(KMOV) -- Anyone planning to spend time at the river this summer should not eat raw crayfish.
They can carry a rare parasitic worm that can cause extreme sickness.
To date, Missouri has had six cases of people infected with the worm, and that brings the North America total to 13.
One of the six victims was a Florissant teenager who ate a crayfish on a float trip as a joke. For months, doctors couldn't figure out what was wrong with him.
Doctors at the Washington University School of Medicine say of the six infections they've seen over the past year, all of the patients ate raw crayfish from Missouri streams.
If left untreated, doctors say the worm can travel into the lungs and the brain. However, it is easily treatable if detected in time.
The parasite lives in the heart of a crayfish.
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