Protection against infection and abortion induced by virulent challenge exposure after oral vaccination of cattle with Brucella abortus strain RB51.

OBJECTIVES: To determine efficacy of orally administered Brucella abortus vaccine strain RB51 against virulent B abortus challenge exposure in cattle as a model for vaccination of wild ungulates. ANIMALS: 20 mixed-breed beef cattle obtained from a brucellosis-free herd. PROCEDURE: Sexually mature, Brucella-negative beef heifers were vaccinated by mixing > 10' viable RB51 organisms or diluent with their feed. Heifers were fed individually and consumed their entire ration. Each heifer received approximately 3 X 10' colony-forming units (CFU). Six weeks after oral vaccination, heifers were pasture-bred to brucellosis-free bulls. At approximately 186 days' gestation, heifers were challenge exposed conjunctively with 107 CFU of virulent B abortus strain 2308. RESULTS: Vaccination with the rough variant of B abortus RB51 did not stimulate antibodies against the O-polysaccharide (OPS) of B abortus. After challenge exposure and parturition, strain 2308 was recovered from 80% of controls and only 20% of vaccinates. Only 30% of the vaccinates delivered dead, premature, or weak calves, whereas 70% of the controls had dead or weak calves. CONCLUSIONS: Cattle vaccinated orally with the rough variant of B abortus strain RB51 develop significant (P < 0.05) protection against abortion and colonization and do not produce OPS-specific antibodies. Clinical Relevance-Results encourage further investigation into use of strain RB51 to vaccinate wild ungulates (elk and bison) orally.

National seroprevalence of Toxoplasma gondii in pigs.

Serum samples from 11,842 commercial pigs killed in 1983-1984 throughout the United States were tested for anti-Toxoplasma gondii antibodies by the agglutination test in dilutions of 1:25, 1:50, and 1:500. Anti-T. gondii antibodies were found in 23.9% of pigs. At dilutions of 1:25, 1:50, and 1:500, 13.5%, 6.9%, and 3.5% were serologically positive, respectively. The prevalence of anti-T. gondii antibodies was higher in breeder pigs (42%) than in market pigs (23%). These results indicate that anti-T. gondii antibodies are widespread in the national swine herd.

Relationship of strain 19 calfhood vaccination in beef herds and brucellosis reactor rates, duration of quarantine, and number of herd tests.

Initial and cumulative reactor rates for strain 19 vaccinates and nonvaccinates were significantly (P less than 0.001) lower for beef herds containing variable proportions of vaccinates, compared with reactor rates in nonvaccinated herds. In addition, significant (P less than 0.005) reduction in cumulative incidence was observed in nonvaccinated and strain 19-vaccinated cattle as the proportion of vaccinates within the herd increased from 1 to 19%, 20 to 39%, 40 to 59%, and 60 to 100%. Duration of quarantine and number of herd tests were not reduced in herds with strain 19-vaccinated cattle. In herds released from quarantine, duration of quarantine and number of tests were positively correlated to proportion of the herd vaccinated. In nonvaccinated herds released from quarantine, effect of herd size was documented by strong positive (P = 0.042) correlation with duration of quarantine and slightly weaker correlation (P = 0.095) with number of tests.