What is Paragonimus?

Paragonimus is a parasitic lung fluke (flat worm). Cases of illness from infection occur after a person eats raw or undercooked infected crab or crayfish. The illness is known as paragonimiasis. Paragonimus infection also can be very serious if the fluke travels to the central nervous system, where it can cause symptoms of meningitis.

Where is Paragonimus found?

Paragonimus westermani and several other species are found throughout eastern, southwestern, and southeast Asia; (including China, the Philippines, Japan, Vietnam, South Korea, Taiwan, and Thailand). P. africanus is found in Africa, and P. mexicanus in Central and South America. There are several species of Paragonimus in other parts of the world that can infect humans. P. kellicotti is found in the midwestern and southern United States living in crayfish. Some human cases of infection have been associated with eating raw crayfish on river raft trips in the Midwest. Paragonimus has caused illness after ingestion of raw freshwater crabs.

How is Paragonimus transmitted?

The infection is transmitted by eating infected crab or crawfish that is either, raw, partially cooked, pickled, or salted. The larval stages of the parasite are released when the crab or crawfish is digested. They then migrate within the body, most often ending up in the lungs. In 6-10 weeks the larvae mature into adult flukes.

What are the signs and symptoms?

Adult flukes living in the lung cause lung disease. After 2-15 days, the initial signs and symptoms may be diarrhea and abdominal pain. This may be followed several days later by fever, chest pain, and fatigue. The symptoms may also include a dry cough initially, which later often becomes productive with rusty-colored or blood-tinged sputum on exertion. The symptoms of paragonimiasis can be similar to those of tuberculosis.

How is Paragonimus infection diagnosed?

The diagnosis is usually made by identifying Paragonimus eggs in the sputum or sometimes in the stool (from ingesting eggs after coughing them up, then passing the eggs in the stool).

Is Paragonimus infection contagious?

No. Paragonimus infection is not contagious.

Is there treatment?

Yes, there is treatment. Once the diagnosis is made, effective treatment for paragonimiasis is available from a physician.

How can I prevent Paragonimus infection?

Never eat raw freshwater crabs or crayfish. Cook crabs and crayfish to at least 145°F (~63°C). Travelers should be advised to avoid traditional meals containing undercooked freshwater crustaceans.

Several species of Paragonimus cause most infections; the most important is P. westermani, which occurs primarily in Asia including China, the Philippines, Japan, Vietnam, South Korea, Taiwan, and Thailand. P. africanus causes infection in Africa, and P. mexicanus in Central and South America. Specialty dishes in which shellfish are consumed raw or prepared only in vinegar, brine, or wine without cooking play a key role in the transmission of paragonimiasis. Raw crabs or crayfish are also used in traditional medicine practices in Korea, Japan, and some parts of Africa.

Although rare, human paragonimiasis from P. kellicotti has been acquired in the United States, with multiple cases from the Midwest. Several cases have been associated with ingestion of uncooked crawfish during river raft float trips in Missouri.

Infection with Paragonimus spp. can result in an acute syndrome with cough, abdominal pain, discomfort, and low-grade fever that may occur 2 to 15 days after infection. Persons with light infections may have no symptoms. Symptoms of long-term infection may mimic bronchitis or tuberculosis, with coughing up of blood-tinged sputum.

The infection is usually diagnosed by identification of Paragonimus eggs in sputum. The eggs are sometimes found in stool samples (coughed-up eggs are swallowed). A tissue biopsy is sometimes performed to look for eggs in a tissue specimen.

Specific and sensitive antibody tests based on P. westermani antigens are available through CDC, and serologic tests using a variety of techniques are available through commercial laboratories.

Paragonimus infections are treatable by your health care provider. Prescription medications are available.

Never eat raw freshwater crabs or crayfish. Cook crabs and crayfish for to at least 145°F (~63°C). Travelers should be advised to avoid traditional meals containing undercooked freshwater crustaceans.