Antigens of Campylobacter fetus subsp fetus eliciting vaccinal immunity in heifers.

These studies were designed to identify the antigens of Campylobacter fetus subsp fetus that elicit vaccinal immunity. Heifers were vaccinated subcutaneously twice (42 days between vaccinations) with bacterins containing K, O, and H antigens (group A), O and H antigens (group B), or O antigen (group C) of the challenge strain. Five heifers were not vaccinated and served as controls (group D). Two weeks after heifers were given the second vaccination, the immunity of all heifers was challenge exposed by inoculating a live culture against the cervical os. Cervicovaginal mucus samples were examined by microbiological culture technique, using a selective medium, at 7- and 14-day intervals after challenge exposure. One of the six vaccinated heifers in group A became infected, as did all vaccinated heifers in groups B and C and the controls (group D). Only heifers vaccinated with bacterin containing K antigen were resistant to experimental infection with C fetus subsp fetus (P = 0.0002). Humoral antibody responses to whole-cell antigen were monitored, using a tube agglutination test, with and without treatment of the serum with 2-mercaptoethanol. An anamnestic antibody response of 2-mercaptoethanol-resistant antibody was detected in heifers in both groups A and B. An agglutination test (IGGK) was developed to measure immunoglobulin G directed against the K antigen and was used in an attempt to correlate agglutination titers with the immunity to challenge exposure. With the IGGK test, the serum agglutination titers of heifers in group A were significantly higher (P less than 0.0001) than those of heifers in group B. The results of these studies indicate that K antigen of C fetus subsp fetus elicits vaccinal immunity and that a direct correlation exists between the IGGK test and immunity on a group basis.