Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 17, 1997
Publication Date: N/A
Interpretive Summary: Cryptosporidium is a protozoan pathogen of humans and animals that is both foodborne and waterborne. As freshwater flows to estuarine environments, such as the major rivers draining farmlands in Pennsylvania, Maryland, and Virginia and emptying into the Chesapeake Bay, so are pathogens such as Vibrio and Cryptosporidium carried. In the present study oysters from the Chesapeake Bay were shown to remove oocysts in an artificial seawater aquarium and hold them in gills, gut contents and blood cells for a month after exposure. This is the first report showing that oysters can filter out and harbor C. parvum oocysts and it suggests that eating such oysters could result in foodborne infection.
Cultured Eastern oysters, from natural waters in the Chesapeake Bay were placed in each of 2 aquaria containing artificial seawater. Algae were added 3X weekly but oysters were otherwise undisturbed except when sample specimens were collected. At time 0, oocysts of Cryptosporidium parvum strain AUCP-1, purified from bovine feces, were added to one aquarium. Aliquots of seawater removed at intervals from 1 to 168 hr later revealed a sequential reduction from 300 to 0 oocysts/ml by 24 hr. Gill washings and hemolymph were aspirated from 30 oysters at 3, 24, 168 (1 wk), and 720 hr (1 mo) after oocysts were added and a small quantity from each specimen was air-dried on 2 glass microscope slides. Tissues from 20 oysters were fixed at the 24, 168, and 720 hr intervals and 2 tissue sections from each oyster were prepared for histology. Gill washings, hemolymph preparations and histologic specimens were also obtained from control oysters in the aquarium that did not receive oocysts. One set of specimens were stained with acid-fast stain and examined by brightfield microscopy, the other set was stained with fluorescein labelled anti-Cryptosporidium monoclonal antibody and examined by fluorescence microscopy. Immunofluorescence microscopy provided greater sensitivity and ease of oocyst identification. Oocysts were found in gill washings, within hemolymph cells, and in the stomach-intestine of some oysters at all time periods examined, indicating that they were filtered from the water, entered the body, and were retained from 3 hr to 1 mo after initial exposure.