Epizootic


In epizoology, an epizootic is a disease event in a nonhuman animal population analogous to an epidemic in humans. An epizootic may be restricted to a specific locale, general, or widespread. High population density is a major contributing factor to epizootics. Aquaculture is an industry sometimes plagued by disease because of the large number of fish confined to a small area.
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. Because it is based on what is "expected" or thought normal, a few cases of a very rare disease might be classified as an "epizootic", while many cases of a common disease would not.
Common diseases that occur at a constant but relatively high rate in the population are said to be "enzootic". An example of an enzootic disease would be the influenza virus in some bird populations or, at a lower incidence, the Type IVb strain of VHS in certain Atlantic fish populations.
An example of an epizootic would be the 1990 outbreak of Newcastle disease virus in double-crested cormorant colonies on the Great Lakes that resulted in the death of some 10,000 birds.