Cystic Echinococcosis and Multilocular Echinococcosis
Cystic Echinococcosis or Hydatidosis caused by Echinococcus Granulosus
Life cycle
The adult worm affects various final hosts such as domestic dogs and wild carnivores like foxes, coyotes, wolves and jackals. They spread the eggs with their faeces. Intermediate hosts are sheep, cattle, swine, goats, equines, camelids and cervids. They acquire the infection by ingestion of the infective eggs during grazing. Carnivores acquire the infection by ingestion of infected raw material of the intermediate hosts (mostly viscera). Like the intermediate hosts, man acquires the infection by ingestion of infective eggs.
Cystic Echinococcosis is mainly maintained in the dog-sheep-dog cycle. The infection is transmitted to dogs when they are feed infected viscera of sheep during the home-slaughter of sheep.
The eggs are found on the surface of faecal matter of dogs, and they can accumulate in the perianal region of dogs. The dog carries the eggs on tongue and snout to different parts of its body. Direct contact with dogs is an important mode of transmission to humans, as is consumption of vegetables and water contaminated with infected dog faeces. Humans are accidental intermediate hosts and are not able to transmit the disease.
Distribution
There are areas of high endemicity in southern South America, the Mediterranean coast, the southern part of the former USSR, the Middle East, south-western Asia, northern Africa, Australia, New Zealand, Kenya and Uganda. On the Tibetan Plateau for example, cysts have been found in 6.6% of the population. In southern Argentina 26.7 cases per 100,000 were found.
Control
Preventive measures depend on diminishing the infection rate in dogs by avoiding them to eat sheep viscera. This means ensuring sanitary conditions for local slaughtering. Other measures include personal hygiene, periodic treatment of dogs, meat inspection and avoiding ingestion of possibly infected raw vegetables and water.
Multilocular Echinococcosis caused by Echinococcus Multilocularis
Life cycle
The natural definite hosts are foxes, chiefly the arctic fox and the red fox. The intermediate hosts are wild rodents, who carry the infection in their liver. They acquire the infection by ingestion of the infective eggs spread in the faeces of infected foxes. Domestic dogs and cats may also serve as definitive hosts when they ingest infected wild rodents.
Humans can come into accidental contact with the eggs when handling dead foxes or drinking water from streams contaminated with the faeces of infected foxes. Domestic dogs and cats can carry the infection into the home when they hunt wild rodents.
Distribution
The distribution of E. multilocularis is limited to the northern hemisphere. In North America the parasite is present in sub arctic regions of Alaska and Canada and in a few northern states of the US. In Europe it is present in the central and eastern countries and in Asia in the former USSR, Turkey, Iraq, northern India, Japan and central China. In some regions of central Europe approximately 40-75% of the red fox populations are infected with E. multilocularis. On St. Lawrence Island, Alaska, up to 100% of the arctic foxes are infected. In Gansu, a province of China, 8.8% of the human population was found seropositive.