In order to study the possibility of immunization against Cryptosporidium baileyi with extracted crude antigen, Arbor Acres chickens were injected intramuscularly with 80 μg of C. baileyi oocyst-derived proteins (uninfected immunized, UI) or inoculated orally with 8 x 105 viable C. baileyi oocysts (infected control, IC) at 1 wk of age. The immunization was repeated in the UI group at 2 wk of age. Uninfected (UC) birds served as controls. All animals in UI, IC, and UC groups were challenged orally with 8 x 105 C. baileyi oocysts at the age of 4 wk. Blood samples were collected when birds were 4 and 6 wk of age, and sera were examined by enzyme-linked immunosorbent assay for the presence of antibodies against C. baileyi. Total oocyst output of UI chickens was about 60% of that of UC birds after challenge, and the prepatent and patent periods were nearly identical in the latter 2 groups. In contrast, IC birds developed complete resistance to challenge infections. These results suggest that immunization with the oocyst extract of C. baileyi may confer some degree of protection against oral challenge; however, the protection is less effective than that induced by primary oral infection. The lack of significant difference between the antibody responses of IC and UI animals to C. baileyi at 4 wk of age suggests that serum antibodies play little role in acquired resistance to challenge infection.
ASJC Scopus subject areas
- Ecology, Evolution, Behavior and Systematics