Optimizing methods for detection of Cryptosporidium oocysts in nativeoysters from the Chesapeake Bay

摘要

Several groups have documented the presence of Cryptosporidium, an anthropozoonotic enteric parasite, in oysters harvested for commercial purposes. Getting accurate estimates of Cryptosporidium contamination levels in oysters is difficult because recovery efficiencies are dependent on the isolation method used. Such estimates are important for determining the human health risks posed by consumption of contaminated oysters in a raw form. In this study, recovery efficiencies are compared for multiple methods used to isolate Cryptosporidium oocysts from experimentally contaminated oysters. Oysters were harvested after being allowed to filter oocysts from spiked aquarium water for approximately 24 hours. In one group, the entire oyster meat and all hemolymph was processed by diethyl ether extraction followed by immunomagnetic separation (IMS) of oocysts from the resulting pellet. In another group, the oysters were dissected so that only gills, digestive diverticula and hemolymph were processed as described above. In the last group, oocysts were isolated directly from hemolymph alone by IMS. Recovered oocysts were enumerated by IFA. Recovery efficiencies for the methods described above were also determined using oyster tissue homogenate and hemolymph spiked with 1000 oocysts, to control for differences in recoveries related to differences in oocyst uptake rates among oysters. The results from this study will be used to determine the best method for quantifying Cryptosporidium levels in oysters collected from the Chesapeake Bay. This method would have broad application to native and non-native commercially harvested oysters and would be beneficial for regulatory agencies charged with determining safety of shellfish for human consumption.