Identification of protective antigens by RNA interference for control of the lone star tick, Amblyomma americanum

The lone star tick, Amblyomma americanum, vectors pathogens of emerging diseases of humans and animals in the United States. Currently, measures are not available for effective control of A. americanum infestations. Development of vaccines directed against tick proteins may reduce tick infestations and the transmission of tick-borne pathogens. However, the limiting step in tick vaccine development has been the identification of tick protective antigens. Herein, we report the application of RNA interference (RNAi) for screening an A. americanum cDNA library for discovery of tick protective antigens that reduce tick survival and weights after feeding. Four cDNA clones, encoding for putative threonyl-tRNA synthetase (2C9), 60S ribosomal proteins L13a (2D10) and L13e (2B7), and interphase cytoplasm foci protein 45 (2G7), were selected for vaccine studies in cattle, along with subolesin, a tick protective protein identified previously. In vaccinated cattle, an overall efficacy (E) > 30% was obtained when considering the vaccine effect on both nymphs and adults, but only 2D10, 2G7 and subolesin affected both tick stages. The highest efficacy of control for adult ticks (E > 55%) was obtained in cattle vaccinated with recombinant 2G7 or subolesin. These collective results demonstrated the feasibility of developing vaccines for the control of lone star tick infestations. The use of RNAi for identification of tick protective antigens proved to be a rapid and cost-effective tool for discovery of candidate vaccine antigens, and this approach could likely be applied to other parasites of veterinary and medical importance.