Foodborne Parasites a Review of the Scientific Literature Review
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FRI BRIEFINGS Foodborne Parasites A Review of the Scientific Literature Review M. Ellin Doyle Food Research Institute University of Wisconsin–Madison Madison WI 53706 Contents Parasites34B — What are they? .......................................................................................................2 What foods have the potential for carrying parasites? ............................................................2 How much of a problem are parasites? .....................................................................................3 How can parasites be controlled? ..............................................................................................4 Sanitation and hygiene ..........................................................................................................4 Animal husbandry and inspection .........................................................................................5 Marination, pickling, smoking, fermentation ........................................................................5 Cooking and heat treatment ...................................................................................................5 Freezing .................................................................................................................................6 Filtration and chlorination and other disinfectants ................................................................6 Other physical processes .......................................................................................................6 Life cycle targets ...................................................................................................................6 Life cycles of parasites ................................................................................................................7 Direct reinfection ..................................................................................................................7 Completion of life cycle in one host ......................................................................................7 One intermediate host ............................................................................................................7 Two intermediate hosts .........................................................................................................7 Protozoan parasites .....................................................................................................................7 Toxoplasma ...........................................................................................................................8 Cryptosporidium ...................................................................................................................9 Cyclospora ..........................................................................................................................10 Entamoeba ..........................................................................................................................10 Giardia ................................................................................................................................11 Parasitic worms — Nematodes ................................................................................................12 Anisakis and Pseudoterranova (sealworm, codworm) ........................................................12 Ascaris .................................................................................................................................12 Angiostrongylus cantonensis and A. costaricensis (rat lungworm) .....................................13 Gnathostoma sp. ..................................................................................................................13 Trichinella spiralis (trichinosis) ..........................................................................................13 Parasitic worms — Trematodes ...............................................................................................14 Clonorchis/Opisthorchis (liver flukes) ................................................................................14 Fasciola hepatica (liver fluke) ............................................................................................14 Fasciolopsis buski (fasciolopsiasis, intestinal fluke) ...........................................................15 Paragonimus (lung fluke) ...................................................................................................15 Parasitic worms — Cestodes ....................................................................................................15 Taenia spp. ..........................................................................................................................15 Diphyllobothrium spp. (fish tapeworm) ..............................................................................16 Echinococcus spp. ...............................................................................................................16 Summary ....................................................................................................................................17 References ..................................................................................................................................18 Appendix — FRI Briefing, November 1996: Cryptospordium and Cyclospora ... following page 28 34B Prepared by M. Ellin Doyle, Ph.D., [email protected] October 2003 http://fri.wisc.edu/docs/pdf/parasites.pdf Food Research Institute, University of Wisconsin–Madison 2 FRI BRIEFINGS: Foodborne Parasites Parasites — What are they? organisms but are larger and more complex than bacteria. These parasites are generally not susceptible The word "parasites" conjures up images of gross- to antibiotics that kill bacteria but there are effective looking tapeworms, roundworms, and fleas, or of drugs to treat some (not all) parasitic infections. blood-borne diseases such as malaria and schistoso- miasis. Many have been considered problems con- fined to tropical countries and places with poor What foods have the potential for sanitation and therefore of little concern to the U.S. However, recent outbreaks of parasitic diseases have carrying parasites? demonstrated the inaccuracy of these assumptions. Parasites of concern to food safety professionals Not all parasites live only in the tropics [as witness include several worms, ranging from a few centime- the Milwaukee Cryptosporidium outbreak (179)], and ters to several meters in length, and protozoa, single consumers in the U.S. can be exposed to parasites celled organisms (202;212) (Table 1). Many parasitic that originate in the tropics because of increasing infections are asymptomatic, others cause acute short- international travel [Angiostrongylus in tourists re- lived effects, and still others may persist in the body turning from Jamaica (252)] and globalization of food causing chronic effects (195). markets [Cyclospora on raspberries from Guatemala (128)]. Finally, some of the most important parasites Protozoa are neither tapeworms, insects, nor blood-borne. Protozoan parasites may be present in freshwater Parasites are organisms that obtain their food from sources that have been contaminated with human or other living creatures. A “good” or well-adapted para- animal feces; fruits and vegetables grown or washed site does not kill its host because it depends on the with such contaminated water may have parasites on host for a steady supply of food over a long period of their surface and be sources of infection. Toxoplasma time. Usually parasites are smaller than their food is sometimes present in raw meat, particularly pork, source and this distinguishes them from predators and thorough cooking is needed to destroy it. Some such as tigers, which also eat other living things. protozoa are very species specific and can survive in Some parasites live in only one species of animal but only one species of animal, but others, including many parasites, particularly the worms, spend part of many human pathogens, can live in humans and in their lives reproducing sexually in a final or definitive other animals and these animals may act as reservoirs host and developing asexually as larvae during another continually shedding parasites into the environment. part of their life in an intermediate host of a different Protozoan parasites have a resistant resting stage species. Different life cycles will be described in a (cyst or oocyst) which can withstand some drying later section. and disinfectants. It has been estimated that humans harbor about 300 species of parasitic worms and over 70 species Foodborne parasitic worms of protozoa (27;51;212). Many of these have co- Cestodes (tapeworms): Meat and fish may contain existed with us for thousands of years and have been larval tapeworms that can develop into adults in the identified among human remains by archaeologists human intestine. The pork and beef tapeworms are (62;104;116;123;173;213;231). We may have inher- the best known (Taenia solium and T. saginata, ited some parasites from our primate ancestors, while respectively) but there are also other species with others were acquired from companion and food ani- larval stages in fish muscles. Tapeworm eggs may mals. Not all parasites are foodborne and some are be present on fruits or vegetables fertilized with very rare. human wastes or washed with contaminated water. This review will summarize information on the If humans consume the eggs of T. solium,