Submitted to: Emerging Infectious Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/2/1999
Publication Date: N/A
Interpretive Summary: Cryptosporidiosis is a waterborne pathogen affecting the health of humans and livestock. The oocyst stage excreted in the feces of infected humans and animals can survive in the environment for months. Earlier studies by ARS scientists demonstrated that shellfish such as oysters, clams and mussels can remove oocysts from artificially contaminated water and that some shellfish in areas of sewage outfalls and rivers draining animal agricultural lands can be found to harbor oocysts. The present study examined oysters from commercial bars in the Chesapeake Bay, where oysters are harvested for human consumption. Two genetic types of Cryptosporidium parvum were found, a human genotype transmitted only from humans to humans, and a bovine genotype transmitted amongst a variety of animals and humans. These findings confirm fecal contamination by both animals and humans of Bay waters and shellfish at all oyster bars sampled, indicating widespread fecal contamination of surface waters and the need to thoroughly cook shellfish to prevent infection by fecal borne pathogens.
Technical Abstract: Cryptosporidium parvum, a zoonotic waterborne pathogen, is prevalent and widely distributed in surface waters of North America. Recent laboratory and field studies demonstrated that bivalve molluscs could remove C. parvum oocysts from contaminated water and retain them on gills and in hemolymph. To our knowledge oysters from bars used for commercial harvesting have never been examined for oocysts. In the present study oysters were collected in the autumn of 1997, winter of 1998,and autumn of 1998 by the Maryland Department of Natural Resources from six oyster bars open to commercial harvesting. Gill washings and hemolymph were examined for the presence of C. parvum oocysts by immunofluoresence microscopy, polymerase chain reaction (18s rDNA and Cp11), gene sequencing (18s rDNA), and mouse bioassay. Oocysts of the bovine genotype of C. parvum (genotype 2) were identified in specimens from every site. Those of the human genotype (genotype 1) were repeatedly found at one site. These findings document the presence of C.parvum infectious for humans in oysters intended for human consumption and serve to warn that consumption of raw oysters carries the risk of infection with a pathogen for which there is no approved chemotherapy.