Echinococcosis, or Hydatid disease/ Hydatidosis, is an infection caused by tapeworms of the genus Echinococcus, a tiny tapeworm just a few millimetres long. At least nine species within Echinococcus have been identified or designed, which infect a wide range of domestic and wild animals. Echinococcosis is a zoonosis, a disease of animals that affects humans.
Like all tapeworms the life cycle involves two animals. A carnivore is the definitive host – where the adult worms live in the intestines – and almost any mammal, including humans, can be the intermediate host - where the worms form cysts in various organs especially liver and lungs.
The disease symptoms are caused by the cysts, which are slow growing fluid-filled structures that contain the larvae and are most often located in the liver or lungs. Called hydatid cysts, for E. granulosus, E. canadensis, E. multicularis, etc., they act like tumours that can disrupt the function of the organ where they are found, cause poor growth, reduced production of milk and meat, and rejection of organs at meat inspection. In humans the disease can be severe, occasionally fatal, and the treatment is lengthy and expensive. Echinococcus infection is benign in the intestine of the carnivorous definitive host.
Echinococcus infection is a disease listed in the OIE Terrestrial Animal Health Code and must be reported by Member Countries and Territories according to the OIE Code.
Echinococcosis is a serious zoonosis, with rates of human cystic echinococcosis infection ranging from less than 1 per 100,000 to more than 200 per 100,000 in certain rural populations where there is close contact with domestic dogs. Incidence of human alveolar echinococcosis is usually < 0.5 per 100,000 but may be >100 per 100,000 in certain communities (e.g. Tibetan herdsmen).
Laboratory workers, animal handlers, veterinarians, dog owners are all at higher risk of infection. Since the eggs are shed in the environment, they can contaminate fruits, vegetables or water, or can stick to the fur of an animal and be transferred on hands to the mouth.
In humans the cysts of E. granulosus usually develop in organs such as the liver or lungs, so the signs of disease are due to liver or lung deficiency. Rarely, cysts form in bones causing spontaneous fractures, or in the brain causing neurological signs. Cysts or lesions of E. multilocularis occur primarily in the liver and grow slowly but with eventual serious liver pathology and high risk of mortality if untreated. As well, the cysts occasionally rupture and cause severe allergic reactions in humans.
Treatment includes surgery to remove or drain cysts or liver resection and use of long term chemotherapy with parasiticides (e.g. albendazole, mebendazole) to kill larvae or prevent them from growing back after surgery.
Since the route of infection is hand to mouth, frequent hand washing constitutes an important preventative measure.
In the Asia and the Pacific region, E. granulosus is important in Mongolia while both E. granulosus and E. multilocularis are important in China [1, 3, 6, 8, 9, 12, 13, 14, 16]. As in much of the rest of the world, the G1 genotype of the parasite is responsible for most cases of cystic echinococcosis in Mongolia and China. E. multilocularis cases in humans and wildlife were also recorded in Japan [10, 11]. While not as prevalent as in East Asia, E. granulosus has been reported in several countries in South Asia . E. granulosus has been eradicated from New Zealand but remains endemic in Australia, especially down the Eastern seaboard .
Although less important, E. canadensis has been reported recently, within which all genotypes including G6, G7, G8 and G10 have been found to exist in humans, sheep, goats, cattle, camels, etc. [2~6].There was also an isolated report of E. ortleppi in human . E. shiquicus, which was first discovered in China in 2006, is often observed in wildlife in Qinghai Tibet Plateau, and transmitted mainly between pikas and Tibet foxes .
Further epidemiological investigations are needed to better understand the current situation of these countries.
For more information: Echinococcosis worldwide situation on WAHIS