Echinococcus multilocularis - Alveolar Echinococcosis

Key Messages:

  • Echinococcus multilocularis (E. multilocularis) is a small tapeworm that is found in canids (coyotes, foxes, dogs) and rodents, and is transmitted by the ingestion of feces of infected animals.
  • Ingestion of E. multilocularis eggs can cause alveolar echinococcosis, a slowly progressing disease that can be serious if untreated, and is often difficult to treat.
  • E. multilocularis became a reportable disease in Ontario as of 2018, after the diagnosis of animal echinococcosis in several dogs in Ontario between 2013 and 2018.
  • Persons with exposure to an animal with confirmed shedding of E. multilocularis eggs should be investigated serologically. Prophylaxis should be considered in persons with a high likelihood of egg ingestion and with serologic evidence of infection. 

Alveolar echinococcosis (ICD-10 B67.5-B67.7) is a highly invasive, destructive disease caused by the tapeworm, Echinococcus multilocularis. Infection in humans occurs after the ingestion of eggs, which develop into the larval form, causing multiple, small budding cysts that are usually found in the liver, resembling an invasive tumour.

Untreated alveolar echinococcosis has a high case-fatality rate. Patients eventually die from hepatic failure, invasion of contiguous structures, or less frequently, metastases to the brain.

  • Reservoir: E. multilocularis eggs are shed into the environment primarily by foxes and coyotes (definitive hosts) with gastrointestinal infections with adult tapeworms. Rodents (intermediate hosts) become infected by ingesting fecally-contaminated matter, and, in turn are eaten by foxes and coyotes. Dogs and cats that become infected from hunting wild rodents (such as mice, rats, voles, chipmunks, etc.) can also be sources of human infection.
  • Modes of Transmission: Human (accidental intermediate host) infection occurs after the ingestion of E. multilocularis eggs present in the feces of foxes, coyotes, dogs, or cats who have fed on infected rodents. Fecally soiled dog hair and other environmental fomites also serve as vehicles of infection. There is no person-to-person transmission.
  • Period of Communicability: E. multilocularis eggs shed from definitive hosts are immediately infective for intermediate hosts and are very environmentally stable, remaining infective for approximately one year in a suitable, moist environment at lower temperatures.
  • Host Susceptibility and Resistance: Susceptibility is general. Children are at greatest risk of ingestion of eggs; however, due to the long incubation period, alveolar echinococcosis usually is diagnosed in adults.

Other names in humans: alveolar hydatid disease, multilocular echinococcosis

  • All stages of E. multilocularis’s lifecycle have been detected in Ontario. This includes establishment in coyote and fox populations (definitive hosts) across southern Ontario, with potential hotspots of higher rates of infection in some health units.
  • Since 2012 in Ontario, E. multilocularis was diagnosed in six dogs, three non-human primates, and in one chipmunk. Five of the dogs and all the non-human primates had not travelled outside of southern Ontario. 
  • There have been at least three human cases of alveolar echinococcosis diagnosed in Ontario since 2014, though information on where these may have been acquired is not available. Human cases remain rare in Ontario as from 2018 to 2021 only one  case was confirmed. However, human alveolar echinococcosis is widely distributed in the Northern Hemisphere, especially affecting pastoral societies. 
  • Annual surveillance data for alveolar echinococcosis is published at Public Health Ontario Monthly Infectious Diseases Surveillance Reports and Ottawa Public Health’s Diseases of Public Health Significance Dashboard 

Infection of humans with E. multilocularis is characterized by an initial asymptomatic incubation period of 5 to 15 years. The course of disease is slow. Clinical manifestations depend on the size and location of cysts – because the primary lesion is usually in the liver, infection is often confused with hepatic carcinoma or cirrhosis. Lesions expand at the periphery to produce solid, tumour-like masses (because growth is not restricted by a thick laminated cyst wall).

Symptoms of alveolar echinococcosis are primarily cholestatic jaundice (in about a third of cases) and/or epigastric pain (about a third of cases). In the remaining third of cases, alveolar echinococcosis is detected incidentally during medical examination for symptoms such as fatigue, weight loss, hepatomegaly, or abnormal routine laboratory findings.

Metastases can result in secondary cysts and larval growth in other organs. Larger lesions cause hepatomegaly and epigastric pain. Ascites, malnutrition, jaundice and signs of hepatic failure may occur in later stages of the disease

Sometimes, the primary lesion arrests early in its development (i.e., an aborted infection), and the person remains asymptomatic. Some individuals may present with fully calcified lesions that do not progress. 

Primary cases of alveolar echinococcus cysts are often first detected incidentally on ultrasonography, CT, and/or MRI.

A confirmed case of E. multilocularis requires clinically compatible signs of infection AND laboratory confirmation of infection, including:

  • Demonstration of antibodies to E. multilocularis in blood or serum sample; OR,
  • Demonstration of larval stages of E. multilocularis in histopathology samples from tissue biopsies

Serologic testing for antibodies to E. multilocularis, as coordinated by Public Health Ontario, is performed at the Institute of Parasitology, University of Berne, Switzerland, using a combination of the following assays:

  • Em2-antigen ELISA
  • II/3-10-antigen ELISA
  • Em2Plus-antigen ELISA

Additional confirmatory techniques include direct immunofluorescence and/or echinococcus PCR of tissue biopsies.

