Partial sequencing of Bm86 gene for studying the phylogeny of an Indian isolate of Rhipicephalus (Boophilus) microplus tick

Analysis of Genetic Diversity in Indian Isolates of Rhipicephalus microplus Based on Bm86 Gene Sequence

The control of cattle tick, Rhipicephalus microplus, is focused on repeated use of acaricides. However, due to growing acaricide resistance and residues problem, immunization of animals along with limited use of effective acaricides is considered a suitable option for the control of tick infestations. To date, more than fifty vaccine candidates have been identified and tested worldwide, but two vaccines were developed using the extensively studied candidate, Bm86. The main reason for limited vaccine commercialization in other countries is genetic diversity in the Bm86 gene leading to considerable variation in vaccine efficacy. India, with 193.46 million cattle population distributed in 28 states and 9 union territories, is suffering from multiple tick infestation dominated by R. microplus. As R. microplus has developed multi-acaricide resistance, an efficacious vaccine may provide a sustainable intervention for tick control. Preliminary experiments revealed that the presently available commercial vaccine based on the BM86 gene is not efficacious against Indian strain. In concert with the principle of reverse vaccinology, genetic polymorphism of the Bm86 gene within Indian isolates of R. microplus was studied. A 578 bp conserved nucleotide sequences of Bm86 from 65 R. microplus isolates collected from 9 Indian states was sequenced and revealed 95.6-99.8% and 93.2-99.5% identity in nucleotides and amino acids sequences, respectively. The identities of nucleotides and deduced amino acids were 94.7-99.8% and 91.8-99.5%, respectively, between full-length sequence (orf) of the Bm86 gene of IVRI-I strain and published sequences of vaccine strains. Six nucleotides deletion were observed in Indian Bm86 sequences. Four B-cell epitopes (D519-K554, H563-Q587, C598-T606, T609-K623), which are present in the conserved region of the IVRI-I Bm86 sequence, were selected. The results confirm that the use of available commercial Bm86 vaccines is not a suitable option against Indian isolates of R. microplus. A country-specific multi-epitope Bm86 vaccine consisting of four specific B-cell epitopes along with candidate molecules, subolesin and tropomyosin in chimeric/co-immunization format may provide a sustainable option for implementation in an integrated tick management system.

Genetic diversity of the ATAQ gene in Rhipicephalus microplus collected in Mexico and implications as anti-tick vaccine

The cattle tick Rhipicephalus microplus has a large impact on cattle production due to its bloodsucking habit and transmission of pathogens that cause babesiosis and anaplasmosis. Application of acaricides constitutes the major control method but is often accompanied by serious drawbacks, including environmental contamination and an increase in acaricide resistance by ticks. The recent development of anti-tick vaccines has provided positive results in the post-genomic era, owing to the rise of reverse vaccinological and bioinformatics approaches to analyze and identify candidate protective antigens for use against ticks. The ATAQ protein is considered a novel antigen for the control of the cattle tick R. microplus; it is expressed in midguts and Malpighian tubules of all ticks from the Rhipicephalus genus. However, genetic diversity studies are required. Here, the ATAQ gene was sequenced of seven R. microplus tick isolates from different regions in Mexico to understand the genetic diversity. The results showed that sequence identity among the Mexican isolates ranged between 98 and 100% and 97.8-100% at the nucleotide and protein levels, respectively. Alignments of deduced amino acid sequences from different R. microplus ATAQ isolates in Mexico revealed a high degree of conservation. However, the Mexican isolates differed from the R. microplus "Mozambique" strain, at 20 amino acid residues. Finally, the analysis of more R. microplus isolates, and possibly of other Rhipicephalus species, to determine the genetic diversity in the ATAQ locus is essential to suggest this antigen as a vaccine candidate that might control tick infestations.