Ingestion
Tapeworms, as the Mayo Clinic explains, are caused by the ingestion of food that has been contaminated with tapeworms. People can get tapeworms either by inadvertently consuming tapeworm eggs or tapeworm larvae. If a person eats tapeworm larvae, the larvae matures into an adult tapeworm in the intestines. The tapeworm then latches onto the intestinal wall using its teeth and produces eggs. If tapeworm eggs, on the other hand, are eaten, they can get outside of the intestines and form cysts in the body's tissues. This kind of tapeworm infection can be very dangerous because the cysts can cause serious organ damage.
Undercooked Food
Once source of tapeworm is food that has not been prepared properly and thoroughly cooked. As the Food Safety and Inspection Service explains, undercooked pork and beef can have larvae in them. These larvae are present in cysts within the meat and may survive if the meat is not cooked thoroughly. Oddly enough, even though the larvae can live in pork and beef, humans are the definitive host for tapeworms. That means that tapeworms only produce eggs when they are in humans, though the eggs can survive outside of humans and can develop into larvae in other animals.
Fecal Infection
Because tapeworms only produce eggs when they are in humans, another source of a tapeworm infestation is inadvertent consumption of human feces. This is more common in underdeveloped areas, where food may not be properly cleaned or is washed in contaminated water. In some cases, people with a tapeworm infestation can reinfect themselves with eggs (due to poor personal hygiene), which can cause the eggs to get outside of the intestines and form cysts.
