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In this book, the major protozoan pathogens are grouped according to the location in the body where they most frequently cause diseases. The intestinal and urogenital protozoa are described in this chapter, and the blood and tissue protozoa are described in Chapter 52.

  1. Within the intestinal tract, three organisms—the ameba, Entamoeba histolytica; the flagellate, Giardia lamblia; and the sporozoan, Cryptosporidium hominis—are the most important.

  2. In the urogenital tract, the flagellate Trichomonas vaginalis is the important pathogen.

  3. The blood and tissue protozoa are a varied group consisting of the flagellates Trypanosoma and Leishmania and the sporozoans Plasmodium and Toxoplasma. The important opportunistic lung pathogen Pneumocystis will be discussed in this group, although there is molecular evidence that it should be classified as a fungus.

The major and minor pathogenic protozoa are listed in Table 51–1.

TABLE 51–1Major and Minor Pathogenic Protozoa

Although immigrants and Americans returning from abroad can present to physicians in the United States with any parasitic disease, certain parasites are much more likely to occur outside the United States. The features of the medically important protozoa, including their occurrence in the United States, are described in Table 51–2.

TABLE 51–2Features of Medically Important Protozoa

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