Chapter Overview

Parasitology is the study of infections and diseases caused by protozoans and helminth worms.
Protozoa are small, usually single-celled amebas, ciliates, flagellates, or apicomplexans that may have complex life cycles with several morphological forms.
Protozoan diseases are spread by food, by contact with other humans and animals, or by arthropod vectors.
Protozoan diseases can be managed by drugs, proper hygiene, and vector control.
Diseases caused by infectious amebas include amebic dysentery, and encephalitis. Ciliates are responsible for balantidiosis.
Flagellate diseases include trichomoniasis, giardiasis, trypanosomiasis, and leishmaniasis.
The major apicomplexan diseases are malaria, toxoplasmosis, and cryptosporidiosis.
Helminth parasites are multicellular worms with specialized adaptations in structure and life cycle for feeding, reproduction, and host transmission.
Diseases are spread by eggs and larvae that are eaten or burrow into the skin. Some involve transmission by vector hosts.
Helminth worms include nematodes (roundworms), trematodes (flukes), and cestodes (tapeworms).
Intestinal nematode diseases include ascariasis, hookworm, strongyloidiasis, and trichinosis.
Tissue nematode infections are vector-borne filariasis and onchocerciasis.
Flukes are agents of schistosomiasis and zoonotic liver diseases.
Human tapeworms are acquired from eating poorly cooked beef and pork.
Control of helminth infections is achieved by administering drugs that paralyze or kill the worms and by interrupting their life cycles.

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