Parasites
Parasites are organisms that live on or in a host organism and get their food from or at the expense of their host. There are three main classes of parasites that can cause disease in humans: protozoa, helminths, and ectoparasites.
Protozoa[edit | edit source]
Protozoa are microscopic, one-celled organisms that can be free-living or parasitic in nature. They are able to multiply in humans, which contributes to their survival and also permits serious infections to develop from just a single organism. Transmission of protozoa that live in a human's intestine to another individual typically occurs through a fecal-oral route (for example, contaminated food or water or person-to-person contact). Protozoa that live in the blood or tissue of humans are transmitted to other humans by an arthropod vector (for example, through the bite of a mosquito or sand fly).
Helminths[edit | edit source]
Helminths are large, multicellular organisms that are generally visible to the naked eye in their adult stages. Like protozoa, helminths can be either free-living or parasitic in nature. In their adult form, helminths cannot multiply in humans. There are three main groups of helminths (derived from the Greek word for worms): flatworms, thorny-headed worms, and roundworms. The helminths include the platyhelminths (or flatworms, which are divided into the cestodes (or tapeworms) and the trematodes (or flukes)) and the nematodes (or roundworms).
Ectoparasites[edit | edit source]
Ectoparasites are organisms that live on the skin of a host, from which they derive their sustenance. This group includes ticks, mites, lice, and fleas.
See also[edit | edit source]
References[edit | edit source]
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