Serological Response in Cross-Bred Heifers Immunized With Brucella Abortus Strain Rb51 Vaccine Under Smallholder Dairy Farm Management System in Bangladesh

Abstract

Background: Brucella abortus live vaccines (strains 19 and RB51) have successfully been used to control bovine brucellosis especially to protect cattle against infection and abortion worldwide. Most of the knowledge of the protective immune response of these vaccines against brucellosis induced by immunization derives from the studies in mice. Some studies on humoral immune response of these vaccines have been studied in bovine and buffaloes and an attempt is made further to evaluate the serological responses of RB51 vaccine in cross-bred heifers of smallholder dairy farms in Bangladesh. Objective: This study was conducted to measure serological responses induced in cross-bred dairy heifers immunized with RB51 Brucella abortus vaccine by using indirect ELISA. Materials and Methods: Five cross-bred (Holstein  Local) heifers were selected for this experiment which aged four months and sero-negative for Brucella infection in smallholder dairy farms in the district of Kushtia. Each of the selected heifer received 2.0 ml imported commercial B. abortus RB51 strain vaccine subcutaneously in the neck region at day 0 and then booster dose at 60 days after the first vaccination with similar dose and route during the period from January to July 2020. Each of the collected serum samples of five heifers at day 0, 7, 14, 21, 28, 60, 90, 120 and 150 was tested to detect the antibody status by using commercial indirect ELISA kit. Results: The serological responses (antibody level) was detected by commercial indirect ELISA OD values in the serum of cross-bred heifers induced by using B. abortus strain RB51 commercial live vaccine resulted 0.097 OD value at 0 day (pre-vaccination) and 0.108 at 7th day of post-immunization. It appears that the OD values in the immunized heifers was started to rise from the first week and it was gradually increased and reached the peak level at 60 days (OD value 0.223). Booster vaccination administered at 60 days was resulted peak antibody level at day 90 (OD value 0.313) but its level was started to decline from 120 days with a highest declined at day 150 (OD value 0.199). Conclusions: Further studies to define the cellular immune response and protection against B. abortus infection are recommended before routine use of the vaccine in cattle in Bangladesh.