Echinococcosis, alveolar

The life cycle is similar to that of E. granulosus. In contrast to E. granulosus, rodents (voles, field mice, ground squirrels and shrews) serve as intermediate hosts. Humans become an accidental intermediate host after ingestion of cestode eggs (by eating contaminated berries or through contact with foxes). The primary site of infection is the liver. In contrast to E. granulosus (mostly with a single cyst), an infiltrative cyst is produced which grows like a tumour.

• Distribution is restricted to parts of central Europe, Russia, Canada and Alaska
• Infection is caused by accidental ingestion of soil, berries or vegetables contaminated with E. multilocularis eggs
• Increased infection risk from foxes that adapt to urbanisation and are in close contact with people

• Cysts are usually found in the liver (metastases in lung and brain may follow)
• Growth is not limited by a thick cyst wall, so the cysts can expand at the periphery to produce tumour-like masses
• The disease is often fatal if not treated!

• Incubation time might be one to many years
• Symptoms and signs might manifest rather late when the liver is already heavily parasitised (e.g. upper-right quadrant and epigastric pain, hepatomegaly, allergy)
• Symptoms are earlier when infection affects the lungs or the brain

Diagnostic methods

Parasitological diagnosis
Humans can serve as intermediate host for the fox tapeworm E. multilocularis, which excludes a parasitological diagnosis in stool samples.
With microscopy protoscolices can be detected in cyst fluids from surgical specimens.
Imaging technique (ultrasonography, computed tomography and magnetic resonance imaging) are diagnostically helpful

Molecular diagnosis
PCR detects parasite nucleic acids in needle biopsies or in stool samples of foxes or dogs (final hosts) with excellent sensitivity and specificity

Antigen detection
Several home-made tests detect copro-antigens in the faeces of definitive hosts by ELISA and specific monoclonal antibodies. One test kit is commercially available.

Antibody detection
Serology is an important diagnostic element for detecting alveolar echinococcosis. Various test formats (IFA, ELISAs, Western blots) have been developed to detect specific antibodies with a high sensitivity.
Using an affinity-purified or recombinant antigen (e.g. Em18), a differential diagnosis between the two species seems possible.

Diagnostic strategies

1. To diagnose an individual case
   Combining imaging techniques with serology is the best strategy today.
    
2. To assess endemicity in an exposed population
   Serology is the first choice!

• Individual prevention by educating exposed individuals about the risks of alveolar echinococcosis