Structure: Protozoa

Protozoa are single-celled organisms that feed by scavenging for particles and other microorganisms, such as bacteria, or by absorbing nutrients from their environment. Many types of protozoa live in moist places, such as soil, water, or sewage, and some of these may infect humans and other animals, causing disease. Other types of disease-causing protozoa depend on bloodsucking insects, such as mosquitoes, to spread them among human hosts. Most cases of protozoal infection occur in the tropical regions of the world.

Infected cell

The crescent-shaped protozoa seen at right are leaving an infected body cell. This particular protozoan causes the disease toxoplasmosis.

From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.

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