Parasitic Diseases

Medical Parasitology

One of the largest fields in parasitology, medical parasitology is the study of those parasites that infect humans. These include organisms such as:

The eggs of the human parasite Enterobius vermicularis, or ‘'human pinworm,” captured on cellulose tape.

• Plasmodium spp., the unicellular organism that causes malaria
• Leishmania donovani, the unicellular organism that causes leishmaniasis
• multicellular organisms such as Schistosoma spp

The study of medical parasitology is commonly conceived as limited to parasitic worms (helminths) and the protozoa. But others organisms, such as vectors (insects) and/or ectoparasites are usually included.

In the protozoan are located the most important parasitic pathogens, such as those that cause malaria, but also many associated with a high morbidity in the intestinal tract. Of the many protozoa that can reside in the human gut, only the invasive strain of Entamoeba histolytica causes serious disease. This parasite, ingested in water contaminated with human feces containing viable cysts of E. histolytica, can cause the disease amebiasis, which in its most severe form is known as amebic dysentery. Another common waterborne intestinal protozoon is the flagellate Giardia lamblia/duo-denalis/intestinalis, which causes giardiasis, a mild to occasionally serious or long-lasting diarrhea.

Other flagellate parasites infect the human skin, bloodstream, brain, and viscera. The tsetse fly of Africa carries to humans the blood-infecting agents of trypanosomiasis, or African sleeping sickness, Trypanosoma brucei gambiense and T. brucei rhodesiense. The infection can be fatal if the parasites cross the blood-brain barrier. In Latin America, the flagellate T. cruzi[Page 1336]is the agent of Chagas’ disease, a major cause of debilitation and premature heart disease among those who are poorly housed. The infection is transmitted in the liquid feces of a conenose bug (genus Triatoma) and related insects. The infective material is thought to be scratched into the skin or rubbed in the eye, especially by sleeping children.

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