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

• Heterophyes Heterophyes Infection

What is Heterophyiasis? (Definition/Background Information)

• Heterophyiasis is a parasitic infection caused by the fluke Heterophyes heterophyes. The parasite is typically found in Egypt and other areas of the Middle East and Asia
• Flukes are flat, leaf-like parasites that live inside the body of animals or humans. Fluke is the common name for any member of the class Trematoda
• H. heterophyes is an intestinal fluke, meaning that they live and attach themselves to the intestine of the host, after they are ingested. Humans can contract Heterophyiasis, if they consume undercooked or raw fish that contain larvae of H. heterophyes encased in a cyst (a type of shell)
• Once inside the body, the larvae exit the cyst and mature into adults. These adults live inside of the host’s intestine; but, they can also migrate around the body, to places like the heart and brain
• Abdominal pain and diarrhea are the most common symptoms of the infection. Severe complications can rarely occur if the parasites migrate to the heart or brain, which may even be fatal
• A microscopic examination of stool samples is the chief mode of diagnosis of Heterophyiasis. Following a positive diagnosis, the infection is treated with anti-parasitic drugs. The prognosis is good in most cases, with early diagnosis and prompt treatment

Who gets Heterophyiasis? (Age and Sex Distribution)

• Heterophyiasis is a common infection in regions where H. heterophyes is found, including
  • Middle East Asian countries (especially Egypt)
  • Philippines
  • Taiwan
  • Korea
  • China
  • Japan
• The infection occurs without any age, gender, racial or ethnic bias
• Individuals in the United States typically do not develop Heterophyiasis, unless the infection sets in from travel to the endemic regions

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

The risk factors for Heterophyiasis may include:

• Eating undercooked or raw fish that contains encysted (encased in a shell) H. heterophyes larvae. This stage of larvae is called the metacercaria stage
• Not washing hands after handling infected raw fish
• Not cleaning cooking utensils after preparing a meal containing infected fish
• Individuals with occupations, such as fishing, which can result in exposure to infected fish
• Living in areas of the world where H. heterophyes is prevalent

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 Heterophyiasis? (Etiology)

Heterophyiasis is caused by the liver fluke Heterophyes heterophyes.

• The infection occurs when a human or other animal consumes raw or undercooked fish infected with H. heterophyes cysts. Cysts are small shell-like structures that encase the developing larva
• Snails ingest the flatworm eggs, which hatch and produce larvae known as cercariae. The cercariae attach themselves to the skin of fish (fresh/brackish water), and embed themselves in the tissue in the form of cysts
• On ingestion of the larval cysts, the cysts surrounding the larvae dissolve. The larva then attaches itself to the walls of the small intestine
• There, they feed on nutrients, mature into adults, and lay eggs. The eggs are released from the body along-with feces, which are then ingested by snails
• The adult flukes irritate the area of infection and can migrate to other areas of the body (notably to the heart and brain) through the lympho-vascular system or bloodstream

What are the Signs and Symptoms of Heterophyiasis?

Many individuals with Heterophyiasis may not display any symptoms. However, significant symptoms are known to develop, especially in severe cases. The signs and symptoms may include:

• Abdominal discomfort
• Loss of appetite
• Chronic diarrhea that is slimy in appearance, occasionally containing blood
• Nausea and vomiting
• Inflammation at the site of infection  
• Ulcers
• Necrosis, a type of cell death, of the infected area

Occasionally, H. heterophyes can migrate from the intestines to other organs in the body, especially to the heart and the brain. The lungs and spinal cord are also possible destinations. This migration occurs through the circulation of blood or lymph (fluid that circulates along blood as part of the lymphatic system). On the rare occasions that this migration occurs, organ-specific symptoms can develop.

How is Heterophyiasis Diagnosed?

The diagnosis of Heterophyiasis is made through the following tools:

• A complete physical exam and review of medical/travel history
• Assessment of the presenting symptoms
• Analysis of a stool sample: The clinicians look at the stool sample under a microscope for the presence of characteristic mature eggs. It may, however, be difficult to distinguish eggs belonging to different species without obtaining a fluke from a tissue sample
• Blood tests: Blood is examined for eosinophilia, a condition showing an increase in the number of eosinophils (white blood cells that help the body fight infection or parasites), which is indicative of an infection
• Removal of infected tissue via surgery and analysis for the presence of parasites

Note: The condition can show multiple spots in lung and abdomen, which may be misdiagnosed as tuberculosis.

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 Heterophyiasis?

In a majority, Heterophyiasis is generally mild and may exist without significant symptoms or complications. However, severe infection can result in digestive system complications. Other complications may also arise owing to the migration of H. heterophyes from the primary site of infection.

The complications of Heterophyiasis may include:

• Presence of multiple nodules in lungs that can result in scarring (lung fibrosis); it can be extensive in some cases
• Involvement of the brain or spinal cord: Even though rare, when H. heterophyes infects these tissues, severe neurological complications can occur including epileptic seizures
• Involvement of the heart: Parasitic infection of the heart by H. heterophyes can cause many conditions that may be fatal, if left untreated. These include:
  • Myocarditis (inflammation of the middle layer of the heart wall)
  • Damage to the heart valves
  • Heart failure

How is Heterophyiasis Treated?

Heterophyiasis is typically treated with anti-parasitic medications, such as praziquantel, with dosage and duration as decided by a healthcare provider.

How can Heterophyiasis be Prevented?

The following measures may help prevent Heterophyiasis:

• Avoiding consumption of raw or undercooked fish, especially in the endemic regions. Ensure that fish is grilled or cooked thoroughly; fried fish is also safe for consumption
• Washing hands and utensils after cooking fish
• Avoiding defecating in water or near waterbodies
• It would be helpful to undertake periodic stool examinations for individuals in professions such as fishing
• Seeking immediate medical attention for infections and following it up with prompt treatments
• Controlling the populations of snails in the endemic regions, to limit the development of H. heterophyes larvae and prevent infection spread

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

The prognosis of Heterophyiasis is generally positive with appropriate treatment. The possible outcomes of Heterophyiasis include:

• With suitable treatment, Heterophyiasis can be cured completely
• Without treatment, Heterophyiasis can result in severe complications if the organism enters the blood or lymph and travels to other organs in the body. In rare occasions, this migration can cause fatal complications

Additional and Relevant Useful Information for Heterophyiasis:

• A mature adult H. heterophyes can measure 1 to 1.7 mm long and 0.3 to 0.4 mm wide. Its body is covered by scales
• Eggs can appear in the feces of an infected host 2 to 5 weeks after the host is infected
• Though H. heterophyes infect humans, other mammals, such as dogs and cats, are more commonly infected