Alveolar echinococcosis (ORPHA:284)
A rare parasitic disorder that occurs after ingestion of eggs of Echinococcus multilocularis and characterized by an initial asymptomatic incubation period of many years followed by a chronic course where the clinical manifestations include epigastric pain and jaundice.
Epidemiology
E.multilocularis is endemic in the northern hemisphere and central Europe and the incidence in Europe is estimated to range between 1/10,000,000-1/330,000. Hot spots are in Western parts of China and Central Asia. People at high risk include dog-owners, including farmers, or others who have contact with wild foxes, or their stool.
Clinical description
The peak age group in Europe is 50-60 years. After an asymptomatic period of >10 years, the parasite invades mainly the liver forming slow-growing, minute vesicles comparable to a sponge. As the lesion gets larger, the central part may become necrotic, and appears as a pseudocyst. Calcifications can frequently be seen. The clinical manifestations include epigastric pain and jaundice which may be followed by fever, anemia and weight loss. Invasion of the bile ducts leads to cholangitis, portal hypertension, and biliary cirrhosis. The disease can progress to the cirrhotic stage after a long latent, asymptomatic period. Extrahepatic manifestation as primary disease is very rare (1%). 13% of cases present as multiorgan disease where the metacestode infiltrates the neighborhood of the liver, and/or sets metastasis involving the lungs, spleen, bones and/or brain. Lung or brain involvement is characterized by exertional dyspnea, dysarthria, hemiparesis and cranial nerve palsies.
Etiology
Alveolar echinococcosis (AE) occurs after ingestion of eggs of the parasite E.multilocularis. Wild carnivores, mainly foxes, are the most important definitive hosts but domestic dogs and cats may also serve as definite hosts by ingestion of infected wild rodents. Human are accidental intermediate hosts and are affected by the intermediate metacestode stage of the parasite.
Diagnostic methods
Diagnosis of AE is based on: typical organ lesions detected by imaging techniques such as ultrasound (large hepatic mass with juxtaposed areas of internal hyper- and hypoechogenicity, irregular margins, and scattered calcification, and/or a pseudocyst with a large area of central necrosis surrounded by an irregular ring-like region of hyperechogenicity representing fibrous tissue), CT (indistinct solid tumors with central necrotic areas, plaque like calcifications), and MRI; detection of specific serum antibodies by ELISA or by immunochromatographic test; specific staining of metacestode in histo-or immunohistopathology; and detection of E. multilocularis nucleic acid in a clinical specimen.
Differential diagnosis
Differential diagnosis includes benign or malignant neoplasms, focal hepatic lesions, and abscesses.
Management and treatment
The mainstay for AE treatment remains an interdisciplinary management guided by gastroenterologists, surgeons, radiologists and parasitologists. Radical surgery is indicated if lesion can be excised with safety margins. Long-term antiparasitic treatment with albendazole is mandatory. Preventive measures include avoidance of contact with fox feces, use of praziquantel-impregnated baits, regular treatment of dogs or cats with praziquantel, as well as hand washing and improved hygiene.
Prognosis
AE is one of the most dangerous zoonotic diseases in the world and if untreated prognosis is poor. Early diagnosis and treatment of AE, especially during the asymptomatic period, are important for reducing morbidity and mortality. Patients succumb to hepatic failure, invasion of contiguous structures, or, less frequently, involvement of the brain. Mortality rates have traditionally been high, ranging between 50% and 75%. However, in recent years major achievement has been reached by careful management of AE cases, and life-expectancy of patients is approaching that of the general population.

                            Last update: 
                            June 2014