Few things are as creepy as the thought of a parasite gaining entry to your body. Tapeworms are parasites that take up residence in the intestines of humans or animals. They only choose hosts with backbones, so invertebrates aren't affected by them.
Tapeworms resemble ribbons in shape. As adults, they have teeth, hooks or sucker-like structures on their heads that help them to attach to the inside of the intestine. The body of a tapeworm consists of flat segments, each with its own digestive and reproductive system. As food is being digested and flows past the tapeworm in its host's intestine, the segments absorb nutrients through the tapeworm's skin. The segments of the tapeworm move towards the tail as they become older and new segments are produced near the head of the tapeworm. Once an old segment reaches the end of the tapeworm's tail, the digestive system is gone and only the reproductive system remains, which is merely a sack of eggs by this time. According to the Mayo Clinic, some adult tapeworms can grow to up to 50 feet long and live for up to 2 decades.
The segments of a tapeworm can be pretty small. For example, one segment of the common tapeworm (Dipylidium caninum), which is usually found in dogs and cats, can be just the size of a grain of sand, leading people to think the entire tapeworm is quite tiny. This is a misconception, however, as the whole tapeworm can be about 6 inches or more in length.
There are different types of tapeworms. Some types are usually found in beef (Taenia saginata) while others are more common in pork (Taenia solium) or fish products. According to the CDC, the dwarf tapeworm (Hymenolepis nana) is the most common cause of human infection and is found around the world. It is named "dwarf" because it is only about 1 to 2 inches long. Unfortunately, it most commonly affects human children.
A human infected with tapeworm may not have any symptoms, but he may see segments of adult tapeworm in his fecal matter. When symptoms are obvious, they may include nausea, appetite loss, abdominal pain, diarrhea, weakness and weight loss. Sometimes tapeworm larvae move out of a person's intestine and cause cysts to form in other areas of the body. When this occurs, such symptoms as fever, lumps, bacterial infections and allergic reactions may occur. If the brain is involved, seizures may develop as well. In both animals and humans, medications are used to kill tapeworm. If health-threatening cysts develop, surgery may be required to remove them.
There are ways to prevent human infection with tapeworm. Cooking meat and fish products to at least 150 degrees F will kill these parasites. Since tapeworm eggs are passed out of the intestine through fecal matter, it is possible to prevent the spread by washing your hands well and ensuring that fecal matter doesn't get or stay on the hands, where it can be spread to others. However, the risk of accidental ingestion is increased when sewage is not handled properly and ends up in soil, grass and water. Additionally, it is best to wash your hands after touching a pet's hind quarters or handling its fecal matter, even if you don't think it has a tapeworm.