Laboratory evaluation of the efficacy of lotilaner (Credelio™) against Amblyomma cajennense (sensu lato) infestations of dogs

The ixodid tick Amblyomma cajennense ( sensu lato ) complex, widespread throughout South and Central America, is also present in Mexico, Texas and Florida. As a vector of Rickettsia rickettsii , and potentially of other pathogens, infestations with A. cajennense present a substantial health risk to humans, dogs and other mammals. Oral administration of lotilaner flavored chewable tablets (Credelio TM , Elanco) to dogs was previously shown to rapidly provide killing activity of infesting ticks. This study investigated lotilaner’s efficacy against A. cajennense ( s.l .). Twenty purpose-bred Beagles (10 male and 10 female) were ranked by Day -5 burdens of nymphal A. cajennense ( s.l .) and randomized to either treatment with lotilaner or to a sham-treated control group. On Day 0, dogs were fed within approximately 30 min prior to oral lotilaner administration at as close as possible to 20 mg/kg, the minimum dose rate. For efficacy assessments, tick counts were completed 48 h post-treatment or 48 h after experimental challenge infestations with 200 nymphal A. cajennense ( s.l .) on Days -7, -2, 7, 14, 21 and 28. Tick infestations in the control group dogs ranged from a low of 43 to 95, with the average infestation remaining above 25% at each assessment, thereby meeting the requirement for efficacy comparison with the treated group. Lotilaner efficacy was 100% within 48 h post-treatment, and at nine days post-treatment. Efficacy was greater than 99% at all subsequent assessments through Day 30. No treatment-related adverse events were observed. The results demonstrate that lotilaner, administered orally to dogs at a minimum dose of 20 mg/kg is well tolerated, provides rapid reduction of existing A. cajennense ( s.l .) tick infestations, and provides sustained residual protection for at least 30 days against subsequent infestation by A. cajennense ( s.l .).