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

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

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

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

• Parasitology
• Parasitic disease
• List of parasites of humans

References

Parasites Resources
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