Cryptosporidium and Giardia in commercial and non-commercial oysters (Crassostrea gigas) and water from the Oosterschelde, The Netherlands.

The intestinal parasites Cryptosporidium and Giardia cause gastro-enteritis in humans and can be transmitted via contaminated water. Oysters are filter feeders that have been demonstrated to accumulate pathogens such as Salmonella, Vibrio, norovirus and Cryptosporidium from contaminated water and cause foodborne infections. Oysters are economically important shellfish that are generally consumed raw. Commercial and non-commercial oysters (Crassostrea gigas) and oyster culture water from the Oosterschelde, The Netherlands, were examined for the presence of Cryptosporidium oocysts and Giardia cysts. Nine of 133 (6.7%) oysters from two non-commercial harvesting sites contained Cryptosporidium, Giardia or both. Six of 46 (13.0%) commercial oysters harboured Cryptosporidium or Giardia in their intestines. Data on the viability of (oo)cysts recovered from Oosterschelde oysters were not obtained, however viable (oo)cysts were detected in surface waters that enter the Oosterschelde oyster harvesting areas. The detection of Cryptosporidium and Giardia in oysters destined for human consumption has implications for public health only when human pathogenic (oo)cysts that have preserved infectivity during their stay in a marine environment are present. Our data suggest that consumption of raw oysters from the Oosterschelde may occasionally lead to cases of gastro-intestinal illness.

Calicivirus inactivation by nonionizing (253.7-nanometer-wavelength [UV]) and ionizing (gamma) radiation.

Noroviruses (previously Norwalk-like viruses) are the most common viral agents associated with food- and waterborne outbreaks of gastroenteritis. In the absence of culture methods for noroviruses, animal caliciviruses were used as model viruses to study inactivation by nonionizing (253.7-nm-wavelength [UV]) and ionizing (gamma) radiation. Here, we studied the respiratory feline calicivirus (FeCV) and the presumed enteric canine calicivirus (CaCV) and compared them with the well-studied bacteriophage MS2. When UV irradiation was used, a 3-log(10) reduction was observed at a fluence of 120 J/m(2) in the FeCV suspension and at a fluence of 200 J/m(2) for CaCV; for the more resistant phage MS2 there was a 3-log(10) reduction at a fluence of 650 J/m(2). Few or no differences were observed between levels of UV inactivation in high- and low-protein-content virus stocks. In contrast, ionizing radiation could readily inactivate MS2 in water, and there was a 3-log(10) reduction at a dose of 100 Gy, although this did not occur when the phage was diluted in high-protein-content stocks of CaCV or FeCV. The low-protein-content stocks showed 3-log(10) reductions at a dose of 500 Gy for FeCV and at a dose of 300 for CaCV. The inactivation rates for both caliciviruses with ionizing and nonionizing radiation were comparable but different from the inactivation rates for MS2. Although most FeCV and CaCV characteristics, such as overall particle and genome size and structure, are similar, the capsid sequences differ significantly, making it difficult to predict human norovirus inactivation. Adequate management of UV and gamma radiation processes for virus inactivation should limit public health risks.