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Chapter 2 : Blood and Tissue Protozoa
This section deals with infections caused by blood and tissue protozoa. The freeliving amebae, which have been associated with serious infections, are members of this group. Only two genera of these amebae have been implicated in human infection. Naegleria fowleri causes a fulminant and rapidly fatal infection of the central nervous system, called primary amebic meningoencephalitis. Acanthamoeba species cause amebic keratitis, skin infections, and a more chronic infection of the central nervous system, called granulomatous amebic encephalitis. Balamuthia mandrillaris is a recently recognized free-living ameba that also causes granulomatous amebic encephalitis but acts as an opportunist to cause illness, usually in immunocompromised individuals. Infections caused by the blood and tissue flagellates Leishmania species and Trypanosoma species are also presented in this section. The trypanosomes infecting humans include Trypanosoma brucei variants gambiense and rhodesiense, which cause African sleeping sickness, and T. cruzi, which causes Chagas’ disease. Blood and tissue sporozoa are also included in the section. They include the members of the genus Plasmodium, which cause malaria, as well as those causing babesiosis and toxoplasmosis. The ring like structures characteristic of Babesia microti closely resemble the early stages of the malaria protozoans, especially Plasmodium falciparum. Most of the cases presented in the section may be diagnosed by the preparation and examination of thin and thick peripheral blood films. Although diagnostic methods for babesiosis are also used to diagnose malaria, the former parasites, unlike malaria parasites, may be present in the blood at any time of day.