The water buffalo is an important domestic animal worldwide, and the local Buffalypso variety was developed in Trinidad to have improved beef qualities. Brucellosis was diagnosed in Trinidad and Tobago during 1998 in both cattle and domestic water buffalo (Bubalus bubalis) populations. Brucellosis in the latter species is caused by infection with Brucella abortus, similar to bovine brucellosis. Control of brucellosis is of paramount importance to preservation of the genetic diversity of these animals in Trinidad, and this has been complicated by differences in the epidemiology of water buffalo and bovine brucellosis. Some diagnostic tests do not have comparable accuracy between the two species, and the RB51 vaccine does not adequately protect against infection in water buffalo. The water buffalo in Trinidad may also be more resistant to infection than cattle. Development of effective vaccination protocols is key to brucellosis control in Buffalypso in Trinidad, and prohibitions on import of virulent B. abortus strains for vaccine efficacy studies has impeded progress in this area. These Trinidadian strains are of variable virulence; some might be effective for challenge in vaccine efficacy studies, while other, of lower virulence, may be vaccine candidates for use in water buffalo.

Thirty-two water buffalo (Bubalus bubalis) calves aged 6–10 months were used to evaluate serological responses to Brucella abortus strain RB51 (RB51) vaccination in a dose-response study and to compare the use of two selective media for the isolation of RB51. The animals were randomly divided into three treatment groups. Groups I-III received the recommended vaccine dose (RD) twice 4 weeks apart, RD twice 18 weeks apart and saline once, respectively. Lymph nodes were excised from the three groups and subjected to bacteriological examination to determine the frequency of detection of RB51. Pre- and post-vaccination blood samples were collected and tested for B. abortus antibodies using the buffered plate agglutination test (BPAT), complement fixation test (CFT), and dot-blot assay. Sera taken at all post-inoculation weeks (PIW) were negative for field strain B. abortus using the BPAT. Antibody responses to RB51 were demonstrated in all vaccinates but not in controls by CFT and dot-blot assay from 1 PIW up to 16 weeks following booster vaccination. The agreement for both assays was 80.7% and there was a linear interdependence with a Pearson's correlation coefficient value of 0.578. The frequency of isolation of RB51 from the two selective media used was not significantly different (P > 0.05).

The study was conducted to determine the efficacy of Brucella abortus strain RB51 (RB51) vaccine in preventing abortion in pregnant water buffalo (Bubalus bubalis) experimentally challenged using the intravenous route, with a local pathogenic strain of B. abortus biovar 1 (Trinidad 1). Thirty-two female water buffalo calves aged 6-10 months were randomly divided into three groups for the vaccination trial using the subcutaneous route: Group I animals received recommended dose (RD) vaccine twice 4 weeks apart, Group II was vaccinated twice 18 weeks apart and Group III (control) received saline once. At approximately 6 months of pregnancy following natural breeding, the animals were challenged by the intravenous route with 2.5 x 10 8 to 4.4 x 10 8 colony forming units of a local strain of B. abortus, Trinidad 1. Blood samples were collected, pre-challenge and post-challenge, for serological assay using the BPAT and the animals were monitored for clinical signs. The bacteriological study was also performed on tissues of the dams and their calves. The frequency of abortion/stillbirths/early neonatal deaths was 55.6% (5/9), 42.9% (3/7) and 40.0% (2/5) for Groups I, II and III dams respectively (P>0.05; χ 2 ). For calves from infected dams, the frequency of isolation of B. abortus Trinidad 1 from the abomasal and rectal swabs was 100.0%, 80.0% and 100.0% for Groups I, II and III animals respectively (P>0.05). It was concluded that vaccination of water buffalo with the RB51 vaccine using the recommended dose was ineffective in preventing infection, abortion, stillbirths, and neonatal deaths.