Gnathostoma (Stomach Parasite) in Dogs

While rare, gnathostomiasis can be found in dogs in Africa, Asia, Australia and Southern Europe and is particularly common in feral dogs in parts of Southeast Asia.

Gnathostoma have a complicated life cycle. The adult worm will produce microscopic eggs in the stomach of a carnivore that is infected and these tiny eggs will exit the animal through his feces. Should these eggs make it to a water source, they will hatch and free-swimming larvae will be released. The larvae are then consumed by a water flea, where they are able to continue to develop. When a fish eats a water flea that is infected with these larvae, the larvae are able to grow to their immature form. Fish that are infected are often then eaten by another fish, frog, turtle, or bird and the larva is able to continue to develop in this new host. In fact, the larva can go through many hosts in the water until a dog eats an infected water animal.

Should the larva arrive in a dog’s stomach it can burrow through the stomach wall and travel to the liver, muscles and connective tissues, causing significant tissue damage. The larva will return to the dog’s stomach after about three months and attach to his stomach wall. A nodule will form around the worm who can grow to 10-50 mm in length. Eggs can then be laid by the adult worm and released in the dog’s feces.

Gnathostoma spinigerum, a species of Gnathostoma, is a parasitic nematode worm that infects the digestive tract of dogs causing the condition gnathostomiasis.

Dogs infected with gnathostoma may or may not show symptoms of infection. Symptoms may include:

• High temperature
• Tissue damage
• Swelling
• Pain

Symptoms will differ in severity based on the level of tissue damage. In some cases, an infected dog may vomit or display signs of redness. In more severe cases, the central nervous system of the dog is infected. The stomach lining of the dog may become inflamed and in rare cases rupture.

Types 

While humans can be infected by gnathostoma, they cannot catch it from a dog, only through eating raw or undercooked fish that has been infected by the parasite. Unlike in dogs, the parasite will not reach maturity in a human, however the larval form can lead to ulceration in the skin and eye damage.

Infection can differ in regards to levels of severity. On occasion, the nodule that develops around the maturing worm will rupture the stomach wall, which will lead to stomach contents leaking into the abdominal cavity of your dog. This can cause peritonitis in your dog, which can cause fever and abdominal pain and can be fatal.

Gnathostomiasis occurs due to the gnathostoma parasite being transmitted to your dog through his ingestion of infected raw flesh (usually fish). After your dog has consumed flesh infected by the parasite, the larva will arrive in his stomach, where it will tunnel through his stomach wall and travel to his liver, muscles and connective tissues, leading to tissue damage of varying severity; symptoms will vary and are dependent on the location of the larva.  After three months the larva will travel back to your dog’s stomach and attach to the stomach wall, developing a nodule around itself while it matures.

Your veterinarian will conduct a physical examination of your dog to understand any clinical signs or symptoms that your dog is experiencing and ask you what symptoms you have noticed and when you first noticed them. It is likely your veterinarian will ask questions about your dog’s medical history in order to rule out any other possible causes of his symptoms. You will want to consider if your dog has had any opportunities to ingest uncooked fish, reptiles or other animals that could have been infected with gnathostoma, leading to a possible infection. Your veterinarian will likely take a fecal sample so that he can confirm the presence of the parasite in your dog.

Infection is rare and because of this there is not a lot of knowledge as to how to resolve it. The medication albendazole, an anti-helminthic drug, may be a possible treatment option. Surgery can also be considered where the parasites will be physically removed from your dog.

Should your dog be infected with gnathostoma, your veterinarian will advise you on how to best assist in his recovery and when to return for follow up visits. 

It is recommended that you keep your dog from eating raw fish in order for him to avoid developing an infection. This includes ensuring that any fish you keep as pets are inaccessible to your dog, as these fish have been known to cause the infection in dogs.