Pathogen (Phylum)


Spread by



Entamoeba histolytica (Protozoa)

severe diarrhea, fever, and gastrointestinal tract hemorrhage

contaminated water or food

E. histolytica is common in developing countries. Drink bottled, boiled, or filter-purified water. Peel fresh fruit, and avoid unpasteurized dairy products.

Sleeping sickness

Trypanosoma sp. (Sarcomastigophora)

swollen lymph nodes, severe headaches, fever, fatigue, and coma

tsetse flies

Tsetse flies are found only in Africa. Wear protective clothing, such as long pants and long-sleeved shirts. Use insect repellent, and avoid open vehicles and bushes.


Leishmania donovani (Sarcomastigophora)

skin sores, swollen glands, fever, and swollen spleen and liver

sand flies

Sand flies are found mostly in tropical and subtropical regions. Stay indoors during the day, when sand flies are most active. Wear protective clothing, and use insect repellents.

figure 25-21

Giardia lamblia is a mastigophoran. The Giardia shown in this picture are shown in their natural habitat—the human intestine.

figure 25-21

Giardia lamblia is a mastigophoran. The Giardia shown in this picture are shown in their natural habitat—the human intestine.


Giardia lamblia, shown in Figure 25-21, causes an illness called giardiasis (JEE-ahr-DIE-uh-sis). Giardiasis is characterized by severe diarrhea and intestinal cramps. Cattle, beavers, and several other animals carry the parasite and contaminate water with their feces. Hikers and other people who are likely to drink this contaminated water are susceptible to giardiasis. Thousands of cases occur annually in the United States. The disease usually is not fatal, and drugs aid recovery. Drinking bottled, boiled, or filtered water prevents giardiasis.


Cryptosporidiosis (KRIP-toh-spawr-I-dee-OH-sis) is characterized by diarrhea and is most often caused by Cryptosporidium parvum, an apicomplexan that lives on the surface of cells lining the small intestine. A stage called the oocyst (OH-sist) can pass in feces from infected animals to humans. An outer shell protects the parasite outside the body, allowing it to survive for long periods and making it resistant to chlorine disinfectants. Cryptosporidiosis is usually not fatal, but it can be dangerous for people with immune disorders. Washing hands thoroughly after coming in contact with feces and avoiding untreated water can prevent cryptosporidiosis.


The mastigophoran Trichomonas vaginalis is responsible for trichomoniasis (TRIK-oh-moh-NIE-uh-sis), a sexually transmitted disease. The parasite does not survive well outside the body, so it is mainly spread by sexual contact. Trichomoniasis is one of the most common sexually transmitted diseases.

Many people do not have symptoms when infected with tri-chomoniasis. However, women are more likely to have symptoms of trichomoniasis than men are. Symptoms include discolored discharge, genital itching, and the urge to urinate. Abstinence from sexual intercourse prevents trichomoniasis.

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