Tapeworms are parasites that typically cause harmless infections in humans. However, sometimes they can cause serious illness. Four different types of tapeworm cause most cases of human infection: pork, beef, dwarf and fish tapeworms.

Most people are infected with a tapeworm after consuming food or water contaminated with tapeworm eggs or larvae. Once a person ingests the eggs or larvae, the organisms travel to the intestines, where they develop and mature. An adult tapeworm can measure up to 33 feet (10 meters) long and live inside the body for up to 20 years.

In the United States, tapeworm infections are relatively rare due to routine inspection of domestic food animals and laws that restrict certain feeding practices. Tapeworm infections are more common in countries that have less restrictive laws regarding livestock and where sanitation is inadequate.

Certain factors increase the risk of contracting a tapeworm infection. These include infrequent washing and bathing, exposure to livestock, traveling to foreign countries with poor sanitation and eating raw or undercooked meat or fish. In addition, people with weakened immune systems may have an increased risk of tapeworm infection.

In most cases, people infected with tapeworm do not experience symptoms. However, some people may notice eggs, larvae or portions of an adult tapeworm (proglottids) in their stool. Other symptoms that may accompany a tapeworm infection include abdominal pain, diarrhea and loss of appetite.  

Tapeworm infections usually do not pose immediate health risks. However, complications can develop in some people if the infection is left untreated. Tapeworm infections confined to the intestines are usually successfully treated with medication. Treatment may be more difficult if the infection has spread to other parts of the body. In severe cases, surgery may be necessary to remove cysts from areas of the body such as the liver, lungs or other organs.

Tapeworm infections may be prevented by practicing good hygiene, such as frequent and thorough hand washing. People also are urged to exercise caution when traveling in developing countries, because sanitation may be poor and meat may be more likely to be contaminated.