Echinococcosis

This refers to infection with the tapeworm of the genus Echinococcus. Depending on the species two forms of the disease occur, Cystic Echinococcosis (caused by Echinococcus granulosus) and Alveolar Echinococcosis (caused by Echinococcus multilocularis). Infection is usually caused by ingestion of soil or water that has been contaminated with the eggs of the tapeworm. Dogs are definitive hosts for Echinococcus granulosus whilst dogs, foxes and coyotes for Echinococcus multilocularis. Sheep and cattle are intermediate hosts for Echinococcus granulosus from which dogs get infected when eating their organs. Rodents are intermediate hosts for Echinococcus multilocularis.

Incubation Period
5-15 years. Longer for Echinococcus multilocularis.

Transmission
This is usually caused by ingestion of the parasite’s eggs in contaminated soil or water. In Cystic Echinococcosis cysts develop containing the larval parasites (hydatid cysts) typically in the liver but also in lungs, bone, central nervous system and heart. In Alveolar Echinococcosis the larval parasites form vesicles that invade the surrounding tissues usually, liver, lung and brain. It is a much more serious disease and has a mortality of 50 – 75%.

Signs and Symptoms
These depend on the type, the location and size of the cysts. Cyst rupture, usually following trauma, may cause various degrees of anaphylaxis. In Cystic Echinococcosis patients may be asymptomatic for years until a certain size is reached to cause malaise, nausea, vomiting and discomfort. Characterized by liver parasitic tumours, in Alveolar Echinococcosis, which may spread to other organs including the lung and brain, local spread causes pain, malaise, weight loss and discomfort. Liver failure and death may ensue. The high mortality rate is also due to the disease occurring in remote areas with poor healthcare.

Diagnosis and Treatment
Especially in areas where Echinococcus is endemic, the presence of cystic lesions especially in the liver as detected by CT, MRI and Ultrasound should alert to the possibility of Echinococcosis. Serological tests are used to confirm the diagnosis. Cystic Echinococcosis can be treated with chemotherapy, and percutaneous aspiration following the injection of chemicals, however surgery remains the best definitive treatment. Alveolar Echinococcosis is harder to treat and usually requires radical surgery and long term chemotherapy.

Prevention
These include measures to reduce stray dog populations, avoidance of home slaughtering of sheep and other animals, preventing dogs from feeding on rodents, avoidance of water possibly contaminated by dog faeces, and avoidance of contact with wild dogs, coyotes and foxes. Hand hygiene when handling dogs and animal carcasses is extremely important.