Venezuelan field trials of vaccines against brucellosis in swine

OBJECTIVE: To evaluate live attenuated Brucella abortus RB51, killed B suis cells, O-polysaccharide (OPS) from B abortus 1119-3 and OPS from B suis 1330, for protection of swine against B suis challenge exposure under farm conditions. ANIMALS: 10 infected boars, 160 unvaccinated control sows and their 1,040 progeny, and 610 vaccinated sows and their 6,600 progeny. PROCEDURE: Gilts (45 to 65 days or 4 to 6 months old) were vaccinated or not vaccinated. For the latter gilts, additional variables studied were dose, number of doses, and delivery route. Mature gilts were mated with 4 infected boars, then serologic reaction to Brucella spp, results of bacteriologic culture of vaginal secretions, presence of abortion, and litter size were assessed. Various tissues obtained from aborted fetuses were obtained for culture of Brucella spp. RESULTS: About 40% of unvaccinated control gilts seroconverted to Brucella spp, 27% were positive for OPS precipitation by use of agar gel immunodiffusion, 23% aborted their fetuses, and the remaining gilts had litters of 5 to 8 pigs. Killed B suis cells provided the following protection: 25% of vaccinates were seropositive, 5% had positive results of agar gel immunodiffusion, 5% aborted, and the remaining gilts had litters of 7 to 8 pigs. Gilts that received live RB51 or OPS vaccine were protected. Serologic reactions were always negative, abortion did not occur (i.e., 100% were protected), and litter size was 10 to 12 pigs. CONCLUSIONS: Live attenuated B abortus RB51 or purified OPS was effective in protecting gilts against B suis infections. Dose (10(6) to 10(9) cells, 100 to 500 micrograms, respectively), number of doses (1 or 3), or route (IM or PO) made little difference. Further research is required to determine why these 2 vaccine candidates are similar in protection effectiveness and whether they can be used after infection as a treatment.