Abstract
This study aimed to evaluate the efficacy of imidacloprid 10 %/moxidectin 2.5 % (w/v) spot-on (Advocate®/Advantage® Multi, Bayer) against adult Dirofilaria repens in a blinded, placebo-controlled randomised laboratory study. Twenty-four Beagle dogs were experimentally infected with approximately 75 infective D. repens larvae each on study day (SD) 0. Treatment was initiated on SD 228 after patency had been confirmed in 21 dogs, using a modified Knott Test. Eleven dogs received monthly treatments with imidacloprid/moxidectin at the minimum therapeutic dose (10 mg/kg imidacloprid and 2.5 mg/kg moxidectin) for six consecutive months and 12 control dogs were treated with a placebo formulation. Approximately one month after the last treatment, all dogs were euthanised and necropsied for the detection of D. repens worms. Eleven control dogs harboured live adult D. repens (range 2-11, geometric mean 5.44). Eight of 11 imidacloprid/moxidectin-treated dogs were free of live worms. The live worm count was reduced by 96.2 % (range 0-1, geometric mean 0.21). The majority of dead worms were encapsulated and degenerated. After the first treatment, Knott Tests were negative in all imidacloprid/moxidectin-treated dogs and this status was maintained in 10 dogs until study end. One dog showed a low microfilariae count (1 and 4/mL) on four occasions but was also negative before necropsy. The treatment was well tolerated by all study animals. It is concluded that six consecutive monthly treatments with imidacloprid/moxidectin spot-on are effective and safe against adult D. repens and provide an option for preventing the further spread of this zoonotic parasite.
Highlights
In recent years human dirofilariosis has been considered an emerging zoonosis in Europe (Genchi et al 2011)
This study demonstrated the adulticidal efficacy of six consecutive monthly treatments with imidacloprid/moxidectin spot-on (Advocate®/Advantage multi®, Bayer) against D. repens in experimentally infected dogs
Due to missing data in the literature it was not clear what picture could be expected at necropsy and how adult D. repens killed by an anthelmintic would present
Summary
In recent years human dirofilariosis has been considered an emerging zoonosis in Europe (Genchi et al 2011). Dogs represent the main reservoir, and the only effective way to protect humans from the disease is to control the infection in dogs (Genchi et al 2010) Difficulties in putting this into practice arise from the fact that infected dogs are often asymptomatic and remain undiagnosed, or symptoms that may occur, such as pruritus, dermal swelling, hyperpigmentation or subcutaneous nodules are misinterpreted. Macrocyclic lactones, which are labelled to prevent heartworm disease and are used in higher doses to clear dogs of the microfilariae of Dirofilaria immitis, showed variable results against D. repens. Treatment with doxycycline has been shown to weaken or even kill filarial nematodes by killing their endosymbionts (Wolbachia) It is not yet clear whether there is true synergism or just an additive effect, the combination of doxycycline/ivermectin has a much higher efficacy than ivermectin alone against D. immitis (Kramer and Genchi 2014). The efficacy of selamectin at the recommended dose for heartworm prevention has been de-
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