The nematode Spirocerca lupi is primarily a parasite of dogs, which causes typical lesions of esophageal nodular
granulomas,
aortic aneurysms and
spondylitis. In order to evaluate the
therapeutic effect of
doramectin on experimental canine spirocercosis, seven beagle dogs experimentally infected with 40 infectious S. lupi larvae (L(3)) were treated with
doramectin. Treatment was commenced following endoscopic visualization of esophageal
granulomas, and typical S. lupi eggs were detected in the feces. The treatment protocol included six treatments of
doramectin (400 microg/kg subcutaneously) at 2 weeks intervals, followed by monthly
injections until the disappearance of the esophageal
granulomas or the end of the study (768 days post-inoculation). Eggs could not be found on fecal examinations 3-10 days after the first or second
doramectin treatment. In addition, a gradual decrease in size of
granulomas was noticed in all seven dogs during the course of the study. Esophageal
granulomas had completely resolved in six of the seven dogs between day 35 and day 544 post-initial
doramectin treatment, by day 35 in one dog (after three treatments), by day 43 in two dogs (after four treatments), by day 98 in one dog (after seven treatments), by day 460 in one dog (after 18 treatments) and by day 544 in another dog (after 21 treatments). In one dog, remnants of S. lupi
granulomas could still be seen 544 days post-initiation of treatment with
doramectin. Multiple
subcutaneous injections of
doramectin (400 microg/kg) were shown to be effective and safe in the treatment of canine spirocercosis.