Alveolar hydatid disease (AHD) is a form of echinococcosis, or a disease that originates from a parasitic flatworm. AHD is caused by an infection of the flatworm species Echinococcus multilocularis. Although alveolar echinococcosis is rarely diagnosed in humans and is not as widespread as cystic echinococcosis (caused by Echinococcus granulosus), it is also still a serious disease that has a significantly high fatality rate. It is considered one of the most life-threatening helminthic infections humans can have.
Signs and symptoms
As the larvae grow in the liver, they create lesions.
Cause
AHD is caused by the larval stage of E. mulitilocularis, a species of flatworm found in the Northern Hemisphere. Their feces then will contain the worms' eggs, which have fully developed larval worms inside.
Pathophysiology
Once ingested by humans, "the oncospheres hatch in the stomach or small intestine, become activated, penetrate the epithelial layer, and migrate via blood and lymphatic vessels to the visceral organs, primarily the liver, where they develop to another larval stage, the metacestode." Chemotherapy must continue for many years, sometimes for the remainder of the patient's life. Failure to comply with these expensive and difficult treatments will likely result in death for the patient. The growth happens slow, and so many people do not get symptoms until the later stages.
Epidemiology
AHD is not as common as diseases caused by other flatworms, but it is still prevalent in the Northern hemisphere. It is not uncommon in China, with some communities having a 5% or more infection rate. In Europe, it is considered an emerging disease.
History
In 1855, Rudolf Virchow, the German pathologist, recognized that the disorder that was at the time known as colloid carcinoma of the liver, which was known for its tumor-like lesions in the liver, were actually caused by an Echinococcus species. For the next 100 years, it was debated whether the species was E. granulosus or a different species. It was finally settled by two publications between 1954 and 1955, the former from Alaska and the latter from Germany.
Research directions
Wildlife research is working to detect the parasite in new areas.