Pregnant Guinea Pig Model for Testing Efficacy of Campylobacter fetus Vaccines

Abstract

SUMMARY Pregnant guinea pigs were used in lieu of pregnant sheep to evaluate the efficacy of Campylobacter fetus bacterins. The 50% end point minimum abortive dose (mad50) was determined for C fetus subspecies jejuni serotype C (Berg) strain 917–958. For vaccine evaluation, the optimum challenge dose was determined by intraperitoneal inoculation of vaccinated guinea pigs with 1 mad50, 10 mad50, and 100 mad50 doses per animal. When the protection afforded by an experimental vaccine was evaluated, 100 mad50 doses appeared to be satisfactory. Experimental vaccine containing C fetus serotype C and Freund's adjuvant protected 100% of the guinea pigs challenge exposed with 1 and 10 mad50 doses and 80% against challenge exposure with 100 mad50 doses. A commercially prepared vaccine containing C fetus serotype C and A protected only 16% against abortion when 100 mad50 doses were used as the challenge. There are advantages in using pregnant guinea pigs as the model for evaluating C fetus vaccines rather than the primary host. Guinea pigs are very susceptible to C fetus infection and can be protected against substantial challenge exposure with a given C fetus serotype. Thus, because of the ease of pregnancy diagnosis after 15 days and the short gestation in the guinea pigs the evaluation of a bacterin can be completed within 60 days; in sheep, evaluation period would be 1 year. However, the association of efficacy between guinea pigs and sheep must still be made.