Identification of cross-protective tick
vaccine antigens is a challenging area of veterinary research. To address this challenge, a recently identified candidate tick protective
antigen, Subolesin (SUB), was targeted in this research. The conservation of subolesin ortholog of Hyalomma anatolicum and Rhipicephalus (Boophilus) microplus across different Indian strains was 98.1-99.4% (within species), while at the
amino acid level SUB sequence homology was ≥53.2% (between tick species). Recombinant R. (B.) microplus SUB (rBmSu) was produced in Escherichia coli and characterized. Cross-bred cattle male calves (N=10) were immunized with three doses of 100 μg each of the rBmSu emulsified in 10%
Montanide 888 at monthly intervals on days 0, 30 and 60. The control group was injected with PBS in 10%
Montanide 888. For the first tick challenge, calves were infested with larvae of R. (B.) microplus generated from 100mg eggs 2 weeks after last immunization (day 75). The immunization resulted in 16.3%, 8.0%, 9.4%, and 26.1% reduction in female tick numbers (DT), weight (DW), oviposition (DO) and egg fertility (DF), respectively, when compared to controls. In the subsequent challenge on day 105, DT, DW, DO and DF were reduced by 9.0%, 4.1%, 8.6%, and 24.2%, respectively, when compared to controls. The
vaccine efficacy (E) was equal to 44.0% and 37.2% after the first and second challenges, respectively. The results showed a positive correlation between antibody titers for both total
IgG and
IgG1 and E in the second but not in the first tick challenge. These results suggested the possibility of developing a SUB-based
vaccine for control of cattle
tick infestations under Indian conditions.