Echinococcosis multilocularis

This fact sheet was created 11/15/20.

Cause

There are two main forms of Echinococcosis, a zoonotic disease caused by tapeworm larva; cystic echinococcosis (CE) caused by Echinococcosis granulosus and alveolar echinococcosis (AE) caused by Echinococcosis multilocularis. This fact sheet will focus on E.multilocularis

Significance

Control and prevention of E.multilocularis is difficult due to the wildlife cycle between foxes and small mammals.  Domestic dogs and cats can also carry the tapeworm and are particularly important in zoonotic transmission of this disease.  Around the world, more than 1 million people are affected by echinococcosis at any one time. This disease is often diagnosed late and can be fatal.

Species Affected

Red foxes, coyotes, wolves, lynx, wild cats, and arctic foxes are the principle definitive hosts of E. multilocularis in North America. Dogs and cats can serve as definitive but also as intermediate hosts and are the main link to human infection. Other intermediate hosts include a variety of rodents such as voles, lemmings, shrews and mice.

Distribution

E. multilocularis is confined to the Northern Hemisphere. It occurs mainly in China, Japan, Russia, Europe and North America. In the United States E. multilocularis is found in the region between eastern Montana and central Ohio as well as Alaska. It is also present in Canada.

Transmission

E. multilocularis tapeworm has an indirect life cycle that involves 2 types of hosts; definitive and intermediate. Definitive hosts, commonly carnivores, are asymptomatic but carry adult E. multilocularis worms in their small intestine. Adult tapeworms are small, ranging in size from 1.2 mm to 7 mm in length, and are attached to the small intestine. The mature E.multilocularis produces eggs which are then shed in feces and are immediately infectious. Once in the environment, eggs can be transported by wind, water or insects. They can survive for up to a year in a moist environment at low temperatures.

The eggs are ingested by an intermediate host (rodents) as it feeds on contaminated vegetation or water. Once ingested, the eggs form infective larval multi-chambered cysts throughout the body.  The life cycle is then continued when a definitive host ingests these cysts while feeding on the viscera of an infected intermediate hosts.

Humans are aberrant dead-end hosts meaning that they can become infected by accidental ingestion of E. multilocularis eggs but are not involved in transmitting the infection. Ingestion of tapeworm eggs most commonly occurs through contaminated food such as poorly washed fruits and vegetables, water, soil, or through direct contact with animals hosts like red foxes, dogs and cats.

Clinical Signs

Definitive hosts generally do not show any outwardly signs of infection.

The clinical signs in intermediate hosts are initially asymptomatic. However, the growth of the larvae, which form cysts in vital organs such as the liver and lungs, can lead to illness and death. E. multilocularis can kill rodent intermediate hosts within weeks. Abdominal enlargement, fluid accumulation or ascites, difficulty breathing, vomiting, intermittent diarrhea, and weight loss have all been reported.

In humans, E.multilocularis infection causes Alveolar Hydatid Disease, also known as AE. Infection is characterized by an asymptomatic period of 5-15 years and development of parasitic tumours most commonly in the liver. These cystic tumors are not contained within a capsule but instead are locally invasive. They can completely infiltrate an organ and spread to other organs. In humans, the most common sites of metastasis are the central nervous system, lungs or bones. Weight loss, abdominal pain, lethargy and liver failure are all clinical signs of AE. If untreated, the disease is fatal.

Diagnosis

Infection in a definitive host can be confirmed by identifying the adult tapeworms in the intestines at necropsy. Echinococcus eggs can be detected on fecal examination but are difficult if not impossible to distinguish from eggs of other common tapeworms. Fecal PCR and ELISA tests are more commonly used to confirm infection.  

In the intermediate hosts, the cysts are grossly apparent on internal organs at necropsy.

Treatment

In the definitive host, Echinococcus spp. can be treated with anthelminthic drugs. In intermediate hosts, surgery is often the treatment of choice. Long-term anthelminthic treatment may also suppress some cysts.

Management

Prevention and control of E. multilocularis is difficult because the cycle involves wildlife as both definitive and intermediate hosts.  Although not sustainable, it is possible to treat foxes with praziquantel in bait to decrease the incidence of E. multilocularis, and the risk to other species. There are no vaccines available for wildlife. Dogs and cats living in areas where E. multilocularis is prevalent should be kept from hunting and scavenging wild rodents. To reduce the risk of infection to humans, dogs and cats should be routinely treated with anthelminthic agents.

Individuals at highest risk of developing E. multiloculars infection include: trappers, hunters, veterinarians and others who have contact with wild foxes, coyotes, their stool or household dogs and cats that have eaten wild rodents infected with AE. Gloves should be worn when handling a fox, coyote, or other wild canine, dead or alive.