Tapeworms are a type of parasite that can live inside a person's intestines. Doctors may refer to tapeworms as cestodes. Tapeworms are a type of flatworm with a long ribbon-like body with many segments, sometimes growing 4.5-9m (15-30ft) in length. They have a small head with hooks and suckers.
How common are tapeworm infections?
Tapeworm infections in the UK are rare, but they are more common in developing countries. There are several types of tapeworms including:
- Echinococcus granulosus, the dog tapeworm
- Taenia solium, the pork tapeworm
- Taenia saginata, the beef tapeworm
- Diphyllobothrium latum, the fish tapeworm
- Hymenolepis nana, the dwarf tapeworm
The dog tapeworm is common is Greece, southern Spain, Turkey, South and North America, eastern Australia, Africa and Asia. It also occurs in the UK in some rural areas, especially around sheep farms in Herefordshire, mid-Wales and Scotland. A dog tapeworm infection is known as hydatid disease. About 10 to 20 cases are reported in the UK each year.
The pork and beef tapeworms are more often found in Africa, the Middle East, Eastern Europe, South-east Asia, and Central and South America. The fish tapeworm occurs most often in countries in which eating raw fish is common: Eastern Europe, the Scandinavian countries and Japan. The dwarf tapeworm is common in children living in unhygienic conditions, especially where there are fleas - in this case insects including fleas pass the eggs from the droppings of infected rodents to humans.
How do tapeworms develop?
Tapeworms have a three-stage lifecycle. Stage one occurs when an animal or fish swallows the eggs, which normally happens when eating food or drinking water contaminated by infected faeces (stools). The larvae (newborn worms) develop in stage two when inside the animal or fish. The eggs hatch into larvae that burrow through the walls of the intestines. They travel through the bloodstream to muscles, where they form into cysts full of larvae.
In stage three, humans consume the cysts when eating contaminated meat or fish. The cysts can survive if the consumed food is undercooked, or in the case of fish, if it is raw. Once inside a human's intestines, the cysts hatch and develop into adult worms, growing and producing eggs. The eggs pass out of the human in faeces, allowing the cycle to continue.
However, humans can swallow the eggs from pork tapeworms directly, which allows the cysts to form inside the human body before becoming adults.
If the tapeworm larvae of the pork tapeworm settle outside a person's intestines, they can cause other illnesses.
How can humans get tapeworms?
Poor hygiene is the most likely method of acquiring tapeworms. A person can get tapeworms by:
- Eating raw or undercooked contaminated pork, beef or fish such as salmon
- Swallowing food or water that contain contaminated faeces (stools), even if only a trace amount
- Touching contaminated faeces and then touching their mouths with contaminated hands