Tapeworms, or cestodes, cycle through three stages--eggs, larvae and adults. In humans, the adults reside in the gastrointestinal tract, and the larvae live in almost every organ. When the the larvae have penetrated tissues, they develop into several encapsulated forms, among them a cysticercus and a hydatid cyst. Disease can be caused either by the adult form or by the larvae, depending on the specific species of tapeworm.
Cysticercosis
Cysticercosis is an infection caused by pork tapeworm, or Taenia solium. According to the Centers of Disease Control and Prevention, infection is more common in poorer societies, where meat may be undercooked, and rare in Muslim countries, where consumption of pork is generally forbidden. According to "Harrison's Principles of Internal Medicine," cysticerci are most commonly found in the central nervous system, eyes, muscles and subcutaneous tissues. Neurological symptoms predominate, including seizures, accumulation of fluid in the brain and increased intracranial pressure. Headache, nausea, vomiting and confusion are common. Strokes and meningitis can occur. Treatment is aimed at controlling the symptoms, such as seizures, and eradicating the parasite with anti-parasitic drugs such as praziquantel.
Echinococcosis
Echinococcosis is caused by echincoccus, a parasite with a complicated life cycle involving transmission through several animals, including sheep and dogs. According to "Harrison's Principles of Internal Medicine," infection is most common where livestock live in close contact with dogs. In humans, the cysts most often settle in the lungs and in the liver, where they can remain for years without causing symptoms, as they gradually enlarge. Common symptoms include abdominal pain and jaundice. Rupture of a cyst can cause fever and anaphylaxis, a severe allergic reaction that left untreated can lead to death. Cysts in the lungs cause symptoms that include shortness of breath, chest pain and bloody sputum. Treatment of echinococcosis consists of surgical removal of the cysts along with anti-parisitic medications.
Diphyllobothrium Infections
These worms are found in lakes and rivers in the northern hemisphere, central Africa and Chile. According to "Harrison's Principles of Internal Medicine," the adult worm attaches to the ileum, a section of the intestines. It can grow to a length of 25m. Infection is often asymptomatic. When symptoms do occur, they can include abdominal pain, vomiting, weakness and weight loss. Less frequently, intestinal obstruction or gallbladder disease may occur. The tapeworm interferes with absorption of vitamin B12, leading to anemia and neurological complications, including gait disturbances and dementia.
References
- Department of Parasitic Diseases, The Centers for Disease Control and Prevention: Echinococcosis
- Department of Parasitic Disease, The Centers for Disease Control and Prevention: Taeniasis
- "Harrison's Principles of Internal Medicine, 17th Edition"; Antoni Fauci (ed); 2008
