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Gnathostomiasis

Last updated Sept. 17, 2018

Approved by: Krish Tangella MD, MBA, FCAP

Gnathostomiasis is a rare, food-borne infection, caused by a species of parasitic worms (nematodes) called Gnathostoma.


What are the other Names for this Condition? (Also known as/Synonyms)

  • Gnathostoma Worm Infection
  • Larva Migrans Profundus
  • Nodular Migratory Eosinophilic Panniculitis

What is Gnathostomiasis? (Definition/Background Information)

  • Gnathostomiasis is a rare, food-borne infection, caused by a species of parasitic worms (nematodes) called Gnathostoma
  • Two species of Gnathostoma can cause infection, namely Gnathostoma spinigerum and Gnathostoma hispidum. Nevertheless, the former is more likely to cause infection in humans than the later
  • The transmission of infection occurs by eating undercooked or raw freshwater fish, frogs, eels, birds, or reptiles. The infection is most common in Southeast Asia. However, Gnathostomiasis cases have been reported in other parts of the world
  • The affected individuals develop swelling/bulges under the skin that can migrate to various locations on the body. On rare occasions, the parasite can enter the liver, eye, nerves, spinal cord, or brain, causing severe complications
  • Blood tests are the chief mode of diagnoses for Gnathostomiasis. The infection is treated with prescription medications or surgery, to remove the worm following a diagnosis
  • Since the infection spreads from consumption of raw/undercooked meat, cooking meat adequately is the best way to prevent one from being infected
  • The outcomes are good for Gnathostomiasis, since the infection can be successfully treated with proper clinical care

Who gets Gnathostomiasis? (Age and Sex Distribution)

  • Gnathostomiasis is a rare, food-borne infection. It can occur in individuals of all ages and both genders, without racial or ethnic predilection
  • Southeast Asia is the most common region where the prevalence of many Gnathostomiasis cases are noted. However, cases have been reported from South and Central America, Africa, and other parts of Asia too
  • Individuals in many developed nations (such as the United States) typically do not develop Gnathostomiasis, unless the infection sets in from travel to the affected regions

What are the Risk Factors for Gnathostomiasis? (Predisposing Factors)

The risk factors for developing Gnathostomiasis include the following:

  • Ingesting undercooked or raw freshwater fish
  • Eating other raw or undercooked animals found in freshwater. Examples of such animals include:
    • Frogs
    • Eels
    • Some reptiles and birds
  • Living in tropical or subtropical areas of the world (such as Southeast Asia), where an individual may be exposed to infected animals

Note: Fish from saltwater is generally not infected by Gnathostoma.

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases one’s chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Gnathostomiasis? (Etiology)

Gnathostomiasis is caused by an infection of the parasite Gnathostoma, especially Gnathostoma spinigerum.

  • Gnathostomiasis can develop in humans after consumption of raw or undercooked meat from freshwater fish, frogs, eels, reptiles, and birds 
  • These animals are susceptible to infection, which can be transmitted to humans when they eat fish or meat contaminated with Gnathostoma larvae
  • Larva entering the body grow and migrate within the body, causing the characteristic symptoms associated with this infection

What are the Signs and Symptoms of Gnathostomiasis?

The movement of parasite through the body is believed to be the cause of symptoms of Gnathostomiasis. The affected individuals may not exhibit any symptom of infection, or can show varying signs, depending on where the parasite is situated at any given time.

  • In the early phase of infection, typically 24 to 48 hours after ingestion of Gnathostoma, when the parasite is moving through the wall of the stomach, intestine or liver, the signs and symptoms may include:
    • Fever, tiredness
    • Abdominal pain
    • Lack of appetite
    • Flushing, itching, skin rash
    • Nausea and vomiting; diarrhea
    • Increased eosinophil count in blood. Eosinophils are a type of white blood cells that are critical in fighting parasites or infections
  • If the parasite moves under the skin at a later stage (typically 3-4 weeks after infection; but, this may even occur up to 12 years later, due to a lack of treatment), the symptoms may include:
    • Painful, red, or itchy swellings under the skin that can move around to different locations on the body
    • No indentation left on the skin, if pressure is applied
  • If the parasite enters the lungs, the symptoms may include:
    • Blood-streaked sputum, or fluid in the lungs  
    • Pneumothorax, or collapsed lung 
  • If in the eye, the symptoms include vision loss or blindness 
  • If it involves the spinal cord or nerves, the symptoms include:
    • Severe nerve pain
    • Paralysis in muscles that are controlled by the affected nerve
  • If it involves the brain, the symptoms include:
    • Headache
    • Decreased consciousness
    • Coma 
  • Symptoms can arise from any organ or tissue that is infected. But, lung, eye, spinal cord, and brain infections are usually rare
  • Generally, invasion of the brain or eye is more likely in individuals that have a parasite moving under the skin of the face

How is Gnathostomiasis Diagnosed?

