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Gnasthostoma in Dogs

What is gnathostoma spinigerum?

Gnasthostoma spinigerum is a parasitic roundworm that lives in the stomach and can infect dogs, cats, and pigs. It is not common and is found primarily in hot, humid areas of the United States, including the South (Florida, Georgia, Mississippi, Louisiana, Texas, and Alabama).

What is the life cycle of gnathostoma spinigerum?

Gnathostoma worms have a complex, indirect life cycle with at least two intermediate hosts and dogs, cats, pigs and other carnivores as their final hosts. Copepods (microscopic crustaceans also known as water fleas) are their first intermediate hosts. Several vertebrates (animals with backbones including fish, snakes, and frogs) are their second intermediate hosts. Birds, rodents, amphibians, snakes, and other vertebrates can also serve as transport hosts (these are known as paratenic hosts) after eating the second intermediate host. Transport hosts can carry the parasite encysted in the body (thus “transporting them”) but the worms won’t fully develop and finish their life cycle in these hosts and must be eaten by their final host species (dogs, cats or pigs) to finish their life cycle and lay eggs.

Eggs shed in the stools of infested final hosts (dogs, cats or pigs) release first stage larvae into the water. Water fleas (Copepods) eat the larvae, which then complete development to second stage larvae inside the first intermediate host (Copepod). Freshwater fish, snakes or frogs eat the infected water fleas releasing the second stage larvae into the second intermediate host. These second stage larvae continue development to third stage larvae and migrate into the flesh of the second intermediate host where they encyst.

When a final host (dog, cat, or pig) eats a second intermediate host, the encysted larvae are released. At that point, two things may occur. The third stage larvae may penetrate deeply into the stomach wall where they complete development to adult worms and reproduce. Or they may migrate through various organs (possibly the skin, liver, lungs, rarely the eyes or central nervous system tissue such as the spinal cord or brain) eventually returning to the stomach in 3 to 6 months. It is possible for third stage larvae to bury themselves in the stomach wall and cause the formation of tumor-like cysts filled with fluid and blood that may contain several adult worms. These cysts may remain within the lining of the lumen of the stomach or move into the peritoneal cavity (abdominal cavity) through a fine tube.

Alternatively, a second intermediate host can be ingested by a transport host (birds, rodents, reptiles) where the encysted third stage larvae do not complete development but wait until a final host eats the transport host. These larvae often migrate through various organs in the paratenic host before becoming encysted again.

What are the symptoms of gnathostoma spinigerum?

In dogs, gnathostoma infections can cause stomach inflammation and a decreased appetite. More serious symptoms occur when the nodules in the stomach burst and stomach contents leak into the abdominal (peritoneal) cavity. This can cause a severe peritonitis (inflammation of the lining of the abdominal wall or peritoneum) that can lead to sepsis (blood poisoning) and be fatal for the affected dog. Although not very common, migrating larvae can seriously damage internal organs (kidneys, liver, spleen) or affect the central nervous system and cause specific symptoms related to the loss of function of the affected organs.

While Gnathostoma worms are not normal human parasites they are a zoonotic concern (can infect humans and cause symptoms) and can be very harmful to humans. Larvae migrating through the skin (cutaneous larva migrans) cause skin inflammation (dermatitis) that can be painful and itchy. Larvae migrating through internal organs (visceral larval migrans) will cause symptoms based upon whatever organ they migrate through. Human fatalities are possible if gnathostoma larvae get into the central nervous system of a person.

What are the causes of gnathostoma spinigerum?

A frequent source of infection for dogs is the consumption of raw or poorly cooked fish (the second intermediate host), chicken or duck (paratenic or transport hosts). This is more common in some Asian countries where raw fish is a major part of the diet. Fish should be boiled at least 5 minutes to kill the larvae, or pickled for at least 6 hours in a mixture of vinegar (water and acetic acid).

Although the eggs in the feces of infected dogs and cats are not directly contagious for humans, such eggs can contaminate ponds or fountains that may contain water fleas (Copepods) that act as intermediate hosts. Dogs, cats, and humans can acquire the infection if they drink water contaminated with infected Copepods.

How can gnathostoma spinigerum be diagnosed?

A tentative diagnosis may be based upon symptoms, but identification of eggs in the feces of an infected dog allow a definitive diagnosis.

What are some treatment options for gnathostoma spinigerum?

As of yet, there are no reports on resistance of Gnatosthoma worms to appropriate wormers, but common wormers for pets are not approved and labeled for use against Gnathostoma worms. Some benzimidazoles (albendazole) and macrocyclic lactones (ivermectin) are effective against these worms, but the appropriate dose and treatment regime has to be determined by a veterinary doctor. 

If a wormer is ineffective, chances are very high that either the wormer was inappropriate for the control of Gnathostoma worms, or the wormer was not given as directed.        

How can gnathostoma spinigerum be prevented?

Prevention of a gnathostoma infection is by feeding properly cooked meat and fish, and not allowing dogs to eat raw meat or fish, or drink from freshwater ponds or pools in areas where the parasite may be found.

Prognosis

A dog’s prognosis will depend on upon where the worm is found in the body and whether treatment is started before serious damage is done. If the worms have migrated to the central nervous system, led to organ failure, or caused peritonitis or sepsis, then the prognosis may be grave (poor chance of a return to normal health). But if the only symptom is mild gastritis and the worms haven’t traveled past the stomach lining in the dog then the prognosis is very good.

 

About the Author:

Dr. Kara has been an Expert on JustAnswer since 2010 with over 12,943 satisfied customers.


Dr. Kara, Veterinary Expert

Dr. Kara graduated from Michigan State University. She is a member of the American Veterinary Medical Association, (AVMA), has over 20 years of experience in practicing small animal and pocket pet medicine. With emphasis on preventative care, internal medicine, and behavioral issues, Dr. Kara is also active with Greyhound rescue. While rescuing Greyhounds as pets, she strives to work with owners to tailor a plan to fit their personal lifestyle while minimizing the risk of exposure to disease for the pet.

Her interests and hobbies include international travel, hiking, reading, spending time with her husband and two children. 

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