VACCINATION OF MICE WITH NEOSPORA-CANINUM - RESPONSE TO ORAL CHALLENGE WITH TOXOPLASMA-GONDII OOCYSTS

Neospora caninum is a protozoan parasite that can cause severe disease in mammals. Two experiments were conducted to examine the effects of subcutaneous (s.c.) vaccination with Hank's balanced salt solution (HB SS), 1 x 10(5) N. caninum NC-1 strain tachyzoites or 1 x 10(5) Toxopla sma gondii TS-4 strain tachyzoites on challenge oral infections in mic e with sporulated VEG strain T. gondii oocysts (1 x 10(3) oocysts exp. 1 and 5 x 10(3) oocysts exp. 2). An additional study, experiment 3, e valuated s.c. challenge with 2.5 x 10(3) tachyzoites of the highly vir ulent RH strain of T. gondii after vaccination with HBSS, NC-1 tachyzo ites, or TS-4 tachyzoites. Mice vaccinated with NC-1 strain tachyzoite s survived significantly (P < 0.05) longer than mice given HBSS in exp eriment 1, but not in experiments 2 and 3. Mice vaccinated with TS-4 s train tachyzoites survived significantly longer than HBSS-vaccinated m ice in experiments 1, 2, and 3 and significantly longer than mice vacc inated with the NC-1 strain in experiments 2 and 3. Toxoplasma gondii tissue cyst numbers were significantly lower for mice vaccinated with TS-4 strain tachyzoites than mice vaccinated with HBSS or the NC-1 str ain tachyzoites in experiment 1. No difference was observed in tissue cyst numbers in mice vaccinated with HBSS or NC-1 strain tachyzoites i n experiment 1. No HBSS-vaccinated mice survived experiment 2, and the numbers of T. gondii tissue cysts were significantly lower for mice v accinated with the TS-4 strain tachyzoites compared to NC-1 strain tac hyzoites. No HBSS- or NC-1-vaccinated mice survived RH strain challeng e in experiment 3. Results of these experiments indicate that infectio n with N. caninum provides some protection against fatal oral infectio n with T. gondii oocysts of a moderately pathogenic strain but not tac hyzoites of a highly pathogenic strain. The protection provided bq N. caninum is much less than that provided by previous exposure to T. gon dii, and the numbers of tissue cysts in the brains of mice are not sig nificantly (P > 00.5) lowered.