Selection of novel tick antigens using vaccination-challenge studies in cattle

Summary

The cost of the cattle tick (Rhipicephalus microplus), to the northern Australian beef industry is presently $170-200M per annum. Currently acaricides (chemicals) are used for the control of the cattle tick.  Due to increasing acaricide resistance and with no new class of acaricide available, a new vaccine to control the cattle tick has been identified as a high priority for the beef cattle industry.  A tick vaccine is considered to be a desirable option for beef producers and would also be commercially appealing to a veterinary pharmaceutical company.  
Through Beef CRC and Queensland Government funding commencing in 2005 and 2007 respectively, all available tick sequences (~14,000) were analysed in silico for predictive antigenic properties. Following immune screening and in vitro tick studies we identified approximately 25 tick vaccine candidates from a pool of over 200.  Ten vaccine candidates with different attributes were chosen for recombinant yeast production for testing in cattle to determine their protective efficacy against cattle tick challenge.  Of these ten vaccine candidates, 6 represented polypeptide constructs (representing 6-10 antigens each construct) and 4 were single antigens. Two of the four singletons were members of different tick multi-gene families and two were novel unknown tick sequences (no predicted function). One polypeptide construct and one unknown singleton showed moderate levels of protective efficacy whilst the remainder were not protective.  The protocols established in this study for both antigen production and cattle tick challenge trials will be used to determine the efficacy of more tick vaccine candidates.  The Beef CRC has commenced discussions with commercial companies.