This chapter offers a brief survey of the protozoan and helminthic parasites of medical importance. A synopsis of each parasite is provided within tables that are organized by the organ system that is infected (eg, intestinal and blood/tissue protozoan infections and intestinal and blood/tissue helminthic infections). Key concepts are provided at the beginning of the protozoa and helminths sections to give the reader an overview of the paradigms in medical parasitology. Current updates to information provided in this chapter can be found at the Centers for Disease Control and Prevention (CDC) website www.cdc.gov/ncidod/dpd.
CLASSIFICATION OF PARASITES
The parasites covered in this chapter are categorized into two major groups: parasitic protozoa and parasitic helminths.
Protozoa are unicellular eukaryotes that form an entire kingdom. Classifying protozoan parasites into taxonomic groups is an ongoing process, and their status is often in a state of flux. For this reason, this chapter separates the parasitic protozoa into four traditional groups based on their means of locomotion and mode of reproduction: flagellates, amebae, sporozoa, and ciliates. Table 46-1 lists several medically important protozoan parasites by the organ system they infect, the mode of infection, diagnosis, treatment, and geographic location.
TABLE 46-1Synopsis of Protozoan Infections by Organ System |Favorite Table|Download (.pdf) TABLE 46-1 Synopsis of Protozoan Infections by Organ System
|Parasite/Disease ||Site of Infection ||Mechanism of Infection ||Diagnosis ||Treatment ||Geographic Area |
|Intestinal protozoa |
Giardia lamblia (flagellate)
|Small intestine ||Ingest cysts in water, not killed by normal chlorination ||Stool exam for O&P; EIA for antigens ||Metronidazole or nitazoxanide ||Ubiquitous: campers, ski resorts, dogs, wild animals, especially beavers |
Entamoeba histolytica (ameba)
|Colon; liver; other organs ||Ingest cysts from fecal contamination of water or food or oral/anal behaviors ||Stool exam for O&P; EIA for antibodies and antigen ||Iodoquinol, or paromomycin ||Worldwide wherever fecal contamination occurs |
|Small intestine; respiratory tract ||Ingest oocysts, fecal contamination ||Stool exam/acid-fast staining; direct-fluorescent staining; EIA for antigens ||Nitazoxanide for immunocompetent ||Ubiquitous, especially in cattle-raising areas |
|Small intestine ||Oocysts from fecal contamination of water, fresh produce ||Stool exam—acid-fast staining, UV fluorescence microscopy ||Trimethoprim/sulfamethoxazole ||Worldwide, tropics, subtropics |
|Sexually transmitted protozoa |
Trichomonas vaginalis (flagellate)
|Vagina; males usually asymptomatic ||Trophozoites passed from person to person through sexual intercourse ||Microscopic exam of discharge, urine, tissue scraping ||Metronidazole for both partners ||Ubiquitous in sexually active populations |
|Blood and tissue flagellates |
Trypanosoma brucei rhodesiense
East African trypanosomiasis, sleeping sickness
|Blood, lymph ||Tsetse bite (painful) lacerates skin and releases trypomastigotes ||Trypomastigotes (extracellular) in blood smear, CSF, or lymph node aspirate; serology (CATT) || |
Hemolytic stage: Suramin
Late CNS involvement: Melarsoprol
|East Africa; antelope, bushbuck are animal reservoirs for human infection |
Trypanosoma brucei gambiense
West African trypanosomiasis, sleeping sickness
|Blood, lymph ||Tsetse bite (painful) lacerates skin and releases trypomastigotes ||Trypomastigotes (extracellular) in blood smear, CSF, or lymph node aspirate; serology (CATT) |
Hemolytic stage: pentamidine
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