eMedicine Specialties > Pediatrics: General Medicine > Parasitology
Echinococcosis
Updated: Jan 22, 2009
Introduction
Background
Echinococcosis is the general term for 3 diseases caused by the larval stage of Echinococcus tapeworms, the smallest tapeworms in the Taeniidae family. Echinococcus granulosus causes cystic echinococcosis. This species occurs worldwide, typically in rural areas of Africa, the Middle East, southern Europe, Russia, China, Australia, and South America (especially Argentina and Uruguay). Echinococcus multilocularis causes alveolar hydatid echinococcosis and occurs only in the northern hemisphere. Echinococcus vogeli causes polycystic echinococcosis and occurs in Central and South America.
Pathophysiology
The tapeworm's life cycle (see Media file 1) involves a definitive host, usually a dog (although foxes and coyotes have also been implicated), and intermediate hosts such as sheep, goats, and swine. The 3-mm to 6-mm adult tapeworm is found in the definitive host's intestines. Eggs are excreted via the feces into the environment. Dogs typically become infected by eating the remains of infected sheep and other livestock.
Humans are accidental hosts and are not typically involved in the life cycle of the organism. Humans usually become infected through exposure to canine feces. Humans become infected by eating food contaminated with tapeworm eggs, which hatch in human small intestine under the influence of gastric and intestinal secretions. Larvae hatched from these eggs can penetrate the small intestine and become widely distributed in the human body. These larvae develop into a hydatid cyst. In alveolar echinococcosis, the liver is almost exclusively involved. In cystic echinococcosis, the liver is involved in two thirds of cases; in the remaining cases, other sites of involvement, in descending order of frequency, are the lung, spleen, skin, muscle, kidney, retroperitoneum, bone, heart, and brain.
Hydatid cysts may contain many protoscolices, each with the ability to develop into an adult tapeworm in a definitive host. The definitive host usually becomes infected by ingesting the protoscolices in hydatid cysts from the intermediate host; adult tapeworms only develop in the intestines of the definitive host.
Human disease is usually caused by the mass effect of slow-growing hydatid cysts, although bacterial superinfection or allergic symptoms from cyst rupture has also been reported. Because of the hydatid cyst's unhurried growth, infected humans may remain asymptomatic for 20 years.
Frequency
United States
Echinococcosis is rare. Indigenous cases have been reported in Minnesota and among Native Americans in western Alaska. Imported cases are uncommon.
International
Human infection rates are generally highest in areas with poor sanitation practices for sheep-raising, particularly in areas with dogs. Dogs in these areas may become infected by eating the entrails of infected butchered sheep or other herded animals. Humans then become infected when they ingest Echinococcus eggs from dog feces. Human infection rates are also high in areas where intestines are part of the diet.
Echinococcosis has been reported in Manitoba, Canada. Outside North America, incidence rates vary considerably, from less than 1 case per 100,000 people in many parts of the world, to 13 cases per 100,000 people in Greece, 143 cases per 100,000 people in Argentina, 197 cases per 100,000 people in the Xinjiang province of China, and 220 cases per 100,000 people in Kenya's Turkana district.
The Turkana district's particularly high incidence rate is attributed to 2 cultural practices. Some tribes eat canine intestine that has been roasted on a stick over a campfire; disease transmission likely occurs when infected intestine is not thoroughly cooked. Some tribes also do not bury their dead; carnivores may become the direct intermediate host after eating corpses.
Mortality/Morbidity
Most human infection is probably asymptomatic. Death may occur from hydatid rupture, which may lead to anaphylactic shock, or from the extreme progression of cysts in vital organs.
Sex
Males and females are equally affected, according to a Bavarian survey.1
Age
A European study reported most patients infected by E granulosus were aged 21-50 years. Patients infected by E multilocularis were typically older; most were aged 31-80 years.
Clinical
History
- Patients with echinococcosis often remain asymptomatic for many years.
- Routine imaging may reveal incidental evidence of echinococcosis.
Physical
- Echinococcosis symptoms may be secondary to compression of adjacent structures.
- Abdominal pain, a palpable mass, or biliary obstruction is possible.
- Patients with pulmonary involvement may occasionally have respiratory symptoms.
- The location of lesions determines other symptoms.
- Clinical manifestations occur very early in nervous system infection.
- In bone infections, necrosis may occur and cause thin and fragile bone, usually a cause of spontaneous fracture.
- Bacterial superinfection may occur with pyogenic abscess formation within the cyst. Cyst leakage or rupture may lead to allergic symptoms, including the following:
- Loss of appetite is a frequent symptom, and weight loss and weakness may occur. Despite popular belief, hunger pains are uncommon.
- Alveolar hydatid disease may resemble a hepatic neoplasm, with local destruction, biliary obstruction, and occasional metastasis to the brain and lung.
Causes
- Echinococcosis is caused by the larval stage of the Echinococcus tapeworm.
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| Treatment & Medication: Echinococcosis |
| Follow-up: Echinococcosis |
| Multimedia: Echinococcosis |
| References |
| Further Reading |
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References
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Further Reading
See Image 25 and Image 60 at the McGill Faculty of Medicine Web site and The Gorgas Courses in Clinical Tropical Medicine for interesting images and cases.
Keywords
echinococcosis, abdominal pain, alveolar hydatid echinococcosis, anaphylaxis, asthma, biliary obstruction, cystic echinococcosis, Echinococcus infection, Echinococcus granulosus, E granulosus, Echinococcus multilocularis, E multilocularis, Echinococcus vogeli, E vogeli, hydatid disease, hydatidosis, polycystic echinococcosis, urticaria
