Scope of Epidemiology

Epidemiology

Epidemiology is the study of disease in populations and of factors that determine its occurrence

Determinants

Determinants include:

• Risk factors- (promote disease)
• Deterrent – (prevent disease)

Uses of epidemiology

There are five objectives of epidemiology:

• Determination of the origin of a disease whose cause in known
• Investigation and control of a disease whose cause is unknown
• Acquisition of ecology and natural history of disease
• Planning, monitoring and assessment of disease control programmes
• Assessment of the economic effects of a disease

Epidemiologist

Disease with known cause

• Disease with a known cause can be diagnosed precisely (clinical signs, lab aid)
• To determine that “why an outbreak occurred” OR Why has the number of cases increased?
• To find the reason is important in limiting spread and eradication of diseases

An example:

• Increased number of actinobacillosis cases in a group of cattle might be associated with grazing a particular pasture of 'burnt-off' stubble. Such an occurrence could be associated with an increase in abrasions of the buccal mucosae, caused by abrasive ash, which could increase the animals' susceptibility to infection with Actinobacillus lignieresi

Disease with unknown or poorly understood cause:

• Epidemiological studies are also used to identify causes of disease (many of which are multifactor and initially poorly understood) so that the most appropriate disease control echniques can be applied.

An example

• Developed bovine spongiform encephalopathy following consumption of feedstuffs containing meat and bone meal contaminated with a scrapie-like agent.

Ecology and natural history of a disease:

• Host: An animal that can become infected with an infectious agent is a host of that agent.
• Natural History: Hosts and agents exist in communities that include other organisms, all of which live in particular environments. The aggregate of all facts relating to animals and plants is their natural history.
• Ecology: Related communities and their environments are termed ecosystems. The study of ecosystems is ecology.

Examples:

• Knowledge of non-infectious diseases can be obtained by studying the ecosystems and the associated physical features with which affected animals are related
• Environment of an ecosystem affects the survival rate of infectious agents and of their hosts. Thus, infection with the helminth Fasciola hepatica is a serious problem only in poorly drained areas, because the parasite spends part of its life-cycle in a snail that requires moist surroundings.

Planning, monitoring and assessment of disease control programmes:

Knowledge of the

• Amount of the disease in that population
• Factor associated with its occurrence
• Facilities required controlling the disease
• Costs and benefits involved
• Routine collection of data on disease in population (monitoring and surveillance)

Economic effects of a disease and of its control:

• The cost of the control of disease in the livestock industry must to balance against the economic loss attributable to the diseases.

Example: 

• If 15% of the cows in a herd were affected by mastitis, productivity would be severely affected and a control programme would be likely to reap financial benefit. On the other hand, if less than 1 % of the herd were affected, the cost of further reduction of the disease might not result in a sufficient increase in productivity to pay for the control programme.