Treatment of chickens with fluralaner induced mortality in pyrethroid-resistant Triatoma infestans (Hemiptera, Triatominae).

Background: Residual spraying with pyrethroid insecticides is still the main strategy used to prevent vector-borne transmission of Trypanosoma cruzi, the etiological agent of Chagas disease. The emergence of resistance to these insecticides in triatomine populations associated with vector control failure highlights the need to evaluate alternative tools, such as xenointoxication. Chickens serve as important blood meal sources and are positively associated with triatomine abundance. Therefore, several endectocides have been tested in chickens, with fluralaner exhibiting the best results. However, the effect of treating chickens with fluralaner has not been evaluated in pyrethroid-resistant triatomines. Here, we aimed to assess the efficacy and duration of the lethal effect of fluralaner on pyrethroid-resistant and susceptible Triatoma infestans using chickens as treated hosts under semi-experimental conditions with a treated-control design.

Methods: Three chickens received two oral doses of Bravecto^® (fluralaner, MSD Animal Health) at 0.5 mg/kg, whereas three other chickens were assigned to the control group, which received only semolina. Third- to fifth-instar nymphs, both susceptible and resistant to pyrethroid insecticides, were exposed to the chickens at five specific times: 0 (pre-treatment), 3, 7, 14, and 28 days post-treatment (DPT). We recorded the degree of triatomine engorgement and assessed feeding success and survival after each exposure. The data were analyzed via logistic regressions and Kaplan‒Meier curves.

Results: Feeding success rates were high, ranging from 95.5% to 100% throughout the trial, and were not affected by treatment or exposure time. The greatest lethal effects of fluralaner on triatomines exposed to treated chickens were observed up to 14 DPT, with cumulative mortality ranging from 76.9% to 87.0%. At 28 DPT, triatomine mortality decreased significantly to 12.8%, similar to the control group means (< 17.9%) and pre-treatment levels (6.8%). No difference in the lethality of fluralaner was detected between susceptible and pyrethroid-resistant triatomines via logistic regression analysis.

Conclusions: On the basis of these and previous results, chickens are eligible for a field study that addresses the efficacy of simultaneous xenointoxication of various hosts using fluralaner. This approach provides a promising alternative for addressing the challenge of resistance to pyrethroid insecticides in triatomines.