Comparison of humoral immune responses between heat-inactivated Brucella abortus biovar 3 and strain RB51 vaccines in indigenous cattle of Bangladesh

Background: Live attenuated Brucella abortus strains 19 and RB51 vaccines have been used as a key method for the control and eradication of brucellosis in cattle worldwide for decades. Due to certain limitations of these live vaccines, research has been undertaken for the development of an ideal more effective and safer vaccine for animals and human brucellosis. Objective: The main objective of this study was to compare the humoral immune responses (HIR) between the heat-inactivated Brucella abortus biovar 3 and attenuated live RB51 vaccines in native cattle of Bangladesh. Materials and Methods: The methods of isolation, identification, preparation of inoculum dose (10 × 1010 cfu/5 ml) and heat inactivation of B. abortus biovar 3 was followed as described earlier. Each of the three B. abortus sero-negative native cows was inoculated with heat-inactivated B. abortus vaccine @ 5.0 ml (10 × 1010 cfu /5 ml)/ cow SC single injection. Similarly, each of five native calves of 6 to 9 months old was inoculated with live attenuated RB51 vaccine (CZ Veterinaria, SA, Spain) @ 2.0 ml (10-34×109 ) SC as single dose. The sera of cows were collected at 0, 7, 14, 21, 28, 40, 60 and 90 days post vaccination, whereas the sera of the calves were collected at 0, 7, 14, 21, 28, 60, 90, 120, 150 and 180 days post-vaccination. All the collected sera of both the groups were tested to evaluate antibody titer by RBT followed by ELISA with commercial tests kits. Results: The HIR of the cows inoculated with heat-inactivated vaccine showed antibody (Ab) titer started to rise significantly (p < 0.05) from the 14 days (OD 0.2116 ± 0.0397, Ab titer 1:120) and reached a peak level at 28 days (OD 0.319 ± 0.172, Ab titer 1:800) and then started to decline significantly (p < 0.05) from 40 days (OD 0.234 ± 0.0415, Ab titer 1:35) to 60 days (OD 0.094 ± 0.0075, Ab titer 0). The mean Ab titer in calves inoculated with RB51 vaccine showed that Ab titer started to appears insignificantly (p ˃ 0.05) from day 7 (OD 0.094 ± 0.01603) and reached peak level at day 60 days (OD 0.592 ± 0.398), changes are very significant from day 0 (p < 0.05), after 60 days Ab level start to decrease and reach at lowest level at day 150 (OD 0.112 ± 0.0188), Ab level found similar to day 0 (OD 0.0826 ± 0.00517) at 180 days (OD 0.0822 ± 0.00249). Conclusions: The S19 and RB51 are the approved B. abortus vaccine strains have been widely and successfully used with some limitations to prevent bovine brucellosis worldwide. In addition to live attenuated and inactivated vaccines, recombinant genes, proteins, vectors, DNA and recombinant mutant vaccines have also been evaluated for the prevention of brucellosis but further research would be required to develop an ideal vaccine for both the humans and animals.