Six residents of Missouri and Illinois came down with a rare parasitic disease — paragonimiasis – caused by Paragonimus trematodes, or lung flukes, between September 2009 and September 2010, according to the Centers for Disease Control and Prevention.


In North America, infection by lung flukes isn’t all that unusual in dogs, cats or wild carnivores, but it is rarely seen in humans, who can get it from eating raw or undercooked crayfish or freshwater crabs that harbor the worn-like parasites, the CDC said in its most recent Weekly Morbidity and Mortality Report.

Worldwide, however, paragonimiasis sickens about 22 million, particularly in East Asia.

As foodborne illnesses go, it’s pretty high up on the “yuck” scale.  After the trematode is ingested, the parasite can penetrate the intestinal wall and then the abdomen and diaphragm to enter the lungs.  In severe cases it migrates to other organs and the brain, and can cause serious problems, like blindness.

The six most recently infected individuals in the United States are in addition to three other confirmed cases in Missouri since 2006.  All nine victims, who ranged in age from 10 to 32, had eaten raw or undercooked crayfish from Missouri rivers while they were canoeing or camping.

 “Behavioral factors” were at work in the victims’ choice of seafood, the CDC said.  Seven of the adults had been drinking and two ate the crayfish on a dare. The child, on a camping trip, was showing off outdoor survival skills.

Onset of their illnesses ranged from 2 to 16 weeks after they ate the infected crayfish.

All suffered from diarrhea, abdominal pain, fever, cough, and pleural effusion (excess fluid in the lungs), the CDC said.  Some of their doctors had difficulty diagnosing their problem.  One patient who was initially misdiagnosed underwent gallbladder removal, although after the surgery the gallbladder was found to be normal.  Another person was given multiple diagnostic tests and failed treatments before the illness was correctly identified.

After the patients were treated with praziquantel, a drug used to expel parasitic worms, their symptoms promptly improved.  They all recovered within 1−3 months of treatment, the CDC said.


Paragonimiasis is not required to be reported to health authorities, but in April this year the Missouri Department of Health and Senior Services issued an advisory, trying to raise physicians’ awareness of the illness and its symptoms, and asked health providers to voluntarily report any cases.  MDHSS also put together an investigation form and revised the Missouri Health Surveillance Information System for reporting it.

Health-care providers, the CDC recommended, should consider paragonimiasis when patients show up with unexplained fever, cough, eosinophilia (a blood condition indicative of a parasite), and pleural effusion or other chest x-ray abnormalities.  They should ask these people if, by chance, they’ve recently eaten raw or undercooked crayfish.

And the U.S. Food and Drug Administration advises cooking shellfish to an internal temperature of 145 degrees to help ensure its safety.