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The brown dog tick, Rhipicephalus sanguineus sensu lato (s.l.) Latreille (Acari: Ixodidae), is a peridomestic, cosmopolitan parasite of dogs known to vector numerous pathogens of veterinary and medical importance. Recent phylogenetic analyses separate this tick into temperate and tropical lineages. Populations of Rh. sanguineus s.l. have been reported to exhibit sodium channel target site insensitivity to permethrin and etofenprox, which is likely due to the prolonged use of pyrethroids against many pests in and around the home. In this study, populations collected in the Caribbean, Africa, Asia, Europe and North America, were tested to identify the distribution of a known resistance mechanism, pathogen-vector interactions and phylogeny in relation to latitude. Using molecular assays, populations from 29 distinct locations were simultaneously geographically typed and screened for bacterial infection by Rickettsia, Ehrlichia, Babesia and Hepatozoon species, and for the presence of a sodium channel single nucleotide polymorphism known to confer permethrin resistance. Implications of these results on Rh. sanguineus s.l. management in association with geographical distribution will be discussed.

The brown dog tick, Rhipicephalus sanguineus (Latrielle) sensu lato, is an important ectoparasite of dogs and occasionally humans, capable of transmitting several pathogens, such as Rickettsia and Ehrlichia, which are of veterinary and medical importance. The brown dog tick is distributed worldwide and has an affinity for human habitations in much of its range. In some populations, lack of integrated pest management plans and overuse of pyrethroid pesticides and other sodium channel inhibitors has resulted in high levels of resistance to permethrin. Recently, a highly conserved region of the R. sanguineus sodium channel was sequenced, indicating that a single nucleotide polymorphism of thymine to cytosine on domain III segment VI of the sodium channel could confer resistance. A molecular assay targeting a point mutation in the sodium channel was developed and optimized to separate ticks expressing permethrin resistance from those from a susceptible colony. Thereafter, multiple field-collected phenotypically permethrin-resistant populations were evaluated using this molecular assay to determine genotype. As confirmed by DNA sequencing, a point mutation was present at a high rate in phenotypically resistant tick populations that was not present in the susceptible strain. These data suggest an additional permethrin resistance mechanism to metabolic resistance, which has been reported for this tick species, and confirm its association with phenotypic resistance. The results of this study further emphasize the need to preserve acaricide chemistry through rotation of active ingredients used to control ectoparasites.

Background The brown dog tick, Rhipicephalus sanguineus sensu lato (Latreille; Acari: Ixodidae), is a peridomestic ectoparasite of dogs and occasionally humans. In some populations, lack of integrated pest management practices and overuse of pesticides has resulted in high levels of resistance to multiple active ingredients. In this study, we established the etofenprox discriminating concentration (DC) and three additional screening concentrations to evaluate resistance status. Using mortality results, cross-resistance was investigated in brown dog tick populations from five geographically disparate regions, including Asia, Africa, Europe, North America, and the Caribbean, following exposure to the DC for both etofenprox and permethrin separately. Subsequently, using both larval packet tests and molecular methods, etofenprox resistance was investigated. Results The etofenprox DC was set at 0.51%, which allows for the rapid screening of peridomestic brown dog tick populations for resistance to this active ingredient. Cross-tolerance to two sodium channel-inhibiting pesticides, permethrin and etofenprox, was observed in one population. Conclusion Our study has provided a single etofenprox concentration that can be used in larval packet tests to determine resistance status in collected peridomestic brown dog ticks, which is particularly important when a single to a few engorged adult ticks are provided for evaluation. Although metabolic resistance is presumed to be the primary resistance mechanism, a sodium channel mutation also confers tolerance to etofenprox at the DC. © 2019 Society of Chemical Industry.