Echinococcosis and Taeniasis

Echinococcosis & Taeniasis

Causative Agent

Echinococcosis:

Parasitic and zoonotic disease of mammals caused by infection with tapeworms of the genus Echinococcus.
Echinococcus granulosus and E. multilocularis are found in BC.
Definitive and intermediate hosts are both mammals.
Infection with Echinococcus causes little or no harm to the definitive host; however, larval stages within intermediate hosts can be highly pathogenic.

Taeniasis:

Parasitic disease of mammals caused by infection with tapeworms of the genus Taenia.
Taenia ovis krabbei is known to be present in BC.
Definitive and intermediate hosts are both mammals.
Infection with Taenia causes little or no harm to the definitive host; however, larval stages within intermediate hosts can be pathogenic

Images

Click on a photo to enlarge.

Cysts of E. multilocularis in the liver of a muskrat.

Caribou lungs with hydatid cysts ( E. granulosus).

Generalized Echinococcus sp. life cycle.

Distribution

Geographic:

Echinococcus granulosus is widely distributed across Canada.
Echinococcus multilocularis has a more limited distribution: AB, MB, SK, NWT.
Taenia ovis krabbei is found throughout Canada.

Seasonality:

Carnivores can act as reservoirs all year long – herbivores obtain infection from consuming contaminated vegetation when it is available.

Hosts, Transmission and Life Cycle

E. granulosus

Hosts:

Definitive (adult worm): wolves, coyotes, domestic dogs
Intermediate (larval worm): Cervids , particularly moose, caribou and elk and bighorn sheep in western Canada.
Humans can act as intermediate hosts but are considered to be “dead-end” host since they are not usually consumed by carnivores.

E. multilocularis

Hosts:

Definitive (adult worm): Arctic and red foxes, coyotes, sometimes domestic dogs and cats.
Intermediate (larval worm): rodents (voles, mice, muskrats).
Humans again can act as intermediate hosts but are considered to be “dead-end” host since they are not usually consumed by carnivores.

Transmission and Life Cycle of Echinococcus: See Life Cycle above.

Life cycle is similar between E. granulosus and E. multilocularis with differences in host species and larval growth characteristics.
Adult worms occupy the small intestine of infected carnivores and eggs are voided in the feces, usually a month after initial infection.
Eggs from the feces contaminate vegetation, are are subsequently eaten by intermediate, herbivorous hosts.
Larvae move to preferred sites within the intermediate host, usually lung or liver (or less frequently, the muscle or eyes), where they form often large and obvious fluid-filled “hydatid” cysts containing many larvae.
Cysts are consumed by carnivores, breaking open to release immature worms.
Larvae then mature into adult worms after attaching to the wall of the small intestine, subsequently releasing eggs with the feces.

Taenia ovis krabbei

Hosts:

Definitive (adult worm): wolves, coyotes, domestic dogs, cougars, bears.
Intermediate (larval worm): Cervids, caribou, and elk, Rocky Mountain bighorn sheep.

Transmission and Life Cycle of Taenia ovis krabbei.:

Life cycle similar to Echinococcus spp.
Adult worms occupy the small intestine of carnivores and omnivorous mammals.
Larvae form cysts, mainly in the skeletal muscles and associated connective tissue of ungulates.

Signs and Symptoms of Echinococcus sp. and Taenia ovis krabbei

Adult worms have no detrimental effects on the carnivore host.

E. granulosus:
Larval cysts may cause problems in host tissue because of the continual growth and expansion of the cyst.
The structure of the wall of the cysts forms a tissue/host barrier enabling tissues of the host to “wall” off the cysts itself, preventing further spread.
Subsequent compression of tissues, such as the lung, may cause debilitation due to the animal’s reduced ability to breathe if a sufficient number of cysts are involved.

E. multilocularis:
More dangerous than E. granulosus as the larval cysts grow rapidly and bud externally acting very much like an invasive cancer.
Unlike the cysts of E. granulosus, the structure of the wall of the cysts of E. multilocularis does not form a tissue/host barrier, allowing the cyst to further invade tissues via the lymph or blood.
E. multilocularis severely debilitates and often kills its rodent host.

Taeina ovis krabbei:
Larval forms have been associated with significant tissue damage and loss of body condition in infected herbivores, but most infections are noted accidentally during butchering of hunted animals.

Meat Edible?

Humans are not capable of harbouring adult Echinococcus tapeworms and so cannot become infected either by handling or eating hydatid cysts - for aesthetic reasons, cysts should be removed prior to consumption.
Humans can be infected by consuming the infective eggs passed by the carnivore hosts of Echinococcus spp. For this reason, those who handle live carnivores, their feces, pelts or carcasses should wear gloves and use good hygiene to avoid contamination by tapeworm eggs.
Taenia ovis krabbei is not transmissible to humans during any part of its cycle – cysts noted in meat are not aesthetically pleasing but are killed during normal cooking temperatures and by freezing.
Meat of animals infected by these parasites should not be fed to dogs since dogs can be hosts for the adult tapeworms. Also, infected viscera should be destroyed by burning to prevent transmission to domestic dogs.

Human Health Concerns and Risk Reduction

Echinococcus sp.:

In humans, infection with E. granulosus is called hydatid disease or cystic hydatid disease.
In humans, infection with E. multilocularis is called alveolar hydatid disease.
Humans can become infected when feces of infected carnivores OR carnivore pelts that are contaminated with feces are handled, or from environments contaminated with dog feces.
E. granulosus infection in the lungs of humans may be associated with fever and difficulty breathing.
E. granulosus cysts may also develop in other organs including the brain and cause severe problems because of the pressure on normal tissue.
E. multilocularis behaves like an invasive cancer and can cause liver damage resulting in abdominal pain and jaundice – in areas where this parasite is common, 70% of untreated cases become fatal within 5 years.
Human infections can be treated with antiparasitic drugs or through surgical removal of cysts.
Domestic dogs can serve as reservoirs for Echinococcus infection within communities.
Domestic dogs should not be fed carcasses or allowed to scavenge from infected game mammals as this perpetuates the cycle of infection.
Tapeworm infection in dogs and cats can be treated with anthelmintics (drugs used against tapeworms).

RISK REDUCTION:
Always wear rubber gloves when handling carnivore pelts, droppings or intestines.
Careful personal and food hygiene when in close proximity to dogs is crucial in preventing human infection.
Eggs dry out easily and can die within 2 hours in direct sunlight – survival time is increased in damp areas such as water holes.
DO NOT FEED TISSUES CONTAINING cysts TO DOGS.

Taenia ovis krabbei:

Taenia ovis krabbei is not transmissible to humans.

Samples for Diagnosis

Tapeworm infection can be verified on the basis of finding eggs in the fecal material of infected carnivores.
Cystic larval stages can be identified in intermediate hosts on the basis of gross appearance.
Human infection can be verified by taking X-rays, CT scans, and through a variety of immunological tests.
Portions of tissues containing cysts can be sent to appropriate diagnostic laboratories.