Responsible for an increase in oesophageal cancer in dogs, Spirocerca lupi (from here on out referred to as “S. lupi“) is a parasitic worm that causes a disease known as Spirocercosis in dogs. Not given much thought until relatively recently, this worm has become of prime concern to veterinarians and pet owners around South Africa. Over the last decade we have seen a dramatic increase in prevalence of S. lupi related cases in South Africa, particularly in summer rainfall areas. We therefore recommend that if you don’t know about the worm already, you take the time to learn about it now.
Spirocercosis
Infection occurs when a dog ingests the infectious larval stage of the worm by eating certain species of dung beetle. These worm larvae then migrate up the stomach arteries, through the aortic wall, and into the oesophagus where they form nodules. These nodules are responsible for the main clinical signs of S. lupi which include regurgitation and coughing. Other clinical signs include weight loss, salivation, difficulty swallowing, pain during eating, anaemia and fever.
Sudden death can occur due to a ruptured aortic aneurysm – the result of damage caused by the worms during their migration through the arteries. The oesophageal nodules are also known to undergo malignant changes, leading to cancer of the oesophagus.
Large breed dogs between the ages of one and four years seem to be the highest risk group for contracting this parasite.
Diagnosis
Diagnosis of Spirocercosis requires chest x-rays and endoscopy of the oesophagus. Worm eggs can sometimes be seen on faecal flotation, however, they are very small and require a specialised flotation fluid.
Treatment
Treatment involves the use of drugs belonging to the class of macrocyclic lactones and the most commonly used active ingredient is Doramectin. Many of these products are not registered for use in dogs and are therefore used “off-label”. They include weekly treatment with injections, tablets or “top spot” preparations. These treatments will kill the adult Spirocerca worms inside the nodules, however, they will not reverse damage to the aorta or any cancerous changes to the oesophageal wall. Prevention of the parasite is therefore much safer and more effective than treatment once disease has occurred.
A product called Advocate ® has recently been launched to aid in the prevention of S. lupi. It is a spot-on formulation that is applied monthly to the dog’s skin that contains active ingredients to prevent fleas, as well as spirocerca and other roundworm infections. It is recommended that all puppies from the age of 7 weeks are started on monthly Spirocerca preventative to avoid this devastating disease.
Please note than in KwaZulu-Natal, we have a low number of dogs that carry a non-pathogenic (non-disease causing) worm called Dirofilaria repens in their blood streams. This worm is harmless in itself, however, if large numbers of these worms die after the treatment of infected dogs with a macrocyclic lactone product, they release proteins into the dog’s bloodstream which can result in a life-threatening allergic reaction. Infection with D. repens can be confirmed or ruled-out with a blood test called a Knotts test. Although the risk of reaction is very low, the reaction is very serious and we do occasionally get dogs that test positive on a Knotts test. It is recommended (but not compulsory) that a Knotts test be performed on all adult dogs prior to starting S. lupi preventative or treatment.
For more information on S. lupi, feel free to contact Equis Veterinary Hospital on 031 769 1072.