Tapeworm is a parasitic organism that lives in hosts like pets, farm animals, and humans. Making up the class Cestoda, tapeworms are long, segmented worms of different species with a complicated reproductive cycle. A tapeworm infestation often has minimal symptoms, but a person can develop serious health problems if it goes untreated.

A tapeworm has a head, called the scolex, with a mouth of hooked appendages that allow it to attach to its host's intestinal lining. Right behind the head, the neck grows the segments that make up the rest of the elongated worm. A healthy, mature tapeworm can reach 20 ft (6.1 m) in a large host, winding down its small intestine. The end or tail segments break off and are passed with excrement.

In its adult phase, tapeworm absorbs nutrients from its primary host, which could be a dog, cat, cow, sheep, human, or other mammal. To reproduce, the tapeworm can fertilize its own eggs (in some species) and release them to be excreted with the host's stool. In the secondary phase, an intermediary host ingests these eggs, and they get embedded in muscles or organs. When the intermediary host, such as a cow, gets eaten by another primary host, the eggs begin to develop into new tapeworms.

Tapeworm is frequently picked up by swimming in a body of water, like a lake or river, and accidentally swallowing a small amount of water. However, one can also be infected by eating undercooked meat, such as beef, pork, or fish, or by getting bitten by a flea from an infected pet. Humans with tapeworm have subtle or nonexistent symptoms. These include weight loss, hunger, indigestion, weakness, diarrhea, nausea, vomiting, or anemia. If the tapeworm has spread, using you as an intermediate host, and embedded eggs in vital organs, your liver, lungs, heart, and brain can be affected.

Your family doctor can diagnose a tapeworm infestation by examining a stool sample for segments or eggs from a worm that has used you as their primary host. However, if the human is acting as secondary host, and cysts have formed in organs, a doctor may need to conduct a CT or ultrasound scan. Treatment of a tapeworm infestation relies on medicine, but cysts need to be surgically removed.