Inepizoology, anepizootic (orepizoötic, fromGreek:epi- "upon" +zoon "animal") is adisease event in a nonhumananimal population analogous to anepidemic in humans. An epizootic disease (orepizooty) may occur in a specific locale (an "outbreak"), more generally (an "epizootic"), or become widespread ("panzootic"). Highpopulation density is a major contributing factor to epizootics. Theaquacultureindustry is sometimes plagued by disease because of the large number offish confined to a small area.
Defining and declaring an epizootic can be subjective; health authorities evaluate the number of new cases in a given animal population during a given period, and estimate a rate of spread that substantially exceeds what they might expect based on recent experience (i.e. a sharp elevation in theincidence rate). Because the judgement is based on what is "expected" or thought normal, a few cases of a very rare disease (like atransmissible spongiform encephalopathy outbreak in acervid population) might be classified as an "epizootic", while many cases of a common disease (likelymphocystis inesocids) would not.
Common diseases that occur at a constant but relatively high rate in the population class as "enzootic" (compare the epidemiological meaning of "endemic" for human diseases). An example of an enzootic disease would be theinfluenza virus in some bird populations[1] or, at a lower incidence, the Type IVb strain ofviral hemorrhagic septicemia in certain Atlantic fish populations.[2][3]
An example of an epizootic was the 1990 outbreak ofNewcastle disease virus indouble-crested cormorant colonies on theGreat Lakes that resulted in the death of some 10,000 birds.[4][5]
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