Testing for food-borne parasites, their metabolic products and symbionts.

Microscopic animals associated with foods include free-living and saprophytic invertebrates, parasites of hosts other than humans, and parasitic animals specifically designated as food-borne that can infect a human host by the gastrointestinal route. The first general method used to screen for food-borne species was digestion with pepsin and hydrochloric acid at 36 degrees C, based on the "artificial stomach juice" technique for recovering larvae of the nematode Trichinella spiralis from muscle. This method selects for forms capable of surviving a mammalian digestive enzyme at mammalian temperatures. It has been used successfully to recover a variety of food-borne helminths, not only from mammalian flesh but also from fish, shellfish and molluscs, and can be adapted to greatly reduce the "background of living animals" associated with soils and the crops grown in them. However, not all animal forms that survive digestion are food-borne parasites, and all that succumb are not necessarily noninfectious. Methodology to test for food-borne parasites is, in general, not as efficient as that for food-borne bacteria. Recent developments in food parasitology indicate a need to identify not only the parasite, but also its metabolic products and associated symbionts.