First report of VGSC mutations for resistance to synthetic pyrethroids in brown dog ticks (Rhipicephalus sanguineus sensu stricto) from Brazil

Background The brown dog tick, Rhipicephalus sanguineus sensu lato (s.l.), is an invasive tick of dogs that has spread globally and is an important vector of multiple pathogens affecting both dogs and humans. It predominately lives in areas where it can easily feed on domestic or stray dogs and commonly takes refuge in and around human dwellings. The control of these ticks often relies on synthetic pyrethroids, a chemical class of acaricides that targets the voltage-gated sodium channel (VGSC) protein of arthropod nerve cells, causing influxes of sodium and ultimately, paralysis. Repeated synthetic pyrethroid treatments against ticks can select for mutations in the VGSC gene that convey resistance to these compounds. Invasive Rhipicephalus sanguineus s.l. ticks in the Americas can be broadly grouped into two main lineages: temperate and tropical ( Rh. sanguineus sensu stricto (s.s.) and Rh. linnaei , respectively). Phenotypic resistance to synthetic pyrethroids in a known Rh. sanguineus s.s. population has only been reported in the state of Rio Grande do Sul, Brazil. In contrast, R. linnaei from the United States and Caribbean islands can display phenotypic resistance based on resistance mutation T2134C in domain III segment 6 of the VGSC gene. Methods We used next-generation DNA sequencing methods to analyze the VGSC gene and mitochondrial loci ( 12S , 16S , COI ) of 10 brown dog ticks sampled from a stray dog in the Restinga sub-district of Porto Alegre, Rio Grande do Sul, Brazil. Ticks from this animal had previously been shown to display low levels of resistance to deltamethrin. Results Analysis of mitochondrial genes confirmed these ticks were Rh. sanguineus s.s. We identified two known resistance mutations in domain II segments 4–5 of the VGSC gene (C190A and G215T). These specific mutations have not been reported previously in any brown dog tick lineages from the Americas, and this is the first case of VGSC mutations described from ticks confirmed to be Rh. sanguineus s.s. using genetic analyses. Conclusions The discovery of these mutations in Rh. sanguineus s.s. is important for the effective management of ticks on dogs in Brazil and other countries where brown dog tick infestations occur.