The efficacy of milbemycin oxime against pre-adult Spirocerca lupi in experimentally infected dogs.

The aim of this investigation was to determine the efficacy of milbemycin oxime in preventing the oesophageal encapsulation of Spirocerca lupi, following the experimental infection of dogs. Two studies were conducted which involved a total of 21 purpose-bred Beagles. Each dog was infected with approximately 40, third stage infective S. lupi larvae. The larvae were dissected from scarabaeid beetles that had been collected from areas endemic for spirocercosis. In the first study, milbemycin oxime (minimum dose 0.5mg/kg body weight) was administered to seven dogs on day 30 post-infection. Seven other dogs served as untreated controls. In the second study, milbemycin oxime (also at a minimum dose of 0.5mg/kg body weight) was administered to four of seven infected dogs on day 28 post-infection. Treatment was repeated at 14- or 28-day intervals. All of the dogs, from both studies, were euthanized 168 or 169 days after infection. All S. lupi were recovered, and lesions in the thoracic aorta and oesophagus were described and quantified. A single treatment with milbemycin oxime was 79.8% effective in preventing the establishment of S. lupi in the oesophagus. This treatment significantly (p<0.05) reduced both the number of S. lupi within the oesophagus and the size of the oesophageal nodules. The efficacy of anthelmintic treatment was increased to 100% when repeat doses of milbemycin oxime were administered at 14- or 28-day intervals. These repeat treatments completely prevented the establishment of S. lupi within the oesophagus and thereby averted the development of oesophageal nodules. As expected, none of the treatment protocols reduced S. lupi related damage within the aorta because the administration of milbemycin oxime only began after the larvae had completed their first stage of migration.

The use of milbemycin oxime in a prophylactic anthelmintic programme to protect puppies, raised in an endemic area, against infection with Spirocerca lupi.

Spirocerca lupi is primarily a parasite of dogs and other carnivores. Clinical signs of infection are regurgitation, vomiting, weight loss, coughing and dyspnoea. Sudden death can also occur due to a ruptured aortic aneurysm. In this study, the Eastern Cape Province of South Africa was identified as an area with a high prevalence of S. lupi. A subsequent investigation, to evaluate the efficacy of milbemycin oxime as a prophylactic agent for canine spirocercosis, involved 58 puppies that were raised in this area in accordance with local husbandry procedures. Approximately half of the puppies served as untreated controls. Puppies in the treatment group received milbemycin oxime (minimum dose of 0.5mg/kg body weight) when they were between 2 and 6 weeks old. They then received five further treatments at approximately 28-day intervals. The treatment was orally administered in tablet form. After the sixth treatment, puppies from both the treated and control groups were euthanized and post-mortem examinations were performed. Twenty-four out of 27 dogs in the untreated control group had become infected by S. lupi. In comparison, only 19 out of 31 dogs in the treatment group had evidence of spirocercosis as demonstrated by aortic nodules. The prophylactic regimen reduced the severity of aortic lesions and prevented 86.5% of S. lupi from becoming established in the thoracic aorta. It also prevented 89.4% of S. lupi from becoming established in the oesophagus and significantly reduced the number of oesophageal nodules. Milbemycin oxime markedly reduced the level and severity of S. lupi infection in treated puppies raised in an endemic area of South Africa. It deserves further evaluation as a potential prophylactic treatment for spirocercosis.