against diseases.
1. Investigation or diagnostic discipline
Epidemiology serves as the investigation or diagnostic discipline for population or herd medicine.
The epidemiological approach to diagnosis is a holistic one. Its basic unit of concern- its patients-
is the herd, the flock rather than the single sick and animal. The population unit includes the well
animals as well as individual patients dead ones. Epidemiological diagnosis is considered less
with individual patients per se than with the frequency of disease events and death in a
population, along with their patterns and probability of occurrence whereas clinical diagnosis
gains knowledge necessary for the treatment and recovery of the sick individual. On the other
hand pathological diagnosis acquire knowledge to treat future cases. However, the diagnostic
disciplines- clinical diagnosis, pathology and epidemiology complement one another; and their
distinctly different tools may be applied sequentially to the solution of diagnostic problem,
describing disease and investigating their causes although use of all three may not be necessary in
each instances.
Diagnostic uses of epidemiology have two interrelated avenues for their initial expression;
intensive follow up and surveillance. As the name implies intensive follow up is a detailed
multifaceted study of seemingly relvent aspect of a disease event in a population unit. One of its
commonest forms is the out-break investigation. Surveillanve is the opposite follow-up. As the
technically defined surveillance is an active disease accounting process, ie. a broad overall,
organized approach to the collection, collation, analysis, expression and dissemination of data
about disease in large or small populations. Some like to call it “information for action”.
2. Clinical Research
Clinical epidemiological findings complement laboratory studies of experimentally induced
disease in exploring causal relationship in disease. Some clinical issues cannot be approached in
the laboratory. For example; the effectiveness of treatments must be measured in clinical
scenarios, clinical epidemiology also provides a means to study rare conditions or complication of
disease that would be difficult to induce experimentally.
3. Evaluate medical controversy/ claim
Medicine, like all of science, operate under system whereby hypotheses practices are continually
being challenged and updated by the collective experience of researches and practitioners are
discovered and disease mechanisms are finally understood. Many medical procedures are on
uncertain ground , sure to be replaced over time. Our current knowledge is continually tested and
updated. The reports themselves are subject to bias, methodological errors and invalid
assumptions. Consequently, must continually monitor and critically evaluate the medical
reports/claims to determine what medical claims are worthy of considerations. Epidemiology
provides the tools for critical evaluation of medical claims.

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4. Directed Action against diseases
The directed action of epidemiology against disease include; 1) studies on the nature and extent
of the disease problems present in a given population; 2) studies on the overall behavior of
particular diseases in different populatins, with investigation of their determinants and patterns of
occurrence; 3) planning and evaluation of efforts to prevent or control diseases; 4) research on
new methods or approaches for the investigation and control of diseases.
Veterinary Epidemiology
 Veterinary epidemiology deals with the investigation of diseases, productivity and animal welfare
in populations. It is used to describe the frequency of disease occurrence and how disease,
productivity and welfare are affected by the interaction of different factors or determinants. This
information is then used to manipulate such determinants in order to reduce the frequency of
disease occurrence.
 Veterinary epidemiology is a holistic approach aimed at co-ordinating the use of different
scientific disciplines and techniques during an investigation of disease or impaired productivity or
welfare. The field of veterinary epidemiology can be divided into different components.
 One of its essential foundations is the collection of data, which then has to be analysed using
qualitative or quantitative approaches in order to formulate causal hypotheses. As part of the
quantitative approach to epidemiological analysis, epidemiological investigations involving field
studies or surveys are being conducted and models of epidemiological problems can be
developed. The ultimate goal is to control a disease problem, reduce productivity losses and
improve animal welfare.
Some terminology
• Carrier: infected person or animal which harbors infectious agents in absence of clinical l
symptoms and serves as potential source of infection of others.
• Case: animal or human being having a particular diseases or health disorders.
• Control: measures to reduce incidence or prevalence of disease or infections in man or animal.
• Disease: a condition of body, organ or part in which its function are impaired or affected.
• Endemic: constant presence of a disease or infections or an infectious agent within a geographical
area without importation from outside.
• Epidemic: Occurrence of a disease in a community clearly in excess of normal expectations for
that populations based on past experience.
• Pandemic: Disease spreading over wide geographical area involving several species, countries
and continents.

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• Environment: Aggregate of all external conditions and influences affecting the life and
development of an organisms and its behaviour in the society.
• Eradication: Total removal or elimination of a disease or a etiological agent from a region.
Ecological Concept ofepidemiology