Echinococcus multilocularis


Echinococcus multilocularis
Kingdom Animalia
Phylum Platyhelminthes
Class Cestoda
Sub-class Eucestoda
Order Cyclophyllidea
Family Taeniidae
Genus Echinococcus
Species E. multilocularis

Also known as: Dwarf fox tapeworm

Overview

Rat infected with E. multilocularis - Dr. I. Kagan

E. multilocularis is not present in the UK but is endemic in central Europe and North America. It is zoonotic and so presents a major health problem in Europe (including Switzerland where urban foxes are now infected) having spread from 4 countries in the 1980s to being found in 12 countries now. This has been attributed to the anti-rabies campaign which has increased the number of foxes which are commonly found as the definitive host. Humans can act as intermediate hosts if eggs are ingested causing the formation of hydatid cysts in the liver, these rapidly invade the liver and are inoperable.

Characteristics

E. mulitlocularis is a relatively small tapeworm between 2-4mm as an adult.
Scolex

  • 2 rows of hooks
  • 4 suckers

Proglottid

  • Between 3 - 5 segments in total
  • Terminal proglottid forms 1/2 the length of the mature worm
  • 1 proglottid shed per week
  • Has single genital pore

Eggs

  • 200-300 eggs per mature proglottid
  • 30-40μm in diameter
  • Striated shell
  • Hooks visible on oncosphere

Life Cylce

E. multilocularis has a typical cestode life cycle involving the formation of a metacestode cyst in the intermediate host before developing to adulthood in the definitive host. The definitive host for E. multilocularis is most commonly the dog, though it has also been seen in the cat. Epidemiologically the most important definitive host in the spread of the disease is the fox. E. multilocularis mainly uses small rodents such as voles, mice and rats as an intermediate host, forming multilobular hydatid cysts in the liver of the host. The short life span of the intermediate host species is the reason for the rapid growth of the cyst, even in longer lived host like humans. This is the stage that generally causes pathology in the host animal and can be fatal.

Epidemiology

E. mulitilocularis is found throughout the northern hemisphere, originally its primary range was the tundra of northern Russia and eastern Europe. The prevalence of this worm is increasing to encompass many urban areas which increases the risk of zoonotic infection. The parasites definitive host in the wild is the red fox and the arctic fox. In North America and Europe there is an increasing presence of red foxes in urban and suburban areas, this increases the risk of infection of both humans and pets. The disease it causes is called Alveolar Hydatid Disaese.

Treatment and Control

Control involves treatment of definitive hosts, dogs and cats, with anthelmintics in order to remove adult worms from the host. The treatment of intermediate host pets (and humans) is not routine and can be dangerous as due to the infiltrative nature of the hydatid cyst and its metastatic ability. Surgical removal of the cyst is therefore not advisable.


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