Efficacy of moxidectin equine oral gel against endoscopically-confirmed Gasterophilus nasalis and Gasterophilus intestinalis (Diptera : Oestridae) infections in horses

A 3 m, video gastroscope was used to screen 47 horses suspected of being na turally infected with equine hot larvae. 17 of 47 (36.2%) candidate horses harbored Gasterophilus nasalis larvae in the proximal duodenum and 46 of 47 (97.9%) had G. intestinalis larvae in the stomach. All horses infected wit h G. nasalis had concurrent infections with G, intestinalis. 14 horses with dual infections were allocated randomly to two treatment groups. Seven hor ses in Group 1 received 2% moxidectin oral gel once at a dosage of 0.4 mg/k g bodyweight (BW), and seven horses in Group 2 were untreated controls. 14 days after treatment, all horses were necropsied and the stomach and proxim al duodenum harvested from each. Bot larvae were recovered, identified to s pecies and instar, and counted. At the label dosage, moxidectin oral gel wa s 100 and 97.6% effective (P < 0.05) against third-instar G, nasalis and G. intestinalis, respectively. In addition to demonstrating the boticidal eff icacy of moxidectin, this trial illustrated that gastroscopy/duodenoscopy i s a feasible method for confirming infections with different species of bot larvae in the horse. (C) 2000 Elsevier Science B.V. All rights reserved.