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 co ntrol 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) we re vaccinated or not vaccinated. For the latter gilts, additional vari ables studied were dose, number of doses, and delivery route. Mature g ilts were mated with 4 infected boars, then serologic reaction to Bruc ella spp, results of bacteriologic culture of vaginal secretions, pres ence of abortion, and litter size were assessed. Various tissues obtai ned from aborted fetuses were obtained for culture of Brucella spp. Re sults-About 40% of unvaccinated control gilts seroconverted to Brucell a spp, 27% were positive for OPS precipitation by use of agar gel immu nodiffusion, 23% aborted their fetuses, and the remaining gilts had li tters of 5 to 8 pigs. Killed B suis cells provided the following prote ction: 25% of vaccinates were seropositive, 5% had positive results of agar gel immunodiffusion, 5% aborted, and the remaining gilts had lit ters of 7 to 8 pigs. Gilts that received live RB51 or OPS vaccine were protected. Serologic reactions were always negative, abortion did not occur (ie, 100% were protected), and litter size was 10 to 12 pigs. C onclusions-Live attenuated B abortus RB51 or purified OPS was effectiv e in protecting gilts against B suis infections. Dose (10(6) to 10(9) cells, 100 to 500 mu g, respectively), number of doses (1 or 3), or ro ute (IM or PO) made little difference. Further research is required to determine why these 2 vaccine candidates are similar in protection ef fectiveness and whether they can be used after infection as a treatmen t.