Cryptosporidium and Giardia in commercial and non-commercial oysters (Crassostrea gigas) and water from the Oosterschelde, the Netherlands Franciska M. Schets ⁎ , Harold H.J.L. van den Berg, George B. Engels, Willemijn J. Lodder, Ana Maria de Roda Husman National Institute for Public Health and the Environment, Microbiological Laboratory for Health Protection, P.O. Box 1, 3720 BA Bilthoven, The Netherlands Received 2 December 2005; received in revised form 16 February 2006; accepted 13 June 2006 Abstract 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. © 2006 Elsevier B.V. All rights reserved. Keywords: Cryptosporidium; Giardia; Shellfish; Oysters; Water; Detection 1. Introduction The intestinal parasites Cryptosporidium and Giardia cause gastro-enteritis in humans. Giardia infections are usually self- limiting with clearance within two to four weeks. They may be asymptomatic and chronic infections do occur, but when diag- nosed, Giardia infections can be effectively treated (Marshall et al., 1997). In otherwise healthy individuals, symptoms of Cryptosporidium infections generally persist for one to two weeks but in immunocompromised persons infections can be chronic with diarrhoea being severe and life threatening (Arrowood, 1997). Waterborne transmission of Cryptosporidium oocysts and Giardia cysts is associated with consumption of contaminated drinking water and recreation in contaminated surface water or swimming pools (Fayer et al., 2000; Thompson, 2004). Many water related outbreaks of cryptosporidiosis have been reported over the past years (Fayer, 2004; Fayer et al., 2004). Foodborne infections have been reported as the result of consumption of contaminated school milk (Gelletlie et al., 1997), fresh-pressed apple cider (Millard et al., 1994) and chicken salad (Besser- Wiek et al., 1996), whilst a survey in Norway demonstrated the presence of Cryptosporidium and Giardia on commercially available fruits and vegetables (Robertson and Gjerde, 2001). Bivalve shellfish are filter feeders that filter large volumes of seawater from which particles are extracted and concentrated. In the case of either human or animal faecal contamination of the seawater, waterborne pathogenic bacteria, viruses or protozoa like Cryptosporidium or Giardia are accumulated in the shellfish tissues. Raw consumption of these contaminated shellfish, which is preferred, can make them vectors of disease. Salmonella, Shigella, hepatitis A virus, norovirus and Vibrio have been frequently detected in shellfish and are known causes of many foodborne infections worldwide (Potasman et al., 2002). Consumption of raw oysters was linked to outbreaks of International Journal of Food Microbiology 113 (2007) 189 – 194 www.elsevier.com/locate/ijfoodmicro ⁎ Corresponding author. Fax: +31 30 2744434. E-mail address: ciska.schets@rivm.nl (F.M. Schets). 0168-1605/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.ijfoodmicro.2006.06.031