Reduction of tick infections with Anaplasma marginale and A. phagocytophilum by targeting the tick protective antigen subolesin.

Subolesin was recently shown by both gene silencing and immunization with the recombinant protein to protect against tick infestations, and to cause reduced tick survival and degeneration of gut and salivary gland tissues. In this research, we extended these studies by testing whether targeting subolesin by RNAi or vaccination interfered with the ability of ticks to become infected with two tick-borne pathogens, Anaplasma marginale which causes bovine anaplasmosis and Anaplasma phagocytophilum, the causative agent of human granulocytin anaplasmosis. For the A. marginale studies, Dermacentor variabilis males were injected with subolesin dsRNA or saline and then were allowed to feed on cattle with ascending rickettsemias, while for the A. phagocytophilum studies, mice were immunized with the recombinant subolesin protein, infected with the pathogen and then infested with larval Ixodes scapularis. Tick infections were determined by quantitative polymerase chain reaction of gut and salivary gland tissues. In both experimental approaches, tick infections were significantly reduced. These results suggest that subolesin appears to be a candidate vaccine antigen that may contribute to control of multiple tick species and the reduction of tick-borne pathogens.