EVALUACIóN DE LA CEPA S19 Brucella abortus EN EL CONTROL DE LA BRUCELOSIS BOVINA EN ACTOPAN, VERACRUZ, MéXICO

for evaluating the efficacy of brucella abortus s19 strain in bovine herds with a low brucellosis prevalence, 162 females were randomly selected from three herds with similar management conditions and feeding in actopan, ver. and then divided into two groups of 81 each. the first group was vaccinated with 2 ml of s19 brucella abortus strain suspension with 3 x 108 to 3 x 109 colony forming units (cfu) dose for females older than six months including pregnant and those between three and six months with 5 x 1010 cfu. the other one was used as unvaccinated control group. all selected animals were blooded every three months for 18 months. collected serum was processed by card test (ct) as screening assay and reactors were confirmed by rivanol test (riv) in agreement with nom 041 zoo 1995. results were analyzed by chi square (xi2) and relative risk (rr). initial prevalence was 0% for both groups. at first sampling after vaccination, riv identified five positive animals from the vaccinated group for 3.3% prevalence; nevertheless, serum conversion decreased to 2% for the next sampling. thus, two females from the vaccinated group remained as positives during the remaining samplings, so final prevalence was 2%. the control group kept 0% prevalence during all study. it was concluded that to vaccinate low prevalence herds with brucella abortus strain s19 is not useful due to serum conversion inducing antibodies than could remain over 18 months, thus interfering with official diagnosis procedures for brucellosis.