Efficacy of permethrin/imidacloprid (Advantix®) in preventing Leishmania infantum transmission in naturally exposed dogs in Greece

Background Canine leishmaniosis (CanL) by Leishmania infantum is a potentially fatal sand fly-borne zoonosis. Transmission can be reduced by regular use of repellent insecticides. This 12-month study, conducted in a highly endemic CanL area, assessed the efficacy of a repeated spot-on application of imidacloprid 10%/permethrin 50% (Advantix ® , Elanco) to prevent L. infantum transmission in dogs naturally challenged by sand flies versus a negative control. Methods Forty purpose-bred Beagle dogs were allocated to two groups. Group 1 was treated four-weekly with Advantix ® , while group 2 was left untreated. This study was performed in an open-air kennel, consisting of two phases: Phase 1 (Day 0–224; April–November [sand fly season]) allowed natural Leishmania transmission; Phase 2 (Day 225–341; November–March [post sand fly season with insect-proof environment and licensed preventative treatment]) enabled time for seroconversion and disease development. Clinical examinations plus scoring, SNAP serology, and PCR (conjunctival swabs) were performed four-weekly. IFAT, haematology, blood biochemistry, and urinalysis were performed at study start and end. Bone marrow PCR was performed at study end. Sand fly activity was recorded every four weeks by trapping. Sand flies were morphologically identified and screened by PCR for L. infantum infection. Results Advantix ® treatment four-weekly over a whole sand fly season in a highly endemic region resulted in 100% reduction of L. infantum transmission. The incidence in treated dogs was significantly lower than in control dogs (P = 0.003). Treated dogs remained clinically healthy and sero- and PCR-negative, and showed no haematological/biochemical deviations indicative of infection. Untreated dogs became positive for L. infantum from Day 196 onwards: 8/20 dogs (40%) developed positive SNAP, IFAT, and conjunctival and bone marrow PCR. Clinical signs of leishmaniosis and abnormal blood and urine parameters were also observed in these dogs. In total, 1,948 sand flies (1,278 females, 670 males) were collected. 2/7 sand fly batches were PCR-positive for L. infantum . Conclusions In the reported study, four-weekly application of Advantix ® throughout the sand fly season was highly efficacious (100%) in preventing L. infantum transmission to dogs by infected sand flies under natural conditions. Forty per cent of control dogs became positive in diverse test systems and showed signs of leishmaniosis.