Spirocerca lupi in dogs: prophylactic effect of doramectin

Spirocerca lupi is primarily a parasite of dogs, which typically causes oesophageal nodules, aortic aneurysms, and spondylitis. This study investigated the efficacy of doramectin as a prophylactic agent for canine spirocercosis. Five beagle dogs were injected subcutaneously with doramectin (400 microg/kg on 3 occasions 30 days apart q30d), while 5 other beagle dogs served as untreated controls. All dogs were inoculated with 40 infectious S. lupi larvae (L3) one month after the last doramectin treatment. All control dogs and 4/5 treated dogs became infected. Two control dogs died of ruptured aortic aneurysms, while no deaths occurred in treated dogs. Oesophageal nodules appeared 40-103 day later in treated as compared to control dogs, and eggs appeared in the faeces 49-106 day later in treated as compared to control dogs. The mean faecal egg count on day 223 in the treatment group was reduced by 99.77%. All control dogs had thoracic radiographic changes during the study, while only 2/5 study dogs showed radiographic changes. This study shows that although doramectin did not entirely prevent canine spirocercosis it reduced the clinical signs associated with infection and delayed and reduced egg output.