Echinococcus multilocularis

Background

Microbiology

• Cestode in the Echinococcus family
• Disease is caused by the larval form

Life Cycle

• Definitive hosts are canid carnivorous animals, including urban coyotes
• Eggs contaminate the environment, including produce
  • They are infective after a few days, and are viable for up to 16 months at 4ºC
• Intermediate hosts (metacestode) are rodents, possibly pigs, and and incidentally humans
• Intermediate host is eaten by the definitive host, completing the life cycle

Epidemiology

• Estimated 18,000 cases annually
• Worldwide in the northern hemisphere
  • Most cases in China (90%), followed by Japan and Russia
  • Rare in North America
• Within Canada:
  • Associated with arctic foxes and wolves
  • Alberta has highest number of cases, with 19 cases from 2013 to 2021
  • 0 to 3 case reports in other provinces

Clinical Manifestations

• Causes alveolar echinococcosis
• Incubation period 5 to 15 years
• Vague abdominal pain may precede diagnosis by years
• Presents as a metastatic malignancy of unknown primary, mot commonly with malaise, weight loss, and right upper quadrant discomfort
  • May also mimic hepatocellular carcinoma, cirrhosis, and tuberculosis
  • Causes continuously-growing tumour-like polycystic mass, made up of multiple vesicles that are lined by laminated germinal layer
• Can cause cholestatic jaundice, cholangitis, portal hypertension, and Budd-Chiari syndrome

Diagnosis

• Combination of radiologic and serologic investigations
• A single negative serologic test does not rule out infection
• May be confirmed by biopsy

Case Definition (Alberta)

• Typical organ lesion detected by imaging with US or CT
• AND histopathology compatible with alveolar echinococcosis
• AND
  • Detection of E. multilocularis by serology
  • OR detection of E. multilocularis by molecular diagnostic methods

Imaging

• Ultrasound or CT demonstrates lesions which typically have an irregular contour, no well-defined wall, central necrosis, and irregular intralesional and wall calcifications

PNM Classification

• P=parasitic mass in the liver, N=neighbouring organ involvement; M=metastases

	P	N	M
X	Primary tumour cannot be assess	Not evaluable	Not evaluable
0	No detectable tumour in liver	No regional involvement	No metastasis
1	Peripheral lesions without proximal vascular and/or biliary involvement	Regional involvement of contiguous organs or tissues	Metastasis
2	Central lesions with proximal vascular and/or biliary invovlement of 1 lobe
3	Central lesions with hilar vascular or biliary involvement of both lobes and/or with involvement of 2 hepatic veins
4	Any liver lesion with extension along the vessels and biliary tree

Management

• Main treatment is surgical resection followed by at least 2 years of antihelminthic therapy (e.g. albendazole)
• Poor prognosis, with 90% 10-year mortality if untreated