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Paragonimiasis is an infection with parasitic worms. It is caused by eating undercooked crab or crayfish.

Usually there are no symptoms. But paragonimiasis can cause illness resembling pneumonia or stomach flu. It can last for years.

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Paragonimiasis Causes

Paragonimiasis is caused by infection with a trematode. That's a parasitic worm also called a fluke or lung fluke because it commonly infects the lungs. Usually, infection comes after eating undercooked crab or crayfish that carry immature flukes.

Once swallowed by a person, the worms mature and grow inside the body. Over months, the worms spread through the intestines and belly (abdomen). They penetrate the diaphragm muscle to enter the lungs. Once inside the lungs, the worms lay eggs and can survive for years, causing chronic (long-term) paragonimiasis.

Paragonimiasis is rare in the U.S. Most cases occur in Asia, West Africa, and South and Central America.

Paragonimiasis Symptoms

Paragonimiasis causes no symptoms during initial infection. Many people with paragonimiasis never experience any symptoms. When paragonimiasis symptoms do occur, they result from the worms’ location and activity in the body, which change over time.

In the first month or so after someone is infected, paragonimiasis worms spread through the abdomen, sometimes causing symptoms that can include:

Worms then travel from the belly into the chest. There they can cause respiratory symptoms, such as:

Without treatment, paragonimiasis becomes chronic. It can continue for decades.

The most common long-term paragonimiasis symptom is a cough with bloody sputum (hemoptysis) that comes and goes. Other chronic paragonimiasis symptoms may include:

  • Belly pain
  • Nausea
  • Vomiting
  • Bloody diarrhea
  • Lumps or bumps on the skin of the belly or legs that come and go over time

Some people with chronic paragonimiasis have no noticeable symptoms.

In less than 1% of people with paragonimiasis, the worms infect the brain. Symptoms can include:

Paragonimiasis Diagnosis

Diagnosing paragonimiasis can be difficult or delayed. That's because its symptoms are often mild and overlap with more common conditions.

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