The speed of kill of a topical combination of selamectin plus sarolaner against induced infestations of Ixodes scapularis ticks on cats.

Abstract

The speed of kill of a novel, topical product containing selamectin in combination with sarolaner (selamectin/sarolaner; RevolutionPlus/StrongholdPlus) was evaluated against Ixodes scapularis ticks on cats. Sixteen cats were randomly allocated to a treatment group and treated topically on Day 0 with either placebo (vehicle control) or 6&#x2009;mg/kg selamectin plus 1&#x2009;mg/kg sarolaner. Cats were infested with approximately 50 unfed viable adult I. scapularis ticks on Days -2, 7, 14, 21, 28 and 35. Efficacy was assessed at 4, 8, 12, 24, 48 and 72&#x2009;h after treatment on Day 0 and at 4, 8, 12 and 24&#x2009;h after post-treatment re-infestations. There were no adverse reactions to the topical treatment with selamectin/sarolaner. Placebo-treated cats maintained tick infestations throughout the study. Treatment with selamectin/sarolaner significantly reduced tick counts within 12&#x2009;h (P&#x2009;<&#x2009;0.0001) and resulted in 100% efficacy by 24&#x2009;h. For subsequent re-infestations, live tick counts were significantly reduced by 12&#x2009;h after infestation on Day 7 (P&#x2009;=&#x2009;0.0120) and by 24&#x2009;h for Days 14-35 (P&#x2009;<&#x2009;0.0001). At 24&#x2009;h after the post-treatment re-infestations, efficacy based on geometric (arithmetic) means was &#x2265;96.1% (94.5%) through Day 21, 75.3% (67.7%) on Day 28 and 66.4% (56.4%) on Day 35. Thus, a single topical dose of RevolutionPlus/StrongholdPlus at the recommended minimum dose started killing ticks within 12-24&#x2009;hours after treatment and re-infestations for up to 5 weeks. High acaricidal efficacy (&#x2265;90% reduction in tick burden) was achieved within 24&#x2009;h after treatment and subsequent re-infestations for at least three weeks.