Studies on cryptosporidiosis of birds look back only about 10 years of
history. The best known species is C. baileyi, occurring in the intes
tine, bursa of Fabricius, cloaca and respiratory tract of domestic chi
ckens and other avian species. Endogenous stages multiply in the micro
villous border of epithelial cells, resulting in a 2-3 week oocyst she
dding. The occurrence is often complicated with non-infectious and inf
ectious factors. Concurrent C. baileyi infection with chicken anaemia
virus was recently detected in Hungary. The prevalence of avian crypto
sporidiosis is certainly widespread but its zoonotic impact has not be
en proved. The high resistance to many drugs so far tested, against ve
rtebrate Cryptospordium species features also C. baileyi.