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United States Department of Agriculture

Agricultural Research Service

Title: Contamination of Atlantic Coast Commercial Shellfish

Authors
item Fayer, Ronald
item Trout, James
item Santin, Monica - VISITING SCIENTIST ARS
item Lewis, Earl - NOAA
item Xiao, L - CDC

Submitted to: Parasitology Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 14, 2002
Publication Date: January 1, 2003
Citation: Fayer, R., Trout, J.M., Santin, M., Lewis, E.J., Xiao, L. 2003. Contamination of Atlantic coast commercial shellfish. Parasitology Research. 89:141-145.

Interpretive Summary: Cryptosporidium is found outside the body in the oocyst stage, excreted in feces from infected humans and animals and acquired by ingestion of contaminated water and food. The environmentally hardy oocyst stage has been detected in oysters in the Chesapeake Bay harvested from sites near sewage outfalls and dairy farms. Shellfish harbor oocysts as a result of exposure to human and animal feces in estuarine and coastal waters, serving as indicators of human and animal fecal pollution of these waters. The present study, of commercial shellfish from 37 sites in 8 states along the Atlantic coast from New Brunswick, Canada to Florida found Cryptosporidium in shellfish from 64.9% of the sites by either microscopy or molecular testing. Previous reports have linked periods of high rainfall with elevated numbers of pathogen contaminated shellfish, a likely result of runoff from fields and pastures. Because shellfish in the present study were examined during a period of exceptionally low precipitation, the data are thought to underestimate the number of Cryptosporidium contaminated shellfish likely to be found during periods of normal or above normal precipitation

Technical Abstract: Shellfish (oysters and/or clams) were obtained from 37 commercial harvesting sites in 12 Atlantic coast states from Maine to Florida and 1 site in New Brunswick, Canada. Gill washings from 25 shellfish at each site were examined by immunofluorescence microscopy (IFA) for oocysts of Cryptosporidium. Gill washings from another 25 shellfish at each site were pooled into 5 pools; DNA from each pool was utilized for PCR and genotyping. Oocysts were found in shellfish from New Brunswick and 11 of 13 states, in 3.7% of 925 oysters and clams examined by immunofluorescence microscopy. Cryptosporidium DNA was detected by PCR in 35.2% of 185 pools. Cryptosporidium parvum genotype 1 and 2, and C. meleagridis, all previously found in infected humans, were identified at 37.8% of the sites. Gill washings from every site were tested by biological assay in mice but no mice were found infected, suggesting that oocysts were no longer infectious or infections in mice were below the level of detection. Collectively these findings indicate that Cryptosporidium species, indicative of pollution from human and animal feces and potentially infectious for humans, were found in commercial shellfish from 64.9% of sites examined along the Atlantic coast by either microscopy or molecular testing. Previous reports link periods of high rainfall with the elevated numbers of pathogen contaminated shellfish. Because shellfish in the present study were examined during a period of exceptionally low precipitation, the data are thought to underestimate the number of Cryptosporidium contaminated shellfish likely to be found during periods of normal or above normal precipitation.

Last Modified: 10/22/2014