Research Information System
ASM Microbe 2019, San Francisco, United States Of America, 20 - 24 June 2019, pp.198
Campylobacter infection is one of the most prevalent causes of infectious ovine abortion in the U.S. and worldwide, with an overall abortion rate of 5-50% (average 23%) in affected flocks. Historically, Campylobacter fetus was the main species associated with ovine abortion, however, our recent work revealed a remarkable shift in the etiology of the disease during the past decades in the U.S. Specifically, our study discovered that a highly virulent C. jejuni clone (named SA) has replaced C. fetus as the predominant cause of ovine abortion outbreaks in the U.S. and clone SA is resistant to tetracycline (the only antibiotic approved for treating sheep abortion in the U.S.). Thus, effective control measures for C. jejuni clone SA are critically needed owing to its importance for animal health. Currently, there are two commercial Campylobacter vaccines available for sheep in the U.S., but their efficacy in protecting against C. jejuni clone SA is unknown. In this study, we performed immunization and challenge studies to evaluate vaccine-induced immunity against clone SA-associated sheep abortion. The two commercial Campylobacter vaccines and an experimental bacterin (made of a clone SA strain IA3902) were administrated subcutaneously into pregnant ewes with two doses at two weeks apart. Two weeks after the second dose, the animals were challenged by intravenous inoculation with ~2×109 CFUs of clone SA strain IA3902. Pre-vaccination and post-vaccination sera were collected to evaluate the antibody responses. Ewes were evaluated for vaginal bleeding and abortion for 21 days post inoculation. Both the two commercial vaccines and the experimental bacterin induced high antibody titers against C. jejuni clone SA, but immunoblotting results showed that the experimental bacterin induced more specific antibodies to clone SA. Notably the experimental bacterin produced 80% protection compared with the sham-vaccinated controls (P < 0.01), whereas the commercial vaccines did not significantly differ from the sham controls in abortion rates. The findings indicate that the homologous bacterin was protective, while the commercial vaccines were ineffective in protecting sheep from C. jejuni clone SA induced abortion. These results strongly suggest that a homologous vaccine is needed to effectively control C. jejuni clone SA on sheep farms