Vaccination with recombinant Boophilus annulatus Bm86 ortholog protein, Ba86, protects cattle against B. annulatus and B. microplus infestations

Abstract

Background: The cattle ticks, Boophilus spp., affect cattle production in tropical and subtropical regions of the world. Tick vaccines constitute a cost-effective and environmentally friendly alternative to tick control. The recombinant B. microplus Bm86 protective antigen has been shown to protect cattle against tick infestations. Recently, the gene coding for B. annulatus Bm86 ortholog, Ba86, was cloned and the recombinant protein was secreted and purified from the yeast Pichia pastoris.

Results: Recombinant Ba86 (Israel strain) was used to immunize cattle to test its efficacy for the control of B. annulatus (Mercedes, Texas, USA strain) and B. microplus (Susceptible, Mexico strain) infestations. Bm86 (Gavac and Mozambique strain) and adjuvant/saline were used as positive and negative controls, respectively. Vaccination with Ba86 reduced tick infestations (71% and 40%), weight (8% and 15%), oviposition (22% and 5%) and egg fertility (25% and 50%) for B. annulatus and B. microplus, respectively. The efficacy of both Ba86 and Bm86 was higher for B. annulatus than for B. microplus. The efficacy of Ba86 was higher for B. annulatus (83.0%) than for B. microplus (71.5%). The efficacy of Bm86 (Gavac; 85.2%) but not Bm86 (Mozambique strain; 70.4%) was higher than that of Ba86 (71.5%) on B. microplus. However, the efficacy of Bm86 (both Gavac and Mozambique strain; 99.6%) was higher than that of Ba86 (83.0%) on B. annulatus.

Conclusion: These experiments showed the efficacy of recombinant Ba86 for the control of B. annulatus and B. microplus infestations in cattle and suggested that physiological differences between B. microplus and B. annulatus and those encoded in the sequence of Bm86 orthologs may be responsible for the differences in susceptibility of these tick species to Bm86 vaccines.

Figure 1

Antibody response in vaccinated cattle. Bovine serum antibody titers to recombinant Ba86 (Israeli strain) and Bm86 (Mozambique strain) antigens were determined by ELISA in cattle vaccinated with Bm86 (Gavac, Cuban Camcord strain), Bm86 (Mozambique strain), Ba86 (Israeli strain) and adjuvant/saline control. Antibody titers in immunized cattle were expressed as the OD_{450 nm} value for the highest serum dilution (1:1000) and compared between vaccinated and control cattle using an ANOVA test (*P < 0.05). The time of vaccination shots (arrows) and tick infestation are indicated.

Figure 2

Sequence comparison of recombinant Bm86 and Bm86 antigens. The protein sequences of the Bm86 (Cuban Camcord in Gavac), Bm86 (Mozambique), Bm86 (Susceptible, Mexico), Ba86 (Israeli strain) and Ba86 (Mission, TX) strains were aligned and the antigenic peptides (≥ 7 residues) predicted using the method of Kolaskar and Tongaonkar [29], with a reported accuracy of about 75% . The predicted antigenic peptides are underlined. The antigenic peptide present in Bm86 but absent in Ba86 (Israel strain) is shown in underlined red letters. The antigenic peptides absent in the Bm86 (Mozambique strain) sequence are shown in underlined blue letters.