Reverse vaccinology based identification of anti- Rhipicephalus microplus vaccine candidates

Abstract

The rapid geographic expansion of the cattle tick species, Rhipicephalus microplus, as well as the introduction of diseases into previously unaffected areas and the increased incidence of acaricide resistance in this species are of great concern in Africa and Southern Africa. The feasibility of developing an effective program for tick control that includes vaccination of cattle with tick protective antigens has been demonstrated sufficiently with the Bm86 vaccine. To date, a number of candidates have been identified that have been tested in cattle vaccination trials, but none could infer greater protection compared to Bm86. Genomic approaches to study R. microplus has only recently became possible with the availability of EST and assembled sequences databases (i.e. BmGI database with 13, 643 unique transcripts). During this study, a custom-based oligonucleotide microarray chip was designed from available genomic data allowing the simultaneous transcriptional analysis of some 13,456 R. microplus transcripts. This tool allowed a global view of the transcriptome of various adult female tissues and the immature life stages of R. microplus during feeding on South African cattle breeds. Additional clustering and annotation of transcripts resulted in the identification of biochemical processes and protein families that are unique to or conserved for the different life stages. Consequently global gene expression indicated 85 transcripts as shared between all life stages, along with a number of transcripts that were life stage specific or shared between the life stages tested. A reverse vaccinology approach was followed and the transcriptome data was subjected to bioinformatic and immuno-informatic analysis. Consequently, a set of potential antigens were identified for future evaluation as anti-tick vaccines and the applicability of reverse vaccinology in rational anti-tick vaccine discovery was assessed.