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Cyclospora and Related Parasitic Protozoa: Detection and Viability Assessment


Parasitic protozoa such as Cyclospora cayetanensis, Cryptosporidium parvum and Microsporidium spp. have emerged as important human pathogens and are closely associated with food and waterborne illness. This project will pursue three (3) aspects of research as they relate to food safety: continued development of sensitive detection methods and better sampling of food and water sources; in vitro cultivation and animal modeling development and risk evaluation; intervention strategies.

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Within the last several years, the protozoan parasites Cyclospora cayetanensis, Cryptosporidium parvum and Microsporidium spp. have become increasingly recognized as important, rapidly emerging human pathogens in immunocompromised and immunocompetent individuals alike. Outbreaks of enteric infections caused by these microorganisms have been associated with food- and waterborne contamination. <P> Since the spring and early summer of 1996, major outbreaks in North America attributed to Cyclospora cayetanensis have been epidemiologically-linked to the consumption of spring crop raspberries from Guatemala. Smaller outbreaks of cyclosporiasis in the United States during the 1990s have been associated with the consumption of other fresh produce-mesclun lettuce and basil. Unpasturized apple cider has been a source for Cryptosporidum parvum infections; scallions have also been implicated. Contaminated water sources are also suspected as a major route in the transmission of all three parasitic protozoa. <P>The difficulties in assessing and controlling possible foodborne contamination and infections with these coccidia are many. There is a general lack of knowledge concerning life cycles (Cyclospora cayetanensis, Microsporidia spp), animal vectors and/or reservoirs, biochemistry,and the inability to efficiently culture the parasite either in an animal model (Cyclospora cayetanensis) or a tissue culture-based system (Cyclospora cayetanensis and Cryptosporidium parvum). An inadequate supply of Cyclospora cayetanensis also contributes to our general lack of understanding. <P>Neither a means for assessing their pathogenicity and survival after exposure to potential intervention treatments nor sufficient infectious dose information is available. Current methods to detect foodborne contamination lack the necessary sensitivity and reliability.<P> In this 3-yr plan, improved sampling and detection methods will be pursued to include fast, reliable, and highly sensitive PCR methodologies that can be applied to a variety of food and water sources. The development of systems for evaluating intervention strategies will include in vitro cultivation of oocysts and identification of model hosts. Development of animal models that mimic human illness caused by these protozoa will be attempted and dose-response studies in normal and immunocompromised animals will then be conducted to provide data for developing risk assessment models. Alternate protozoa such as Eimeria spp. will also be evaluated as research models in the absence of adequate supplies of Cyclospora cayetanensis.
The results of this project will provide for an improved ability to detect and reduce the risk of food and water-borne illness attributed to parasitic protozoa.</P>

Orlandi, Palmer
DHHS/FDA - Center for Food Safety & Applied Nutrition
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