[The black-headed gull (Larus ridibundus L.), a new host for Cryptosporidium baileyi (Apicomplexa: Cryptosporidiidae)].

Black-headed full (L. ridibundus L.) represents a new host of C. baileyi Current, Upton and Haynes, 1986. In 1991-1992 during the months of May-July six localities in three regions of the Czech Republic were studied by examining in total 264 not flying gull chicks (4-30 days of age), applying the methods after Pavlásek (1987a, b, 1991). Cryptosporidia were found in gulls in all localities and spontaneous infection during the period under study occurred in 27.5-100% of birds (Tab. II, Fig. 1). The size of oocysts was 6.2-6.4 by 4.8-5.8 microns with means of 6.4 by 4.9 microns. The oocyst index (width/length) was 0.75-0.93 with means of 0.77. C. baileyi infection was demonstrated in 22 out of 24 dead gull chicks submitted to autopsy. From two localities total 15 gulls were killed, the examination of which revealed oocyst occurring in masses in the fluid from cloacal washes. Asexual and sexual endogenous developmental stages, including C. baileyi oocysts, in all birds undergoing autopsy were localized in caudal part of colon (1-2 cm from opening into cloaca) and in the cloaca. Findings of cryptosporidia were very frequent, above all, in the bursa Fabricii. In two dead and six with snoring disease, subsequently killed gull chicks, respiratory form of infection was demonstrated with simultaneous proof of endogenous developmental stages including oocysts in smears of mucous epithelium of sinus infraorbitalis, larynx, trachea and bronchi using the Giemsa stain after fixation with absolute methanol. An experimental transmission of infection by isolates of C. baileyi oocysts from gulls to five 4-day chicks (Gallus gallus f. domestica) using the dosis of 5 x 10(5) oocysts/chick was successful. The prepatent period lasted 4 days. On day 3 and 6 after infection two chicks died. The developmental stages of the protozoon were found in the lower part of colon, in cloaca and in bursa Fabricii. In chicks dead on day 6 after infection asexual stages of cryptosporidia were found in trachea and in bronchi. One chick survived the infection and excretion of oocyst (patent period) lasted 14 days. In this bird cloacal, bursal as well as respiratory form of C. baileyi infection was found. Control chicks were negative during the observation of 30 days. Oocysts from gulls do not lose their viability even after 8-month storage in the 2.5% solution of K2Cr2O7 at the temperature of 4 degrees C.(ABSTRACT TRUNCATED AT 400 WORDS)