- Author: Imad S Dandan, MD; Chief Editor: BS Anand, MD more...
Hydatid disease is a parasitic infestation by a tapeworm of the genus Echinococcus. It is not endemic in the United States, but the change in the immigration patterns and the marked increase in transcontinental transportation over the past 4 decades have caused a rise in the profile of this previously unusual disease throughout North America. This has led to the necessity for physicians to be more aware of its clinical features, diagnosis, and management.
Human echinococcosis is a zoonotic infection caused by the tapeworm of the genus Echinococcus. Of the 4 known species of Echinococcus, 3 are of medical importance in humans. These are Echinococcus granulosus, causing cystic echinococcosis (CE); Echinococcus multilocularis, causing alveolar echinococcosis (AE); and Echinococcus vogeli. E granulosus is the most common of the three. E multilocularis is rare but is the most virulent, and E vogeli is the most rare.
Despite an increase in its occurrence, echinococcosis remains a very rare disease (< 1 case per 1 million inhabitants) in the continental United States. Northern Alaska has endemic areas of E granulosus, but the frequency of infection remains low (< 1 case per 100,000 inhabitants).
Echinococcosis is also unusual in northern Europe. The endemic areas are the Mediterranean countries, the Middle East, the southern part of South America, Iceland, Australia, New Zealand, and southern parts of Africa; the latter 5 are intensive endemic areas. Central Asia, particularly China, is also an endemic area.[1, 2] The incidence of CE in endemic areas ranges from 1-220 cases per 100,000 inhabitants, while the incidence of AE ranges from 0.03-1.2 cases per 100,000 inhabitants, making it a much more rare form of echinococcosis. An epidemiological study of cyctic echinococcosis in Romania emphasized the need for improved preventive measures. Infestation with E vogeli is the most rare form of echinococcosis and is reported mainly in the southern parts of South America.
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Morbidity is usually secondary to free rupture of the echinococcal cyst (with or without anaphylaxis), infection of the cyst, or dysfunction of affected organs. Examples of dysfunction of affected organs are biliary obstruction, cirrhosis, bronchial obstruction, renal outflow obstruction, increased intracranial pressure secondary to mass, and hydrocephalus secondary to cerebrospinal fluid outflow obstruction.
In clinical cases of AE, the mortality rate is 50-60%. This figure reaches 100% for untreated or poorly treated AE. Sudden death has been reported with AE in asymptomatic patients (autopsy diagnosis).
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Because of the restricted geographic distribution of the echinococcal worms, persons of certain races are affected more commonly than others; however, the parasite has the capability of infecting persons of all races equally.
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No sexual predilection is recognized.
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The cysts grow slowly, and a cyst is rarely diagnosed during childhood or adolescence unless the brain is affected.
CE is a disease of younger adults, with an average age at diagnosis of 30-40 years.
AE is a disease of older adults, with an average age at diagnosis of older than 50 years.
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