Helminth Infections

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Tapeworm Infection
A number of tapeworms infect humans, but three are the most common; Hymenolepis nana, Taenia saginata, and Taenia solium. Hymenolepis nana is the most common tapeworms of humans, infecting an estimated 75 million people worldwide, mostly children. This tapeworm is also a common parasite of rodents. The parasite has an indirect life cycle in which the adult tapeworms mate in the small intestine. Eggs that are passed in the feces may infect another human or rodent host directly or may infect a grain beetle intermediate host. Humans may become infected by ingestion of the eggs in contaminated food or water, or by ingestion of infected beetle intermediate hosts.

Most intestinal tapeworm infections are light and are therefore asymptomatic. Symptomatic infection is typically mild and ill-defined. The most common symptoms of infection include diarrhea, abdominal discomfort, anorexia, and nausea. Intestinal tapeworm infections are easily treated with the drugs praziquantel or niclosamide, which result in a complete cure.

The beef tapeworm, Taenia saginata and the pork tapeworm Taenia solium are two tapeworms that occur in humans. Adult tapeworms live in the small intestine where they mate. Eggs are passed in the feces. The intermediate hosts in the life cycles of these tapeworms are cattle and pigs respectively. The intermediate hosts become infected when they ingest the eggs on pasture or food that is contaminated with human feces. Humans become infected by ingesting larval tapeworms that are in raw or poorly cooked beef or pork. Adult worms are quit large and may exceed 30 ft. in length. Worldwide about 77 million people are infected with the pork tapeworm and about 10 million people are infected with the beef tapeworm.

There is a unique component in the life cycle of the pork tapeworm, T. solium, that makes it a particularly dangerous parasite. In addition to serving as the definitive or final host in the life cycle, humans may also assume the role of intermediate host (that normally exhibited by the pig. In this instance, humans swallow the eggs, becoming infected with the larval tapeworms, called cysticerci. This serious disease, known as cysticercosis, may involve the eyes leading to blindness or the brain leading to neurological problems and even death.