Spirocercosis – Dr Dave Miller, Dr Liesel Van der Merwe
Spirocerca Lupi
Written by:
- Dr Dave Miller, Johannesburg Specialist Veterinary Centre
- Dr Liesel Van der Merwe , Onderspoort Veterinary Academic Hospital
Spirocerca lupi (S. lupi) is a worm that has dogs as its definitive host and forms a nodule (“granuloma”/mass) within the lower oesophagus (“slukderm”).
The worm:
It is a large± 5cm long red worm that lives inside the oesophagus (slukderm) of the dog. It forms a large nodule in the oesophagus which usually results in the symptoms experienced. The dog is infected after eating a dung beetle or other infected animal (lizard or bird that has eaten the dung beetle). The term spirocercosis is used to describe the disease in the dog.
The life cycle:
A final host (dog) and an intermediate host (dung beetle) are needed to complete the life-cycle. The adult S. lupi lives within the oesophagus where it irritates the normal tissue. The irritated tissues then seep tissue fluid and this is what the adult worm lives on. The irritated tissue, in the oesophageal wall, enlarges/ hypertrophies and lays down fibrous tissue and forms a nodule that is often incorrectly called a granuloma. When the worm is adult it lays eggs through a hole in the mass [operculum] and the eggs pass through the intestines and are passed in the dog’s faeces (stool). The infected dog passes out large numbers of eggs into the stool. Dung beetles then eat the stool and in turn become infected.
The eggs hatch to larvae within the beetle and are infective to dogs if eaten.
This worm also uses other hosts to carry the infective larva. These hosts are called “transport” hosts. These include birds, mice, lizards and frogs. They become infected when they eat a dung beetle containing a Spirocerca lupi larva. The larva does not develop further inside these hosts, nor does it harm them, but still remains infective to dogs that eat these transport hosts.
Once ingested: the larvae hatch inside the stomach of the dog and start a migration path to the oesophagus. They first migrate along the abdominal blood vessels to the aorta. Here the larvae develop into young adults. Once they are mature enough, they start to move forwards inside the aorta and then they migrate towards the oesophagus through the tissues in the chest. This process usually takes 4 to 6 months but can be as fast as 2 ½ months. Once in the oesophagus, they form a large nodule in which they live. The female worms then pass eggs out through a small opening. Eggs then pass through the intestinal tract and are deposited with the stool of infected dogs. Dung beetles eating this stool become infected, the life cycle continues.
Clinical signs in the dog:
Due to the nodule (Irritation of the oesophageal wall, Irritation of the nerves, physical obstruction):
- Vomiting and/or Regurgitation
- Change in breathing (panting, coughing, retching)
- Sialoadenosis – Increased salivation and enlarged salivary glands
- Weight loss
- Fever
- Lethargy/ Weakness (can be due to: not keeping food down or the nodule becoming cancerous or due to anaemia)
- Pale gums and lips – due to bleeding from nodules
- Swollen feet (Maries disease/Hypertrophic Osteopathy)
Due to the migration through the dog:
- Fever
- Rupture of blood vessels – which may result in death
- Secondary bacterial infections
- Coughing/Pneumonia
- Due to Adults worms or Larvae forming nodules in the incorrect place:
- Coughing
- Paralysis (in spinal cord)
- Raised liver levels (nodule in liver)
The most common clinical signs reported in retrospective studies are respiratory signs, vomiting (active) or regurgitating (passive), acute death from a bleeding aortic aneurism, Maries disease (swollen feet) and sialoadenosis (a condition where the salivary glands enlarge). The nodule can also become cancerous and this cancer can then metastasize (spread) throughout the body.
Diagnosis of this disease:
This disease is not always that easy to diagnose and a number of methods can be utilized.
Faecal samples may show infection but only once the worm is mature in a nodule (4-6 months after infection).
X-ray photos (2 views of chest) can reveal the nodule in the oesophagus once it is over a certain size.
Endoscopy: The most successful method uses a camera that is passed down into the oesophagus and one can then visually inspect for the nodule. The risk of cancerous change is then assessed through biopsies taken thru the endoscope.
Computed tomography or CAT scan is a more sophisticated method of X- rays to diagnose the nodule in the oesophagus.
Once a definitive diagnosis is made then treatment for the disease can be undertaken. Advanced spirocercosis that has become cancerous and spread into the body cannot be cured but palliative therapy can be attempted.
Treatment:
Dogs with a simple infection/ small nodule often will respond to anti-parasitic drugs, which may be given by injection or by mouth. Repeated treatments over a time period are required. The re-evaluation of the oesophagus, through endoscopy, is required to ensure cure.
The drug used to treat this worm is a drug commonly used in livestock. It is not registered for use in dogs. Owners’ permission to use this drug is required. This drug can only be used in Border Collies, old English sheepdogs rough collies and Australia Cattle dogs and Australian Sheepdogs and Collie X dogs once a special PCR test has been performed to show that it is safe to use. In Collie type dogs that have an abnormal gene, one must try other deworming agents to try and cure the worm.
Killing the worm cannot cure clinical signs in dogs with nodules that have become cancerous. These dogs require surgical and medical treatment.
Prevention:
Two new products have been registered for the use of prevention and treatment of Spirocerca Lupi infections in dogs.
Milbemycin Oxime (Milbemax by Elanco)
Moxidectin & lmidacloprid (Advocate by Bayer)
Both these products need to be used MONTHLY for prevention purposes.
Please note that treatment doses for clinical cases differ dramatically and should be administered under the supervision of your veterinarian.
- Courtesy of Dr Dave Miller (BVSc, MMedVet (Med)), Johannesburg Specialist Veterinary Centre
- Dr Liesel Van Der Merwe (BVSc, MMedVet (Med)), Onderstepoort Veterinary Academic Hospital
