An epizootic (from Greek epi for upon and zoon for animal) is a disease event in an animal population similar to an epidemic in humans. It may be restricted to a specific locale (outbreak), general (epizootic) or widespread (panzootic). Examples of epizootic disease include avian influenza, swine fever and foot and mouth disease.
Defining an epizootic can be subjective; it is based upon the number of new cases in a given animal population, during a given period, and must be judged to be a rate that substantially exceeds what is expected based on recent experience (i.e. a sharp elevation in the incidence rate). Because it is based on what is “expected” or thought normal, a few cases of a very rare disease (like a transmissible spongiform encephalopathy outbreak in a cervid population) might be classified as an “epizootic”, while many cases of a common disease (like lymphocystis in esocids) would not.
Common diseases that occur at a constant but relatively high rate in the population are said to be “enzootic” (cf. the epidemiological meaning of “endemic” for human diseases). An example of an enzootic disease would be the influenza virus in some bird populations[1] or, at a lower incidence, the Type IVb strain of viral hemorrhagic septicemia in certain Atlantic fish populations.
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