Cryptosporidium parvum: an emerging parasite in foods.

Cryptosporidium parvum is a parasite linked to significant public health problems in the water industry and is now emerging as a potential food contaminant. C. parvum is a parasite found in the intestinal tract of animals, including cattle and sheep and is excreted in the feces of infected animals and humans. The parasite can be transmitted from animal-to-person, person-to-person, through ingestion of fecally contaminated water or food, or by direct contact with contaminated environmental surfaces.

The clinical symptoms of C. parvum infection include acute watery diarrhea with abdominal pain, accompanied by nausea, vomiting, weight loss and low-grade fever. The disease is usually self-limiting, with a duration of two to three weeks, but in the immunocompromised, including children and the elderly, the illness can become chronic and persistent and may result in the death of the infected individual.

While predominantly considered a waterborne contaminant, C. parvum has also been linked to a small number of foodborne outbreaks involving raw goat's milk, tripe, salad, raw milk, offal, sausage and apple cider. To date, the sources of many C. parvum infections have never been identified due to a lack of routine methods for the detection of this pathogen. There is sparse data available on the risk the parasite poses in foods.

Recognizing the importance of this emerging organism and the need for more information on the risks that it poses, the European Union in 2000 funded a three-year program to generate information on C. parvum in food. The project was coordinated by The National Food Center, Dublin, Ireland, and involved a team of eight European research groups.

Scientists have developed methods to detect Cryptosporidium on food samples, including beef and salad crops, using techniques based on a pulsifier machine (Microgen Bioproducts Ltd., Camberley, U.K.) for isolating the oocysts from food. They also developed immunofluorescent microscopy to detect the oocysts and DNA analysis to characterize and type the oocysts.

The techniques have been used in studies to determine the prevalence of the parasite and to establish how well it persists if it gets onto foods. Studies conducted in beef abattoirs looked for the parasite in feces of animals coming in for slaughter, in water used to wash carcasses and on beef carcasses. Cryptosporidium spp. was isolated from 20 of 288 (6.9%) fecal samples. The parasite was also detected in 10 of 46 water samples in an abattoir that sourced water from a river. Cryptosporidium was not detected in water sourced from bore holes and the parasite was not detected on any of the 288 carcass meat samples examined.

Studies were also undertaken to see how well Cryptosporidium would survive on meat, which was frozen. The results showed an approximate reduction of 92% in the numbers of parasite on beef trimmings following a freeze-thaw process. Cooking meat will inactivate Cryptosporidium.

In animal slurries collected from a small number of farms, 11% of the samples contained C. parvum. Studies on the survival of oocysts in slurries demonstrated that at 4 C, a high percentage (50% to 70%) of oocysts remained viable regardless of pH value (4, 7 and 9) after 100 days of storage.

Surveillance of salad crops for occurrence of Cryptosporidium was also undertaken. On lettuce collected straight from the fields, the percentage of positive samples on different farms ranged from 16% to 30%. No Cryptosporidium was found on lettuce for sale in stores.

The results from the research indicate that Cryptosporidium is present in the food environment. Although it was not detected on food for sale, it highlights that Good Manufacturing Practices (GMP) and Hazard Analysis Critical Control (HACCP) systems are needed to prevent the parasite from contaminating the food supply. Increased surveillance and monitoring of the food supply for parasites such as Cryptosporidium is needed.

Further information. Dr. Geraldine Duffy, Teagasc, The National Food Center, Ashtown, Dublin 15, Ireland; phone: + 353-1-8059500; fax: + 353-1-8059550; email: [e-mail].