Immune response in Holstein-zebu cross and zebu calves vaccinated with bacillus Calmette-Guérin (BCG) at Bako Agricultural Research Centre, western Ethiopia

Background: Mycobacterium bovis (M. bovis) bacillus Calmette-Gue ́rin (BCG) currently remains the only licensed vaccine for the prevention of tuberculosis. The purpose of this study was to evaluate immune responses in calves vaccinated with BCG in western Ethiopia. Methods: Twelve Holstein-zebus cross breed calves (six vaccinated with 0.5ml of 1 x 106 CFU of BCG and six controls) and nine pure zebu calves (five vaccinated with 0.5ml of 1 x 106 CFU of BCG and four controls) were used in this study. Immune responses were monitored for 23 weeks post vaccination using gamma interferon (IFN-γ) assay and comparative intra-dermal tuberculin test to assess cellular response, and enzyme-liked immunosorbant assay (ELISA) to measure antibody response. Results and interpretation: IFN-γ response was observed starting from week 2, attaining its peak at week 4 post vaccination after which a fall in the response of IFN-γ was observed attaining a constant concentration from week 8 onwards. The mean IFN-γ response (OD450nm: Mean ± SEM, 0.205 ± 0.018) in vaccinated calves was significantly (tcal=2.85, P<0.05) higher than the non-vaccinated calves (Mean ± SEM, 0.168±0.008) at 4th week post vaccination. Within the vaccinated group, the mean IFN-γ response was significantly (tcal=3.01, P<0.05) greater in cross breed (Mean ± SEM, 0.217 ± 0.021) than in zebu breeds (Mean ± SEM, 0.194 ± 0.015) at 4th week post vaccination. On the other hand, no detectable antibody response was observed in vaccinated and non-vaccinated calves while the mean of skin thickness following skin test was significantly (P<0.05) higher in vaccinated calves than in non-vaccinated calves 23 weeks post vaccination. Conclusion: BCG induced IFN-γ responses in both Holstein-zebu cross and zebu calves although stronger IFN-γ response was observed in Holstein-zebu cross breed as compared to the response in zebu, which could suggest the possibility of using BCG for the control of bovine tuberculosis in Ethiopia.