Abstract
The bovine tick Rhipicephalus (Boophilus) microplus is found in several tropical and subtropical regions of the world. This parasite transmits pathogens that cause disease, such as babesiosis (Babesia bovis and B. bigemina) and anaplasmosis (Anaplasma marginale). Tick infestations cause enormous livestock losses, and controlling tick infestations and the transmission of tick-borne diseases remains a challenge for the livestock industry. Because the currently available commercial vaccines offer only partial protection against R. (B.) microplus, there is a need for more efficient vaccines. Several recombinant antigens have been evaluated using different immunization strategies, and they show great promise. This work describes the construction and immunological characterization of a multi-antigen chimera composed of two R. (B.) microplus antigens (RmLTI and BmCG) and one Escherichia coli antigen (B subunit, LTB). The immunogenic regions of each antigen were selected and combined to encode a single polypeptide. The gene was cloned and expressed in E. coli. For all of the experiments, two groups (treated and control) of four Angus heifers (3–6 months old) were used. The inoculation was performed via intramuscular injection with 200 μg of purified recombinant chimeric protein and adjuvated. The chimeric protein was recognized by specific antibodies against each subunit and by sera from cattle inoculated with the chimera. Immunization of RmLTI-BmCG-LTB cattle reduced the number of adult female ticks by 6.29% and vaccination of cattle with the chimeric antigen provided 55.6% efficacy against R. (B.) microplus infestation. The results of this study indicate that the novel chimeric protein is a potential candidate for the future development of a more effective vaccine against R. (B.) microplus.
Highlights
Vaccines containing the recombinant antigen Bm86 isolated from the Rhipicephalus (Boophilus) microplus intestine have been developed and marketed to induce immunological protection against tick infestation in cattle
Data generated by using the recombinant Bm86-Campo Grande antigen (BmCG) allowed the identification and characterization of recombinant antigens with immunogenic potential for use in more effective vaccines [4,5,6]
By comparing the observed optical densities and the pH levels of the Terrific Broth (TB) and 2x (YT) culture media, we found that the TB culture medium achieved the ideal OD for the induction (18 h) in a shorter period of time (OD = 0.6) than the 2x (YT) medium (OD = 0.5); the latter medium had a more stable pH under the same standardization conditions, which was similar to the results from the shakers (Fig 4A and 4B)
Summary
Vaccines containing the recombinant antigen Bm86 isolated from the Rhipicephalus (Boophilus) microplus intestine have been developed and marketed to induce immunological protection against tick infestation in cattle. Tick management through vaccination reduces environmental contamination and prevents the selection of drug-resistant ticks that results from the continuous application of acaricides. Tick vaccines are an attractive method for controlling ticks, but their efficacy needs to be improved. In Brazil, the vaccines TickGardPLUS (Intervet Australia) and GavacTM (Heber Biotec S.A., Cuba) have lower efficiencies than vaccines from other countries (49.2% and 46.4%, respectively) [2]. Vaccine efficiency should be greater than 50%, as observed in studies involving recombinant proteins identified by sialotranscriptome analysis, where the vaccine conferred an efficacy of 73.2% [3]. Data generated by using the recombinant Bm86-Campo Grande antigen (BmCG) allowed the identification and characterization of recombinant antigens with immunogenic potential for use in more effective vaccines [4,5,6]
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