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.
