- Dr Chiraag Simao, BVSc
Spirocercosis - the silent killer strikes again!
What is it?
Spirocerca Iupi is a type of worm called a nematode which is a round worm. The worm causes a disease in dogs called Spirocercosis. The clinical signs of the disease are as a result of the migration of the worm within the body of the host (the infected dog) through the wall of the stomach into the aorta and finally into the oesophagus (commonly known as the food pipe) where the adult worm persists and lays eggs (Fox et al. 1988, Van der Merwe, 2008).
Where is it found?
The worm has a worldwide distribution, occurring in warmer tropical climate areas (Bailey, 1972). The distribution is not evenly spread out and it occurs in pockets across the world (Bailey, 1972). South Africa is one such place in which the worm is found. In South Africa the distribution is again not evenly spread with the worm being prevalent in specific areas of the country such as Kwa-Zulu Natal, Northern Gauteng and parts of the Eastern Cape (Lobetti, 2000). One of the reasons for this patchy distribution relates to the occurrence of the dung beetle alongside dogs (Bailey, 1963). Specific dung beetle species are the intermediate host for the worm meaning that part of the lifecycle (the immature larval stages) needs to occur inside the dung beetle. These dung beetles are then ingested by the dog where the worm (in its 3rd and infective larval stage) further develops into an adult (Fox et al, 1988). Dogs may also become infected if they ingest transport hosts (aka paratenic hosts) such as birds, amphibians, reptiles and small mammals who have already ingested an infected beetle (Fox et al. 1988, Van der Merwe, 2008).
Why does it matter?
The worm can cause sudden death in a dog that appears to be otherwise healthy hence why it can be referred to as the silent killer. It can affect any breed or age and even well-cared for pets that are vaccinated can become victim (Lobetti, 2014). Once the dog ingests the infected dung beetles containing the infective stage (3rd larval stage-L3) the worm is released in the stomach and penetrates through the stomach wall (Bailey 1972, Van der Merwe 2008).
This irritation to the stomach lining may induce bouts of vomiting. However, this first sign can easily be missed and the worm easily goes undetected and continues to migrate in the blood vessels of the stomach lining to the aorta (Lobetti, 2014). The aorta is the major blood vessel carrying blood from the heart to the entire body. Aneurysms (localized areas of vessel wall ballooning as a result of weakening of the wall) can occur in the aorta when the immature worms continue to migrate from the aorta into the adjacent oesphageal wall, which is where the worm lives as an adult (Lobetti, 2014). In some cases the aorta wall will rupture at one of these weak points in the wall causing sudden death as a result of blood leaking out into the body cavity.
Should this not happen the infected dog still develops a horrible disease that may cause severe illness and eventual death if not treated early.
What are the signs of disease?
The signs of spirocercosis are, as mentioned already, as a result of either the migration of the worm through the body (stomach and aorta) or residence in the oesophagus. These signs include weight loss, salivation and difficulty swallowing (Fox et al. 1988). When the worm resides in the aorta there are no signs unless rupture occurs (associated with the migration of the worm through the vessel wall), whereupon haemothorax (blood filling the thoracic cavity) and sudden death may take place. When the worm resides in the oesphageal wall it causes irritation of the wall and this results in inflammation of the wall and the formation of a nodule called a granuloma which is an accumulation of scar tissue (Lobetti, 2014). This granuloma/nodule is what causes the signs of coughing, difficulty swallowing and, as it keeps growing, it causes regurgitation because it creates an obstruction to food that needs to pass through.
These signs persist and result in weight loss. In some cases the oesophageal nodule can undergo malignant transformation to form a cancerous tumour called a sarcoma which may spread throughout the body (Bailey 1963, Ivoghli 1978). Spondylitis (inflammation) of the thoracic vertebra also occurs with this disease (Fox et al, 1988). There are also times where worms have aberrant migrations and flow through blood vessels and lodge in different organs such as lungs, kidneys and even vertebra or skin (Reinecke 1983).
How is spirocercosis diagnosed?
