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- Author or Editor: Joel V. Walker x
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Abstract
Objective—To determine the virulence of a Brucella abortus mutant, BA25, lacking a major 25 kd outer membrane protein ( Omp25) in cattle.
Animals—20 mixed-breed heifers in late gestation.
Procedure—10 heifers were inoculated with 1 × 107 colony-forming units of the Omp25 mutant via the conjunctival sac, and an equal number were infected with the virulent parental strain B abortus 2308. The delivery status of the dams was recorded, and colonization was assessed following necropsy. The ability of BA25 to replicate inside bovine phagocytes and chorionic trophoblasts was also evaluated in vitro because of the propensity of virulent brucellae to replicate inside these cells in vivo.
Results—The parental strain induced abortions in 5 of 10 inoculated cattle, whereas only 1 of 10 dams exposed to BA25 aborted. Brucella abortus strain 2308 colonized all of the cow-calf pairs and induced Brucella-specific antibodies in 100% of the dams. In contrast, BA25 was isolated by bacteriologic cultural technique from 30% of the calves and 50% of the inoculated dams (n = 10). Of the 10 heifers inoculated with BA25, 4 did not develop Brucella-specific antibodies nor were they colonized by the mutant strain. In bovine macrophages and chorionic trophoblasts, BA25 replicated in significantly lower numbers than the virulent parental strain (n = 3).
Conclusions and Clinical Relevance—The 25 kd outer membrane protein may be an important virulence factor for B abortus in cattle. The attenuation of the Omp25 mutant in cattle may involve the inability of BA25 to replicate efficiently in bovine phagocytes and chorionic trophoblasts.(Am J Vet Res 2001;62:1461–1466)
Abstract
Objective—To develop a novel oral vaccine delivery system for swine, using the rough vaccine strain of Brucella abortus.
Animals—56 crossbred pigs from a brucellosis-free facility.
Procedure—In 3 separate experiments, pigs were orally vaccinated with doses of 1 × 109 to > 1 × 1011 CFU of strain RB51 vaccine. The vaccine was placed directly on the normal corn ration, placed inside a whole pecan, or mixed with cracked pecans and corn.
Results—Oral vaccination of pigs with vaccine strain RB51 resulted in a humoral immune response to strain RB51 and short-term colonization of the regional lymph nodes.
Conclusions and Clinical Relevance—A viscous liquid such as Karo corn syrup in association with pecans that scarify the oral mucosa are necessary when placing the live vaccine directly onto corn or other food rations. Doses of > 1 × 1011 CFU of RB51 organisms/pig in this mixture ensures 100% colonization of regional lymph nodes via the oral route. This method may allow an efficient and economical means to vaccinate feral swine for brucellosis. (Am J Vet Res 2001;62:1328–1331)
