Define "parasite."

In many food safety education programs, the term "parasite" actually refers to protozoa. Protozoa are unicellular and microscopic. They are notable for their ability to move independently. Most protozoal species are aerobic, but some anaerobic species have been found in the human intestine and animal rumen.

Protozoa are located in most moist habitats. Free-living species inhabit freshwater and marine environments, and terrestrial species inhabit decaying organic matter. Some species are "parasites" of plants and animals.

Protozoa vary substantially in size and shape. Smaller species may be the size of fungal cells; large species may be visible to the unaided eye. Many protozoa alternate between a free-living vegetative form known as a trophozoite and a resting form called a cyst. The protozoal cyst is somewhat similar to the bacterial spore, because it resists harsh conditions in the environment. Many protozoal parasites are taken into the body in the cyst form.

Protozoa that are associated with foodborne illness include: Trichinella spiralis, Cryptosporodium spp., Cyclospora spp, Giardia lamblia, and Anisakis, etc. For more information about these protozoa go to the FDA Bad Bug Book available at: www.cfsan.fda.gov/~mow/intro.html