For further information about human diagnostic testing, the following resources are available:

Confirmed and suspected cases of Echinococcus multilocularis infection must be reported to Ottawa Public Health as per the Health Protection and Promotion Act. Please call 613-580-2424, ext. 24224 or fax 613-580-9640 (Monday to Friday from 8:30 am to 4:30 pm) to report.

Alveolar echinococcosis is often expensive and complicated to treat, sometimes requiring extensive surgery and/or prolonged drug therapy.  Treatment is informed by the WHO classification of liver cysts. The WHO clinical staging system for alveolar echinococcosis is based on parasitic mass, nodes, and metastases, similar to cancer tumour staging. The WHO states that treatment requires specific clinical experience and patients should be referred to a recognized national/regional alveolar echinococcosis treatment centre or treated under their guidance. Complex questions may require additional assistance available through CDC (404-718-4745; parasites@cdc.gov).

More detailed information on diagnosis and treatment can be found in the WHO manual (2001)  and a 2010 expert consensus on the diagnosis and treatment of cystic and alveolar echinococcosis in humans. The WHO 2010 expert consensus states, the “following principles should be followed: (1) BMZ [benzimidazoles] are mandatory in all patients, temporarily after complete resection of the lesions, and for life in all other cases, (2) interventional procedures should be preferred to palliative surgery whenever possible and (3) radical surgery is the first choice in all cases suitable for total resection of the lesion(s).”

Probable case

During a public health investigation of a case of E. multilocularis, public health staff identify members of the public who are at risk of having ingested E. Multilocularis eggs. Such individuals will undergo serological testing, even if they have no clinical signs of alveolar echinococcosis. Persons demonstrating antibodies to E. multilocularis should be investigated for staging. Prophylaxis should be considered in persons with a high likelihood of egg ingestion and with serologic evidence of infection. In the event that imaging demonstrates no detectable lesion, it may be the case that the patient was exposed to infection without establishment of the parasite.

Personal Preventive Measures

Public health is involved in the education of both pet owners and individuals in high-risk occupations (veterinary staff, wildlife workers, hunters and trappers, etc.) about the lifecycle of the parasite and risks of exposure to E. multilocularis eggs.

  • Hunters and trappers handling foxes, coyotes or other wild canids should wear plastic gloves when handling these animals or their carcasses.
  • Wild fruits and vegetables should not be collected from the ground or eaten. All wild picked foods should be washed carefully or cooked before being eaten.
  • Dogs and cats that have access to wild rodents in areas known to be endemic for E. multilocularis should be dewormed monthly with praziquantel to reduce the risk of exposure to parasite eggs in household environments.
  • Pet owners should prevent dogs and cats from eating rodents.
  • Regular, frequent hand hygiene after handling pets and their feces, and before handling food, can reduce the risk of transmission to humans.

No vaccine for E. multilocularis is currently available.

Public health has a role in the prevention of alveolar echinococcosis, in protecting the public from further transmission of the infection when identified, and in surveillance.

Management of cases, contacts, and outbreaks

While treatment of cases is under the direction of the attending health care provider, public health provides cases with information about the infection and how it is transmitted. Public health investigates cases to identify the likely source of infection and, where appropriate, take action to minimize further risk to the public. This includes the identification of contacts exposed to the same source, so that they may be assessed for serological testing. Close family members and associates of confirmed cases of alveolar echincoccosis should be examined for suspicious cysts or tumours using ultrasound, X-ray, or other imaging modalities.

Consideration of environmental remediation is undertaken by public health, working with cases and contacts. This can include recommendations regarding cleaning and disinfection of implicated environments. Areas inhabited by dogs and cats with known E. multilocularis infections should be decontaminated to prevent risk of exposure to parasitic eggs on surfaces; for example, pet beds, floors, carpets and car interiors.

Dogs with confirmed alveolar echinococcosis may have had a patent intestinal E. multilocularis infection either at the time of diagnosis or historically. As such, Ottawa Public Health ensures that animals with alveolar echinococcosis are treated with anthelmintic drugs, prescribed by a veterinarian. Praziquantel is effective against both juvenile and adult parasites, and is the only treatment currently approved in Canada.

Surveillance

Ottawa Public Health conducts surveillance of suspected and confirmed animal and human cases of alveolar echinococcosis.

Suspected and confirmed human cases of E. multilocularis infection are to be reported by physicians and laboratories to Ottawa Public Health under the Health Protection and Promotion Act. Ottawa Public Health investigates every case of E. multilocularis infection to identify the likely source of infection and, where appropriate, take action to minimize further risk to the population.

Lab Testing

Reporting

General information on Echinococcus multilocularis

International Resources on Echinococcus multilocularis

Contact us:

If you have questions regarding E. multilocularis infection or want to notify Ottawa Public Health about a case of E. multilocularis infection, please contact us at 613-580-2424, ext. 24224.

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