Veterinary epidemiology: introduction

It is important to note that the principles of veterinary epidemiology are identical to those of human epidemiology, with the exception that these principles are applied to animal populations rather than human populations. As such, veterinary and human epidemiology can be viewed as forms of the same discipline.

Epidemiology is principally concerned with the investigation of disease within populations (although the same principles are also applicable to investigation of other characteristics, such as animal welfare or productivity), and is based on the concept that disease often does not occur in a random fashion. That is, various characteristics of the animal, the pathogenic agent (or agents) and the environment interact in order to alter the probability of disease occurrence.

This view of disease at the population level differs from the approach traditionally taken by veterinary practitioners, who are principally concerned with the health status of the individual animal. However, in recent years, epidemiological principles are increasingly being applied in clinical practice, whether it be in the use of Evidence-Based Veterinary Medicine, in order to ensure that appropriate scientific methodology is applied in the treatment of individual animals, or through the use of aggregated animal data in the form of Herd Health Plans to advise on measures which can be applied at the farm level. Epidemiology is also an integral component of many Public Health and animal health programmes.

Patterns of disease occurrence can often give useful clues as to which factors may be affecting the health of the population, based on the principle that disease often does not occur randomly (that is, different factors interplay in order to produce disease). Epidemiologists therefore commonly investigate disease in terms of the following questions:

• Which animals are affected?
• Where are the affected animals located?
• When did the animals become affected?

This concept is often described as 'animal, place, time', which provides a very useful structure to follow in any epidemiological investigation. Epidemiologists will often work with members of other disciplines, such as economists, virologists, bacteriologists, ecologists, pharmacologists, pathologists and politicians when evaluating appropriate methods of investigating and/or controlling diseases in populations.