Jet set pets: examining the zoonosis risk in animal import and travel across the European Union

Fooks, Anthony R; Johnson, Nicholas

Echinococcosis results from infection with the larval stages of cestodes belonging to the genus Echinococcus. 37 Two species are commonly associated with disease in humans, ie, E. granulosus, which is found worldwide, and E. multilocularis, which has a restricted distribution and causes alveolar echinococcosis. E. multilocularis is found in the northern hemisphere in parts of Western Europe, Asia, and North America, particularly the western coastal regions of Alaska. The species belongs to the family Taeniidae. It exists in a two-host life cycle, parasitizing wild canids such as the red fox as definitive hosts of the adult form and prey species, which act as an intermediate host for the larval stage. Intermediate hosts include species such as the bank vole (Myodes glareolus) and field vole (Microtus agrestis). Adult tapeworms, 2-4 mm in length, develop in the small intestine of the definitive host, and then shed eggs persistently for up to 5 months. The eggs contaminate the environment and are resistant to desiccation and low temperatures. 38 This enables egg survival for extended periods. Intermediate hosts ingest the eggs which hatch in the intestine to release metacestodes. These attach to the intestinal wall, cross it, and then migrate from the intestine via the bloodstream to organs such as the liver where they form hydatid cysts into which protoscoleces bud. Upon ingestion of the intermediate host by a fox, the protoscoleces develop into an adult stage, enabling attachment to the intestinal wall and the life cycle is complete. All mammals can develop alveolar cysts following ingestion of eggs, and these continue to develop to the extent that infected organs, particularly the liver and lungs, are destroyed and the host dies. Treatment in humans is limited to surgery to excise cysts, although this carries risks if the cyst bursts, leading to metastases that cause further cysts, or pharmacological therapy with albendazole. 39 Within endemic areas, human contact is limited to those having a close association with animals, such as hunters. However, dogs can act as a definitive host and contaminate areas where humans may come into contact with parasite eggs. Therefore, owning a dog can be considered a risk factor for infection with E. multilocularis in endemic regions.