Cystic echinococcosis (hydatid disease) is a parasitic disease that affects both humans and mammals, more commonly dogs, horses, sheep and rodents. Both cystic and alveolar echinococcosis develop when humans ingest eggs of Echinococcus granulosus or E. multilocularis which are shed in the faeces of dogs harbouring adult stages of these tapeworms.
Echinococcosis has a global distribution and causes serious morbidity and death if left untreated.
Cystic echinococcosis is principally maintained in a dog–sheep–dog cycle. Human cystic echinococcosis (or hydatidosis) is a disease caused by the larval stages of the dog tapeworm E. granulosus (Cestoda).
The infection is transmitted to dogs when they are fed infected viscera of sheep or other ruminants during the home-slaughter of animals. Dogs also become infected through scavenging.
Direct contact with dogs and consuming vegetables and water contaminated with infected dog faeces are important modes of transmission to humans.
Humans are accidental intermediate hosts and are not able to transmit the disease. There are areas of high endemicity in southern South America, the Mediterranean coast, the southern part of the former Soviet Union, the Middle East, south-western Asia, northern Africa, Australia, Kenya, New Zealand and Uganda.
In its domestic transmission cycle, dogs are definitive hosts of the adult tapeworm, and ruminants (particularly sheep and goats) are intermediate hosts.
Humans become accidental intermediate hosts following ingestion of eggs through direct contact with definitive hosts or indirectly through food, water or soil contaminated with eggs. The larval stage that emerges from the egg gives rise to a hydatid cyst.
A cyst slowly enlarges, and signs and symptoms of disease vary according to its location and size in the body, duration of the development of the cyst, and the cyst type. Cases of infection with more than one cyst occur. Cysts are found mostly in the liver and lungs, although other organs may be affected.
Prevention, control and treatment
Cystic echinococcosis, a chronic disease with an asymptomatic period of several years. It is difficult to diagnose without imaging tools (such as computed tomography or ultrasound) and laboratory confirmation of the disease relies on good serological tests.
Treatment comprises mainly surgical intervention or percutaneous treatment and/or high dose, long-term therapy with albendazole alone or in combination with praziquantel.
Surveillance in animals is difficult because the infection is asymptomatic in livestock and dogs, and is not recognized or prioritized by communities or local veterinary services.