523Table 22–6 DISEASES CAUSED BY PROTOZOA
Protozoan Discussion/Disease(s) Caused
Entamoeba histolyticaNaegleriaspeciesBalantidium coliGiardia lambliaTrichomonas vaginalisTrypanosomaspeciesPlasmodiumspeciesToxoplasma gondiiCryptosporidium
speciesBabesia microtiand
other speciesAmebic dysentery; ulcerative lesions in the colon, bloody diarrhea; abscesses may form in the
liver, lungs, or brain. Spread by the fecal–oral route in water or food.
Amebic meningoencephalitis: inflammation of the meninges and brain; uncommon in the
U.S. but almost always fatal. Amoebas in fresh water are acquired when swimmers sniff
water into the nasal cavities; the amoebas move along the olfactory nerves into the brain.
Balantidiasis: abdominal discomfort and diarrhea; often mild. Reservoirs are pigs and other
domestic animals; spread by the fecal–oral route.
Giardiasis: fatty diarrhea; may be mild. Reservoirs are wild and domestic animals and people.
Spread by the fecal–oral route in water or food prepared by people with mild cases. An
important cause of diarrhea in daycare centers.
Trichomoniasis: a sexually transmitted disease. Women: causes cervicitis and vaginitis; men are
often asymptomatic.
African sleeping sickness: lethargy progressing to coma and death. Reservoirs are wild and
domestic animals; vector is the tsetse fly. No vaccine.
Malaria: the protozoa reproduce in red blood cells, causing hemolysis and anemia. The vector
is the Anophelesmosquito. Cerebral malaria is the most severe form, and it is often fatal for
children. The WHO estimates that at least 500 million people are affected, and 3 million
people die each year of malaria. Several promising vaccines are in the testing stages.
Toxoplasmosis: asymptomatic infection in healthy people. Congenital infection: miscarriage or
mental retardation, blindness. Reservoirs are cats and grazing animals. Pregnant women
may acquire cysts from cat feces or from ingestion of rare beef or lamb.
Diarrhea: ranges from mild to severe; spread by the fecal–oral route. An important cause of
diarrhea in daycare centers and in AIDS patients. Is very resistant to chlorine, may contam-
inate municipal water supplies or swimming pools and cause extensive epidemics.
Babesiosis: first symptoms similar to influenza; the protozoa reproduce in and destroy RBCs. In
severe cases the hemolytic anemia may lead to renal failure. The vectors are Ixodesticks.
No vaccine.Table 22–7 INFESTATIONS CAUSED BY WORMS
Worm (Genus) Discussion/Disease(s) Caused
Chinese liver fluke
(Clonorchis)
Tapeworms(Taenia,
Diphyllobothrium)
Pinworm(Enterobius)Hookworm(Necator)AscarisTrichinella spiralisAbdominal discomfort; cirrhosis after many years. Adult worms (1/2 inch) live in bile ducts.
Acquired by people from ingestion of raw fish that contains worm cysts.
Bloating and abdominal discomfort; constipation or diarrhea. People acquire the worms by eat-
ing poorly cooked beef, pork, or fish (the alternate hosts) that contain worm cysts.
Adult worms (1/8 inch) live in colon; females lay eggs on perianal skin while host is asleep,
causing irritation and itching of skin. Eggs are spread to family members on hands and bed
linens. In the U.S., this is probably the most common worm infestation.
Adult worms (1/2 inch) live in the small intestine; their food is blood. Heavy infestations cause
anemia and fatigue. Eggs are excreted in feces; larval worms burrow through the skin of a
bare foot and migrate to the intestine. Worldwide, in tropical and subtropical regions, an
estimated 800 million people are infested. Hookworm is now rare in North America.
Adults are 10–12 inches long, and live in the small intestine. Large numbers of worms may
cause intestinal obstruction. Eggs are excreted in feces and are spread to others on hands or
vegetation contaminated by human feces.
Trichinosis: severe muscle pain as migrating worms form cysts that become calcified. Acquired
by eating poorly cooked pork (or wild animals) that contains cysts.