The diagnosis of Gnathostomiasis is made through the following tests and exams:

  • A complete physical examination and review of medical or travel history. This involves questioning the affected individual about recent consumption of raw or undercooked freshwater fish, frogs, eels, reptiles, or birds, in a part of the world endemic to Gnathostoma
  • Assessment of symptoms
  • Analysis of blood samples in certain specialized labs
  • Recovery and analysis of an infecting worm through surgical measures to determine its species

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Gnathostomiasis?

Complications of Gnathostomiasis depend on where the parasite is located in the body.

  • Infection of the parasite may persist within the body for up to 12 years, if left untreated
  • Swelling of the skin and formation of rashes intermittently (over time), with movement to any location in the body 
  • Severe complications following an organ infection can also result in death

How is Gnathostomiasis Treated?

Treatment options for Gnathostomiasis include: 

  • Anti-parasitic medication to eliminate the parasitic worm 
  • Surgery to remove the infecting worm: This procedure can be difficult, because it may be difficult to locate the position of the worm in the body. A surgical removal of the parasite does not always cure Gnathostomiasis, but is considered the best treatment option

How can Gnathostomiasis be Prevented?

The following are some tips for prevention of Gnathostomiasis: 

  • Avoiding the consumption of any raw or undercooked freshwater fish, frogs, eels, reptiles, or birds, in parts of the world where Gnathostomiasis is known to commonly occur
  • Avoiding contaminated freshwater where Gnathostoma is common
  • Washing hands with soap and warm water before preparing food
  • Wearing gloves, if handling raw meat from animals that are susceptible to infection
  • Cooking fish to an internal temperature of at least 145° F, as suggested by the US Food and Drug Administration (FDA)

What is the Prognosis of Gnathostomiasis? (Outcomes/Resolutions)

The prognosis of Gnathostomiasis is generally positive with proper treatment. The outcomes of Gnathostomiasis can include the following: 

  • With treatment, Gnathostomiasis can be cured successfully
  • If left untreated, infecting Gnathostoma may live and migrate through the tissues of the body for up to 10-12 years. The effect and severity of the parasitic infection will depend on where it is in the body
  • Severe complications and even death may occur, if the parasite infects the spinal cord or brain. However, this is very rarely noted

Additional and Relevant Useful Information for Gnathostomiasis:

  • Many species of Gnathostoma exist inside of animals located all over the world (including some animals in the United States), but only Gnathostoma spinigerum and less commonly Gnathostoma hispidum are known to cause infection in humans. These species are found only in tropical and subtropical locations
  • The adult parasite can be found in the stomach of cats, dogs, or wild cats including tigers and leopards. Other wild animals can also carry the parasite
  • The first tiger that was discovered to have G. spinigerum in its stomach was one that had died in a London zoo in 1836. To this day, it is not known how a tiger in London became infected with a worm found in Southeast Asia
  • The first human case of Gnathostomiasis was described in 1889, and it was not until 1934 that more human cases were reported. By this time, more information on which type of animals were prone to infection and how they were infected was available
  • Gnathostomiasis was first detected in South America in Ecuador in 1979, and in 1985, it was found that dogs and cats could be hosts to the Gnathostoma parasite in South America as well. Prior to these discoveries, only countries in Southeast Asia were known to have cases of Gnathostomiasis 
  • Countries, like the United States, have a low incidence of Gnathostomiasis because more saltwater fish are consumed and stricter regulations on seafood are typically followed
  • Humans are not natural hosts for the parasite, and it cannot develop fully into its adult form inside the human body. This causes the parasite to grow and migrate through tissues for up to 12 years, if no treatment is given. Typically, only one worm infects a human at a time

What are some Useful Resources for Additional Information?


References and Information Sources used for the Article:


Helpful Peer-Reviewed Medical Articles:


Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: Aug. 4, 2017
Last updated: Sept. 17, 2018