Spot-on application of fluralaner on cats produces high mortality in pyrethroid-resistant and susceptible Triatoma infestans, in comparison with spinosad and imidacloprid

Abstract

Pyrethroid resistance is an increasing threat to vector control programs worldwide. Triatomines, the vectors of Chagas disease are also exhibiting resistant phenotypes. In the Gran Chaco region the increasing emergence of pyrethroid-resistant Triatoma infestans populations calls for renewed efforts in search of alternative tools that could complement traditional vector control activities based on insecticide spraying. With this intention, we evaluated the efficacy of three commercially available ectoparasiticides for veterinarian use in cats: fluralaner (Bravecto®), imidacloprid (Power Met®) and spinosad (Power®), on the mortality of pyrethroid-resistant and -susceptible T. infestans. The trial included 25 domestic, owned cats, randomly assigned to one of the three treatments or two control groups. Bioassays were performed at 0, 4, 30 and 60 days post-treatment (DPT) and consisted in exposing groups of laboratory-reared third to fifth-instar nymphs to each cat. Kaplan-Meier curves showed a significant reduction of survival probability in the triatomines exposed to cats treated with fluralaner and spinosad comparing with their respective controls whereas no lethal effects were observed in the imidacloprid-treated group. In fluralaner-treated cats, triatomines exhibited 80 %, 54 % and 29 % of mortality at 4, 30 and 60 DPT, respectively; whereas in spinosad-treated cats, triatomines achieved 56 % and 37 % of mortality at 4 and 30 DPT, respectively. No significant effect of triatomines pyrethroid-susceptibility status was observed. Given the higher mortality levels achieved and longer lethal effect, our results support the evaluation of cat treatment with fluralaner in a Phase II trial to cope with current challenges of vector control like pyrethroid-resistance.