August 30, 1999
Parasites Found in Chesapeake Bay
Oysters Can Cause Illness
ATLANTA, GA (SafetyAlerts)
- Cryptosporidium, a parasite that causes diarrhea, can be added to the list of
reasons not to eat raw oysters, according to an article in an upcoming issue of CDC's Emerging
Infectious Diseases journal.
Researchers tested oysters from seven sites used
for commercial harvesting in the Chesapeake Bay area. Oysters from all the sites contained
Cryptosporidium species both from cows and people. This finding shows that the
water at these sites contained human and animal feces during a period when the oysters
were filtering. The risk of contamination is probably higher after a heavy rain, but some
risk is present year-round.
Oysters feed by filtering water through their
gills. When water is contaminated by run-off from pastures or sewage, oysters can keep the
parasite in their gills and spread illness.
Infection with Cryptosporidiumm can cause
prolonged diarrhea. The infection is especially dangerous for persons with weakened immune
systems. However, heating to temperatures above 162° F kills the parasite, so the authors
urge that oysters be cooked before they're eaten.
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