Submitted to: Keystone Symposia
Publication Type: Proceedings
Publication Acceptance Date: 1/20/2010
Publication Date: N/A
Technical Abstract: The prevalence of Rhipicephalus (Boophilus) microplus and Rhipicephalus (Boophilus) annulatus cattle infestations have significantly expanded beyond the original quarantine zone established in south Texas as part of the Cattle Fever Tick Eradication Program. Major obstacles for containment of ticks include developing acaracide resistance, transport by wildlife hosts, and lack of an approved and effective vaccine. Vaccines approved for use outside of the United States are based on the recombinant form of the hidden gut antigen, Bm86. The efficacy of these vaccines against tick infestation is highly variable. Sequence variation in Bm86 is a possible but debated explanation for differences in vaccine efficacy. In order to evaluate variation among tick isolates from south Texas, total RNA was isolated from field collected and laboratory colonized tick samples and cDNA was synthesized and sequenced. An amino acid alignment of sequenced isolates revealed 77% sequence identity in the full length Bm86 sequence among all isolates sequenced. There were four main regions where sequence divergence between R. annulatus and R. microplus occurred. Comparisons with vaccine strain sequences revealed several amino acid changes that vary in position among south Texas strains. In vivo immunogenicity trials are necessary to determine whether these changes affect critical protective epitopes in Bm86.