Evaluation of a topical solution containing 65% permethrin against the sandfly (Phlebotomus perniciosus) in dogs

A topical solution containing 65% permethrin (EXspot, Schering-Plough Animal Health Corp., Union, NJ) was evaluated for repellency and insecticidal activity against the phlebotomine sandfly, Phlebotomus perniciosus (Diptera: Psychodidae). Four dogs were sedated and individually exposed to 100 female P. perniciosus inside a cage. Two of the dogs were treated on Day 0 with the permethrin solution by application of a 2-ml dose directly on the skin along the dorsal midline from the dorsal scapular area to the base of the tail. Two dogs remained untreated as controls. On Days -8, 0, 7, 14, 21, 28, 35, 49, 70, and 91, sandfly landings were recorded during the first 5 minutes of an insect exposure period and insect feeding and mortality rates were recorded after 1 hour of exposure. The number of sandfly landings was moderately decreased, and insect feeding rates decreased to zero by Day 7. From Day 14 through Day 28, the number of insect feedings was reduced from control values by greater than 90%. These findings indicate the permethrin spot-on provided a considerable repellent effect. Insect mortality rates remained very high (about 61%) during the 5 weeks after application, although insecticidal effects persisted for more than 7 weeks in total. These data suggest that monthly application of this topical solution of permethrin from the end of spring until the beginning of fall may protect dogs from the majority of sandfly bites. Further investigation with greater numbers of animals is warranted; however, results of this preliminary investigation indicate that a leishmaniasis control program that incorporates the strategic use of this product on dogs can be expected to decrease the number of infected animals and the incidence of the disease among the canine population.