LIVER AND BILIARY TREE PARASITES
CESTOIDEA Order: Cyclophyllidea

ECHINOCOCCUS MULTILOCULARIS

AE1-ic

The “small fox tapeworm” Echinococcus multilocularis (E.multilocularis)
causes alveolar echinococcosis (AE) in intermediate hosts.

( 1 ) E.multilocularis is a small tapeworm (1,2-4,5 mm in lenght)
that parasites red and arctic foxes (dogs  and cats  are the definitive hosts).
Definitive hosts are always carnivores.



( 2 ) In the definitive hosts the adult tapeworm, consisting of 2 to 6 proglottids,
lives attached to the luminal surface of the small intestine.
The terminal proglottid contains mature eggs (ovoid, 30-40 µm in diameter).



( 3 ) The embryonated eggs, the infectious stage, are long-lived
and highly  resistant to high and low temperature (more than 50° C and down to -40° C).
The mature eggs are shed with faeces and are spread in the environment.
It is assumed that the intermediate host acquires the infections
through the ingestion of contaminated fruits and vegetables.



( 4 ) When the intermediate hosts (predominantly rodents
or other small mammals, or, accidentaly, humans) ingest eggs,
the onchosphere hatches from the egg in the duodenum.



( 5 ) The activated oncosphere penetrates the small intestine,
enters blood vessels and reaches primarly the liver via the portal vein;
In the liver the oncosphere proliferates into the metacestode surrounded
by an inner germinative membrane and an outer laminated layer.



( 6 ) The lifecycle is completed when an intermediate host,
carrier of viable protoscolices within the cysts, is devoured by a definite host.

Human AE is prevalent in North America (Alaska and northern Canada),
in Europe (France, Switzerland, Austria and Germany),
in Asia (from the White Sea to the Behring strait in the north and from Turkey,
through Afghanistan, Iran, India, China, Mongolia to north Japan in the south).
The annual incidence of human disease varies from
28 cases/100.000 inhabitants in Western Alaska (St. Lawrence Island included),
to 0.18-4,4/100.000 in Central Europe.

The liver is the organ primarily affected;
metastases are mainly observed in cases
of advanced disease and may affect almost any organ.
The disease either spreads via direct contact or via blood vessels.
Secondary AE mostly affects the brain, the lungs,
soft tissue, the spine and other bony structures.
The disease is primarily characterized by an expansive
and infiltrative growth in the liver.
Clinical features may be absent for many years
and mostly become apparent in advanced disease.
They may include hepatomegaly, jaundice, abdominal pain, weight loss,
fever and manifestations of secondarily affected organs.

For diagnosing AE the clinician mainly relies on morphological criteria
together with serology and epidemiological aspects.

AE4-ic	AE5-ic	AE6-ic

       On ultrasound a typical lesion demarcates as
a heterogeneous hypoechoic lesion with irregularly shaped margin
and often contains focal areas of calcification ( 50% of cases).
The appearance on ultrasound is highly variable between cases
as can be appreciated on the images above.
It is the ideal method for screening purposes and short-term follow-up.

AE2-ic	AE3-ic	AE-M-ic

        Computed tomography (CT) and magnetic-resonance-imaging (MRI)
are used for further characterization of the lesion.
They are indispensable for the evaluation of extrahepatic affection in AE
and they are used for a preoperative evaluation.
CT best depicts the typical calcifications and it is used
for follow-up examinations at longer intervalls.
For serology an ELISA was established based on the purified E.multilocularis
carbohydrate antigen Em2 (derived from the laminated layer).
It is the reference test for diagnosis and it may
allow discrimination of AE from E.granulosus infection.
However, in a significant percentage of cases the two species
cannot be differentiated simply by serological means.

The only curative treatment for AE to date
is total surgical resection combined with chemotherapy.
Drugs used for the treatment of AE are benzimidazoles
(mebendazole 50mg/KG and albendazole 10-15mg/KG).
Chemotherapy is mainly parasitostatic and may therefore not be considered curative.
In inoperable or incompletely resected cases chemotherapy has to be administered
for extended periods of time and often results in life-long treatment.