Comparative speed of kill of induced Ixodes scapularis infestations following treatment of dogs with endectocides containing either sarolaner (Simparica Trio™), afoxolaner (NexGard® PLUS), or lotilaner (Credelio Quattro™)

BACKGROUND: Ixodes scapularis is a consequential tick species in North America that can transmit multiple pathogens of canine and public health significance. Acaricidal speed is critical for reducing the risk of pathogen transmission. Herein, the immediate and sustained acaricidal speed of three monthly oral endectocide products against I. scapularis are compared. METHODS: Thirty-two dogs were randomly allocated equally among four groups and treated on day 0 with an endectocide containing lotilaner (Credelio Quattro™), afoxolaner (NexGard® PLUS) or sarolaner (Simparica Trio™), or left untreated. On days -2, 21, and 28, dogs were infested with 50 laboratory-reared, adult I. scapularis. Live tick counts were performed at 4, 8, 12, 24, and 48-h post-treatment, and after each reinfestation. Efficacy was compared using a linear mixed model of geometric mean live tick counts. RESULTS: At 8-h post-treatment of an existing infestation, only the lotilaner group had significantly lower mean live tick counts than the untreated group. At each subsequent assessment through 48 h, all treated groups had significantly lower mean live tick counts than the untreated group. Compared to the untreated group, following the day 21 reinfestation, mean live tick counts were significantly lower in the lotilaner group at 4 through 48 h, in the sarolaner group at 4, 24, and 48 h, and in the afoxolaner group at 24 and 48 h. Compared to the untreated group, following the day 28 reinfestation, mean live tick counts were significantly lower in the lotilaner group at 8 through 48 h, in the sarolaner group at 12 through 48 h and, in the afoxolaner group at 24 and 48 h. Within group, between day 0 and day 28, significant slowing of acaricidal speed was observed for sarolaner at the 12-h timepoint and for afoxolaner at the 8, 12, and 24-h timepoints. No significant loss of acaricidal speed occurred for lotilaner between day 0 and day 28. CONCLUSIONS: In dogs, lotilaner has a faster onset of acaricidal activity against I. scapularis than sarolaner or afoxolaner. Lotilaner's acaricidal speed is sustained throughout the monthly dosing interval, whereas sarolaner and afoxolaner show slower acaricidal activity at the end of the month than at the beginning.