ANALYSIS OF HUMORAL IMMUNE-RESPONSE IN CHICKENS AFTER INOCULATION WITH CRYPTOSPORIDIUM-BAILEYI OR CRYPTOSPORIDIUM-PARVUM

White leghorn chickens aged 14 days were orally inoculated with 1 x 10 (6) oocysts of Cryptosporidium baileyi or C. parvum to compare the spe cific immune responses. Cross-reactions were evaluated using homologou s or heterologous antigens in enzyme-linked immunosorbent assay (ELISA ) and Western blot to determine the occurrence of an antigenic homolog y between these two species. Blood, bile, whole intestine, bursa of Fa bricius, and feces were collected daily from the day of inoculation (d ay 0) to day 22 postinoculation (PI). Eight control chickens remained negative up to day 22 PI. Chickens inoculated with C. baileyi did not express clinical symptoms but shed oocysts from days 6 to 21 PI. Chick ens inoculated with C. parvum exhibited no clinical signs, no oocysts in feces, and no developmental stages of the parasite. However, a spec ific immune response to both antigens appeared on day 3 PI. ELISA usin g homologous or heterologous antigens showed that anti-C. baileyi and anti-C parvum antibodies in serum or bile were detectable using C. bai leyi or C. parvum oocysts as antigen, but the intensity of the respons e was significantly higher when C. baileyi was used. Cross-reactions i n immunoblot analysis confirmed ELISA results, revealing a greater num ber of bands using C. baileyi as antigen but showing that epitopes rec ognized on the protein with a molecular weight of 15,000-17,000 were d ifferent.