TWENTY-FOURTH ANNUAL EASTERN FISH HEALTH WORKSHOP Royal Pavilion Resort, Atlantic Beach, NC MARCH 9-11, 1999 Studies Of Cryptosporidium In Oysters From Chesapeake Bay Earl J. Lewis1, Ronald Fayer2, Thaddeus K. Graczyk3, James M. Trout2, and C. Austin Farley1 1National Ocean Service, Center for Coastal Environmental Health and Biomolecular Research, Cooperative Oxford Laboratory, Oxford, MD 21654-9724; 2U.S. Department of Agriculture, Agricultural Research Service, Immunology and Disease Resistance Laboratory, Beltsville, MD 20705-2350; 3Johns Hopkins University, School of Hygiene and Public Health, Department of Molecular Microbiology and Immunology, and Department of Environmental Sciences, Baltimore, MD 21205-2179 Cryptosporidium parvum is a protistan parasite that causes cryptosporidiosis, a severe disease of humans and other mammals. Two genotypes of C. parvum are known: a human adapted genotype (type 1) and an animal adapted genotype (type 2) that infects humans and many other mammals. Cryptosporidiosis is an emerging zoonotic disease worldwide with infections reported from 92 countries. The parasite causes intense diarrhea and infections may be fatal within immunocompromised individuals. Control of the disease is difficult since the organism does not respond to treatment with approved medications and the environmental stage withstands chemical disinfection. In 1997, a study was begun to determine if oysters Crassostrea virginica could serve as an indicator of C. parvum contamination in the estuarine environment. Our earlier experimental studies showed that oysters effectively filtered C. parvum oocysts from artificial seawater and that oocysts were harbored in tissues throughout the oyster. Oocysts in oysters remained viable for at least 1 week. When maintained in artificial seawater, oocysts remained viable for 2 to 8 weeks depending on salinity and temperature. Subsequent field studies at 13 oyster bars in Maryland tributaries of Chesapeake Bay demonstrated that feral oysters from all locations harbored the parasite. Stations chosen for study were selected for proximity to sewage outfalls and cattle farms, or for being the most upriver oyster bar. Both genotypes of C. parvum were found in oysters, although the type 1 isolate was rarely recovered. Results of this study show oysters are a good indicator of environmental contamination by C. parvum and they also raise a public health concern for the harvest and consumption of raw shellfish from waters contaminated with the organism. This study is being funded in part by Maryland Sea Grant, R/F-88. Return to 24th Annual Eastern Fish Health Workshop Return to Leetown Science Center Home Page