Protozoa are a type of parasite. They make up a diverse group of microscopic, one-celled organisms. Some protozoa need a human or animal host to live. Others are called "free-living amebas" because even though they are parasites they live in soil or water and do not need a human or animal host (see Introduction to Free-Living Amebas).
Insects that carry and transmit parasites that cause diseases in people are called vectors. For example, infected female mosquitoes are vectors that transmit the parasites that cause malaria, and infected tsetse flies are the vectors that transmit the parasites that cause African sleeping sickness.
Protozoa can cause infections in various organs of the human host's body, but extraintestinal protozoa are so-called because they cause infections only in areas outside of the intestines such as the blood, liver, lungs, brain, skin, and the tissues beneath the skin. These infections cause various symptoms and complications.
Extraintestinal protozoa infections include the following:
(See also Overview of Parasitic Infections.)
