Fluralaner activity against life stages of ticks using Rhipicephalus sanguineus and Ornithodoros moubata IN in vitro contact and feeding assays

BACKGROUND: Fluralaner is a novel isoxazoline eliciting both acaricidal and insecticidal activity through potent blockage of GABA- and glutamate-gated chloride channels. The aim of the study was to investigate the susceptibility of juvenile stages of common tick species exposed to fluralaner through either contact (Rhipicephalus sanguineus) or contact and feeding routes (Ornithodoros moubata). METHODS: Fluralaner acaricidal activity through both contact and feeding exposure was measured in vitro using two separate testing protocols. Acaricidal contact activity against Rhipicephalus sanguineus life stages was assessed using three minute immersion in fluralaner concentrations between 50 and 0.05 μg/mL (larvae) or between 1000 and 0.2 μg/mL (nymphs and adults). Contact and feeding activity against Ornithodoros moubata nymphs was assessed using fluralaner concentrations between 1000 to 10⁻⁴μg/mL (contact test) and 0.1 to 10⁻¹⁰μg/mL (feeding test). Activity was assessed 48 hours after exposure and all tests included vehicle and untreated negative control groups. RESULTS: Fluralaner lethal concentrations (LC₅₀, LC₉₀/₉₅) were defined as concentrations with either 50%, 90% or 95% killing effect in the tested sample population. After contact exposure of R. sanguineus life stages lethal concentrations were (μg/mL): larvae - LC₅₀0.7, LC₉₀2.4; nymphs - LC₅₀1.4, LC₉₀2.6; and adults - LC₅₀278, LC₉₀1973. After exposure of O. moubata nymphs to fluralaner lethal concentrations were (μg/mL): contact exposure - LC₅₀720,LC₉₅1133; and feeding exposure- LC₅₀0.00007, LC₉₅0.09. CONCLUSIONS: Fluralaner demonstrates potent in vitro acaricidal activity against all life stages of the brown dog tick, R.sanguineus. The testing of fluralaner contact and feeding routes using O. moubata nymphs demonstrates a high acaricidal activity in both exposure routes.