Bm86 midgut protein sequence variation in South Texas cattle fever ticks

Jeanne M Freeman,Pia U Olafson,Lowell S Kappmeyer,Diane M Kammlah,Ronald B Davey

doi:10.1186/1756-3305-3-101

Jeanne M Freeman, Pia U Olafson + Show 3 more

Open Access

https://doi.org/10.1186/1756-3305-3-101

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Abstract

BackgroundCattle fever ticks, Rhipicephalus (Boophilus) microplus and R. (B.) annulatus, vector bovine and equine babesiosis, and have significantly expanded beyond the permanent quarantine zone established in South Texas. Currently, there are no vaccines approved for use within the United States for controlling these vectors. Vaccines developed in Australia and Cuba based on the midgut antigen Bm86 have variable efficacy against cattle fever ticks. A possible explanation for this variation in vaccine efficacy is amino acid sequence divergence between the recombinant Bm86 vaccine component and native Bm86 expressed in ticks from different geographical regions of the world.ResultsThere was 91.8% amino acid sequence identity in Bm86 among R. microplus and R. annulatus sequenced from South Texas infestations. When South Texas isolates were compared to the Australian Yeerongpilly and Cuban Camcord vaccine strains, there was 89.8% and 90.0% identity, respectively. Most of the sequence divergence was focused in one region of the protein, amino acids 206-298. Hydrophilicity profiles revealed that two short regions of Bm86 (amino acids 206-210 and 560-570) appear to be more hydrophilic in South Texas isolates compared to vaccine strains. Only one amino acid difference was found between South Texas and vaccine strains within two previously described B-cell epitopes. A total of 4 amino acid differences were observed within three peptides previously shown to induce protective immune responses in cattle.ConclusionsSequence differences between South Texas isolates and Yeerongpilly and Camcord strains are spread throughout the entire Bm86 sequence, suggesting that geographic variation does exist. Differences within previously described B-cell epitopes between South Texas isolates and vaccine strains are minimal; however, short regions of hydrophilic amino acids found unique to South Texas isolates suggest that additional unique surface exposed peptides could be targeted.

Highlights

Cattle fever ticks, Rhipicephalus (Boophilus) microplus and R. (B.) annulatus, vector bovine and equine babesiosis, and have significantly expanded beyond the permanent quarantine zone established in South Texas
Based on a calculation of mutation fixation index applied to a sequence fragment containing amino acids 539-573 of Bm86 from Australian, Mexican, Cuban, Venezuelan, and Argentine strains, Garcia-Garcia et al [9] suggested there was an inverse correlation between the vaccine efficacy and sequence variation within the Bm86 locus
The objective of this research was to identify the presence or absence of Bm86 sequence variation found in larval progeny of R. microplus and R. annulatus obtained from cattle and white-tailed deer hosts within the permanent and blanket quarantine zones, as well as outbreak strains established in colony over several generations

Summary

Introduction

Rhipicephalus (Boophilus) microplus and R. (B.) annulatus, vector bovine and equine babesiosis, and have significantly expanded beyond the permanent quarantine zone established in South Texas. Vaccines against cattle fever ticks, the one host ticks that transmit bovine and equine babesiosis, are utilized in endemic countries such as Australia and Cuba [1]. These vaccines are not approved for use in the United States, and current eradication methods established by the United States Cattle Fever Tick Eradication Program rely on acaricide treatment of infested cattle and equids [2]. Available vaccines against cattle fever ticks that are approved for use outside of the United States, including Gavac® (Heber Biotec; Havana, Cuba), TickGARD (Hoechst Animal Health; Australia), and TickGARDPLUS (Intervet Australia; Australia), are based on the recombinant form of the concealed midgut antigen, Bm86. Other possible explanations for variation in vaccine efficacy related to the vector itself include differences in expression levels during targeted tick stages, existence of conformational epitopes not covered by antigen presentation in vaccine preparations, or differences in the quantity of blood and anti-Bm86 antibody imbibed by various tick species [10]

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