Targeting the tick protective antigen subolesin reduces vector infestations and pathogen infection by Anaplasma marginale and Babesia bigemina

The ultimate goal of vector vaccines is the control of vector infestations while reducing pathogen infection and transmission to protect against the many diseases caused by vector-borne pathogens. Previously (Vaccine 2011;29:2248-2254), we demonstrated that subolesin vaccination and release of tick larvae after subolesin knockdown by RNA interference (RNAi) were effective for the control of cattle tick, Rhipicephalus (Boophilus) microplus infestations in cattle. In this study, we used the fact that these animals were naturally infected with Anaplasma marginale and Babesia bigemina to evaluate the effect of subolesin vaccination and gene knockdown on tick infection by these cattle tick-transmitted pathogens. Ticks fed on vaccinated cattle had lower subolesin mRNA levels when compared to controls, resembling RNAi results. A. marginale and B. bigemina infection was determined by PCR and decreased by 98% and 99%, respectively in ticks fed on vaccinated cattle and by 97% and 99%, respectively after subolesin knockdown. These results demonstrated that targeting subolesin expression by vaccination or RNAi results in lower subolesin mRNA and pathogen infection levels, probably due to the effect of subolesin downregulation on tick feeding, gene expression and gut and salivary glands tissue development and function. These results suggested that subolesin vaccines could be used for the dual control of tick infestations and pathogen infection, a result that could be relevant for other vectors and vector-borne pathogens.