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Echinococcosis is a zoonotic disease caused by Echinococcus spp. tapeworms. The definitive hosts, which include dogs, other canids, hyenas and cats, carry the adult tapeworms subclinically. Dogs are particularly important in zoonotic transmission due to their close relationships with humans. 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. Echinococcosis is a major public health problem in some countries, and it may be emerging or reemerging in some areas. Approximately 2-3 million human cases are thought to occur worldwide.
Cystic echinococcosis, the most common form of the disease in people and domesticated animals, is caused by Echinococcus granulosus sensu lato (E. granulosus s. l.). Because the larvae of this organism usually develop as discrete single cysts, it is the least severe and most treatable form. Nevertheless, large or multiple cysts may cause irreversible damage to organs, and the rupture or puncture of the cyst can seed multiple organs with larvae or cause anaphylactic reactions. Humans typically become symptomatic many years after infection. Most livestock are slaughtered before the cysts become large enough to cause clinical signs, but if their entrails are fed to dogs, it perpetuates the cycle. Animals that live long enough, such as horses, may become ill. In addition, cystic echinococcosis causes economic losses from the condemnation of internal organs at meat inspection. In some cases, it may also result in decreased meat and milk production or decreased value of the fleece due to debilitation.
Alveolar echinococcosis, caused by E multilocularis, is less common than cystic echinococcosis, but it is very serious and more difficult to treat. The larvae of this organism grow as multiple, budding cysts, which can infiltrate entire organs and disseminate to distant sites including the brain. As well as affecting people, alveolar echinococcosis is reported to cause serious disease in animal intermediate hosts including dogs. The occurrence of this organism in a wildlife cycle between foxes and small mammals makes it difficult to prevent. Polycystic echinococcosis, which is usually caused by Echinococcus vogeli in humans, is similar to alveolar echinococcosis in the growth of the larvae and its presence in wildlife hosts. Other Echinococcus species seem to be rare in people or domesticated animals, but may affect wildlife.