Genetic resistance to Brucella abortus in the water buffalo (Bubalus bubalis)

Brucellosis is a costly disease of water buffaloes (Bubalus bubalis). Latent infections and prolonged incubation of the pathogen limit the efficacy of programs based on the eradication of infected animals. We exploited genetic selection for disease resistance as an approach to the control of water buffalo brucellosis. We tested 231 water buffalo cows for the presence of anti-Brucella abortus antibodies (by the agglutination and complement fixation tests) and the Nramp1 genotype (by PCR-denaturing gradient gel electrophoresis). When the 231 animals (58 cases and 173 controls) were divided into infected (seropositive) and noninfected (seronegative) groups and the Nramp1 genotypes were compared, the seropositive subjects were 52 out of 167 (31%) in the Nramp1A+ (Nramp1AA or Nramp1AB) group and 6 out of 64 (9.4%) in the Nramp1A- (Nramp1BB) group (odds ratio, 4.37; 95% confidence limits, 1.87 to 10.19; chi2, 11.65 for 1 degree of freedom). Monocytes from Nramp1BB subjects displayed significantly (P < 0.01) higher levels of Nramp1 mRNA than Nramp1AA subjects and also a significantly (P < 0.01) higher ability in controlling the intracellular replication of several Brucella species in vitro. Thus, selection for the Nramp1BB genotype can become a valuable tool for the control of water buffalo brucellosis in the areas where the disease is endemic.