Microfilaricidal efficacy of a single administration of Advocate® (Bayer Animal Health) in dogs naturally infected with Dirofilaria immitis or Dirofilaria repens

The present study evaluated the microfilaricidal efficacy of a single application of the spot-on containing imidacloprid 10%/moxidectin 2.5% (Advocate®, Bayer Animal Health) in dogs naturally infected either by Dirofilaria immitis or Dirofilaria repens. Dogs living in north-eastern and central-southern Italy, endemic for D. immitis and D. repens respectively, were randomly screened. Sixteen animals, eight infected with D. immitis and eight with D. repens, and fulfilling inclusion criteria were enrolled. Dogs infected with D. immitis received an adulticide treatment prior to the study and Advocate® 3 weeks after. The animals were divided in blocks of two (1:1, T1:T2) animals each, where Day 0 (D0) had an interval of 15 days to compare T2 vs. T1 dogs during the first fortnight of examination (i.e. T2 dogs acted as control animals at each examination). At baseline (Days −15 and 0 for T2 and T1 dogs, respectively) the animals had a range of microfilaraemia of 180–99.700 mff/ml (D. immitis) and 60–750 mff/ml (D. repens). All animals received a topical administration of Advocate® at D0 and were examined for microfilariae with microscopic and molecular tests at D15, D30, D60 and D90. All animals scored negative for mff at the first control post-treatment and throughout the study, with the exception of two D. immitis- infected animals that had a 2 mff/ml count at D15, and then become negative from Day 30 onwards. No adverse events were observed. The present study demonstrates the safety and the high microfilaricidal efficacy (99.97% and 100% for D. immitis and D. repens, respectively) of a single dose of moxidectin contained in Advocate® in naturally infected dogs.