Diagnosis is mostly done using chest radiography to visualize the nodular mass in the oesophagus. This however does not exclude a possible infection that is still in the very early stages. After a dog has ingested the infective worm larvae (i.e. L3 present in the dung beetle or other infected paratenic host) it takes up to 3 months to complete the internal migration, as young adults, to the oesophagus and form nodules (Van der Merwe et al, 2008). During this time it is extremely difficult to detect the worm as the there are no other signs or lesions that are obvious. Another very powerful diagnostic tool is endoscopy which involves visualizing the nodules. Eggs that shed in the faeces (stool/dung) of the infected dog can also be used to diagnose the disease.
Examining the faeces of an infected dog, however, is not very reliable as the eggs are only shed when the adult female is able to lay eggs into the oesophagus through an opening in the nodule. This laying of eggs happens sporadically. Another challenge with examining the faeces is that the eggs are very small in relation to other worm eggs and very difficult to visualize. In addition to this the technique used to examine faeces for worm eggs is not ideal for detecting Spirocerca lupi eggs as these eggs are heavier and sink to the bottom of the flotation medium, when they are required to float to the top to stick onto a cover slide for visualization under a microscope (Lobetti, 2014; Van der Merwe, 2008). Unfortunately, the disease is often diagnosed when it is too late and the nodule is too large to remove or treat (Lobetti, 2014). Surgical removal of large masses in the oesophagus is not an option because of the poor healing of the tissues and poor recovery. Often times the only option, as sad as it is, is humane euthanasia in such cases.
What is the treatment and prevention of spirocercosis?
Not all deworming medications given are effective against this specific worm. The only oral medication that is registered for the treatment and prevention of the worm is Milbemax Chewable tablets. These tablets are given according to body weight of your pet and prevent all types of worm infections (both Cestodes and Nematodes) which includes Spirocerca, hookworms and tapeworms. The deworming has to be done every 28 days to ensure that if your dog does pick up the worm it is protected from developing the nodules (Kok et al, 2011). It is also extremely important to pick up all pet droppings as soon as possible to avoid reinfection. If you live in an area where the disease is common proper deworming, using the right product, becomes vital. It is advisable to speak to your veterinarian to further understand the disease and how to keep your pets safe.
Bailey, W.S., 1963, ‘Parasites and cancer: Sarcoma associated with Spirocerca lupi’, Annals of the New York Academy of Sciences 108, 890–923. http://dx.doi.
Bailey, W.S., 1972, ‘Spirocerca lupi: A continuing inquiry’, Journal of Parasitology 58,3–22. http://dx.doi.org/10.2307/3278233
Fox, S.M., Burns, J. & Hawkins, J., 1988, ‘Spirocercosis in dogs’, Compendium on Continuing Education for the Practicing Veterinarian 10, 807–822.
Kok, D.J., Williams, E.J., Schenker, R., Archer, N.J. & Horak, I.G., 2010, ‘The use of milbemycin oxime in a prophylactic anthelmintic programme to protect puppies, raised in an endemic area, against infection with Spirocerca lupi’, Veterinary Parasitology 174, 277–284. http://dx.doi.org/10.1016/j.vetpar.2010.08.029
Lobetti, R., 2000. Survey of the incidence, diagnosis, clinical manifestations and treatment of Spirocerca lupi in South Africa. Journal of the South African Veterinary Association 71, 43–46.
Lobetti, R., 2014 http://www.jsava.co.za doi: 10.4102/jsava.v85i1.1169
Ivoghli, B., 1978, ‘Esophageal sarcomas associated with canine spirocercosis’,Veterinary Medicine and Small Animal Clinician 73, 47–49.
MILBEMAX™ Chewable Tablets for Puppies and Small Dogs 1-5 kg. Reg. No.: G3834 (Act 36/1947). Milbemycin oxime (2,5 mg); Praziquantel (25,0 mg). MILBEMAX™ Chewable Tablets for Dogs more than 5 kg. Reg. No.: G3833 (Act 36/1947). Milbemycin oxime (12,5 mg); Praziquantel (125,0 mg).
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