The Collaborative International Dictionary of English v.0.48:

Enzootic \En`zo*["o]t"ic\ ([e^]n`z[-o]*[o^]t"[i^]k), a. [Gr. 'en
   in + zw^,on an animal: cf. F. enzo["o]tique.]
   Afflicting animals; -- used of a disease affecting the
   animals of a district. It corresponds to an endemic disease
   among men.
   [1913 Webster]

WordNet (r) 3.0 (2006):

enzootic
    adj 1: of a disease that is constantly present in an animal
           community but only occurs in a small number of cases