Field efficacy of moxidectin in dogs and rabbits naturally infested with Sarcoptes spp., Demodex spp. and Psoroptes spp. mites

Abstract

The efficacy of moxidectin 1% injectable for cattle was evaluated in dogs and rabbits with naturally acquired sarcoptic, demodectic or psoroptic mites. Twenty-two dogs with generalised demodicosis were orally treated with 0.4 mg/kg moxidectin daily. Forty-one dogs suffering from sarcoptic mange were treated with 0.2–0.25 mg/kg moxidectin either orally or subcutaneously every week for three to six times. Seven rabbits were treated orally with 0.2 mg/kg moxidectin twice 10 days apart. Of the 22 dogs with demodicosis, 14% were stopped treatment because of side effects, 14% were lost and of the remaining 72% all were cured (mean therapy duration 2.4 months). Thirty-seven of the sarcoptic mange-infected dogs finished treatment and were cured. In 17% of dogs, side effects were noted. All seven rabbits treated for psoroptic mange were cured and did not show any side effect. Our results indicate that moxidectin is effective and a good alternative for the treatment of demodicosis and scabies in dogs and psoroptic mange in rabbits. Side effects seem to occur more frequently if applied subcutaneously, therefore the oral route should be preferred.

Introduction

The avermectin-class antiparasitic agent — moxidectin, is a macrocyclic lactone, which includes two distinct chemical families: avermectins (ivermectin, abamectin, doramectin, eprinomectin, salinomectin) and milbemycins (moxidectin, milbemycin oxime). Moxidectin is produced by a combination of fermentation and chemical synthesis. Streptomyces cyaneogriseus produces nemadectin, which is chemically modified. Moxidectin is a semi-synthetic methoxime derivative of nemadectin (Plumb, 1999). It does not have ivermectin’s disaccaride side chain at C13, but does have the methoxime at C23 and dimethyl-butenyl side chain at C25 (Hayes, 1994). Each member of the macrocyclic lactones may exert a similar mode of antiparasitic action but there is a variation in the efficacy which is presumed to relate to variations in the chemical structure (Shoop et al., 1995).

The primary mode of action is to affect chloride ion channel activity in the nervous system of nematodes and arthropods. Moxidectin binds to receptors that increase membrane permeability to chloride ions. Thus the electrical activity of nerve cells in nematodes and muscle cells in arthropods is inhibited and the parasites become paralysed and die. In addition the release of gamma amino butyric acid (GABA) is enhanced at pre-synaptic neurons. GABA acts as an inhibitory neurotransmitter and blocks the post-synaptic stimulation of the adjacent neuron in nematodes or the muscle fibre in arthropods (Plumb, 1999).

Moxidectin has a broad spectrum of activity against both internal and external parasites (Shoop et al., 1995). In cattle it is licensed for the treatment of gastrointestinal parasites, lungworms, cattle grubs, mites, lice and hornflies, and in horses and sheep it is licensed for the treatment of gastrointestinal parasites. In dogs moxidectin is a monthly oral formulation for the prevention of heartworms. There are several studies using ivermectin (Paradis and Ristic, 1993; Ristic et al., 1995; Fondati, 1996; Medleau et al., 1996; Paradis, 1999; Mueller et al., 1999; Mueller and Bettenay, 1993) or milbemycin oxime (Garfield and Reedy, 1992; Mueller and Bettenay, 1995; Paradis, 1999) in dogs for the treatment of infestation with Demodex spp. mites, ivermectin against Cheyletiella spp. in cats (Paradis and Scott, 1990), milbemycin oxime as treatment of canine scabies — Sarcoptes spp. (Miller et al., 1996; Shipstone et al., 1997). Several studies show the efficacy of ivermectin (Sudham et al., 1990; Srivastava et al., 1991; Bowman et al., 1992; Ferrero et al., 1994; Harikrishnan et al., 1996) against rabbit ear mites — Psoroptes cuniculi. The aim of this study was to evaluate the efficacy of moxidectin in the treatment of scabies and demodicosis in dogs and Psoroptes spp. mite infestation in rabbits.