Quantitative assessment of viable Cryptosporidium parvum load in commercial oysters (Crassostrea virginica) in the Chesapeake Bay

Thaddeus K. Graczyk, Earl J. Lewis, Gregory Glass, Alexandre J. Dasilva, Leena Tamang, Autumn S. Girouard, Frank C. Curriero

Research output: Contribution to journalArticlepeer-review

29 Scopus citations


The epidemiological importance of increasing reports worldwide on Cryptosporidium contamination of oysters remains unknown in relation to foodborne cryptosporidiosis. Thirty market-size oysters (Crassostrea virginica), collected from each of 53 commercial harvesting sites in Chesapeake Bay, MD, were quantitatively tested in groups of six for Cryptosporidium sp. oocysts by immunofluorescent antibody (IFA). After IFA analysis, the samples were retrospectively retested for viable Cryptosporidium parvum oocysts by combined fluorescent in situ hybridization (FISH) and IFA. The mean cumulative numbers of Cryptosporidium sp. oocysts in six oysters (overall, 42.1±4.1) were significantly higher than in the numbers of viable C. parvum oocysts (overall, 28.0±2.9). Of 265 oyster groups, 221 (83.4%) contained viable C. parvum oocysts, and overall, from 10-32% (mean, 23%) of the total viable oocysts were identified in the hemolymph as distinct from gill washings. The amount of viable C. parvum oocysts was not related to oyster size or to the level of fecal coliforms at the sampling site. This study demonstrated that, although oysters are frequently contaminated with oocysts, the levels of viable oocysts may be too low to cause infection in healthy individuals. FISH assay for identification can be retrospectively applied to properly stored samples.

Original languageEnglish (US)
Pages (from-to)247-253
Number of pages7
JournalParasitology Research
Issue number2
StatePublished - Jan 2007

ASJC Scopus subject areas

  • Parasitology
  • General Veterinary
  • Insect Science
  • Infectious Diseases


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