Determination of the Recovery Efficiency of Cryptosporidium Oocysts and Giardia Cysts from Seeded Bivalve Mollusks

National Institute for Public Health and the Environment, Laboratory for Zoonoses and Environmental Microbiology, P.O. Box 1, 3720 BA Bilthoven, The Netherlands. .
Journal of food protection (Impact Factor: 1.85). 01/2013; 76(1):93-8. DOI: 10.4315/0362-028X.JFP-12-326
Source: PubMed


The intestinal parasites Cryptosporidium and Giardia are transmitted by water and food and cause human gastroenteritis. Filter-feeding bivalve mollusks, such as oysters and mussels, filter large volumes of water and thus concentrate such pathogens, which makes these bivalves potential vectors of disease. To assess the risk of infection from consumption of contaminated bivalves, parasite numbers and parasite recovery data are required. A modified immunomagnetic separation (IMS) procedure was used to determine Cryptosporidium oocyst and Giardia cyst numbers in individually homogenized oysters (Crassostrea gigas) and mussels (Mytilus edulis). About 12% of the commercial bivalves were positive, with low (oo)cyst numbers per specimen. The recovery efficiency of the IMS procedure was systematically evaluated. Experiments included seeding of homogenized bivalves and whole animals with 100 to 1,000 (oo)cysts. Both seeding procedures yielded highly variable recovery rates. Median Cryptosporidium recoveries were 7.9 to 21% in oysters and 62% in mussels. Median Giardia recoveries were 10 to 25% in oysters and 110% in mussels. Giardia recovery was significantly higher than Cryptosporidium recovery. (Oo)cysts were less efficiently recovered from seeded whole animals than from seeded homogenates, with median Cryptosporidium recoveries of 5.3% in oysters and 45% in mussels and median Giardia recoveries of 4.0% in oysters and 82% in mussels. Both bivalve homogenate seeding and whole animal seeding yielded higher (oo)cyst recovery in mussels than in oysters, likely because of the presence of less shellfish tissue in IMS when analyzing the smaller mussels compared with the larger oysters, resulting in more efficient (oo)cyst extraction. The data generated in this study may be used in the quantitative assessment of the risk of infection with Cryptosporidium or Giardia associated with the consumption of raw bivalve mollusks. This information may be used for making risk management decisions.

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    • "The majority of studies of either freshwater or marine bivalves have concentrated only on Cryptosporidium detection (Palos Ladeiro et al., 2013; Willis et al., 2013), rarely on Giardia (Graczyk et al., 1999) or on both the previous mentioned protozoan parasites or combined with human-infectious microsporidia (Graczyk et al., 2004, 2008; Lucy et al., 2008; Schets et al., 2013). Therefore, in these investigations usually one (mainly IFA test) or different combinations of two or three specific diagnostic methods (i.e. "
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