Tuesday, April 15, 2008


A selection of parasitic protozoa from the UK Natural History Collection. From left to right: Entamoeba histolytica which cause amoebic dysentary; Trypanosoma brucei transmitted by Tetsi flies and causes sleeping sickness; Babesia sp in Red Blood Cells transmitted by ticks; Balantidium coli a very large protozoan of pigs that rarely causes disease; and then two ciliates of cattle both of which are symbionts and cause no disease.

Protozoa are unicellular, eukaryotic,usually motile organisms that are more "animal-like" than "plant-like". More than you need to know about parasitic protozoa can be found here and here.

Protozoa have complex life cycles, some requiring two different hosts for reproduction and/or transmission. You can see some animations of protozoan life cycles at this WHO website. Below is a dipiction of the malaria life cycle which takes place in a mosquito and a human.

Malaria parasites in red blood cells.

You can find out more about protozoa and parasites in general at this CDC website.

The most important protozoan diseases include: Malaria, Leishmaniasis, Trypanosomiasis (African and American), and Amoebiasis. Protozoal infections in the USA are more likely to be Toxoplasmosis, Giardiasis, Babesiosis and Trichomonas.

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