GENERAL CHARACTERISTICS
Although rarely found in the brain of humans, E. multilocularis causes alveolar hydatid disease, which is a fatal form of echinococcosis. It is the most lethal of all helmintic diseases. The cyst is extremely dangerous because it lacks a laminated membrane and develops a series of connected chambers. The chambers contain little or no fluid and rarely contain a scolex. The morphology of the cyst is very similar to that of E. granulosus, but the adult organisms are much smaller (1.2 to 3.7 mm). The cysts are very resistant to cold temperatures.
EPIDEMIOLOGY
E. multilocularis is found in Asia, Europe, and northern North America, including areas such as Alaska, Montana, and Minnesota. Foxes, coyotes, and dogs are the definitive host for E. multilocularis, whereas rodents are the intermediate host. The parasite is occasionally transmit ted to humans through the ingestion of contaminated food or water, and by handling infected animals. Fur trappers and veterinarians are at an increased risk of infection as a result of exposure to infected animals. The life cycle of E. multilocularis is essentially identical to that of Echinococcus granulsosus.
PATHOGENESIS AND SPECTRUM OF DISEASE
Alveolar hydatid disease is a highly lethal, destructive disease. The cyst of E. multilocularis grows slowly and may take years to produce clinical symptoms. Many cysts are asymptomatic during the life of the infected individual and are sometimes found during autopsy, surgery, or imaging scans related to other clinical conditions. The severity of symptoms depends on the location of the cyst and the size, as seen with E. granulosus. Cysts form primarily in the liver and metastasize to the lung or brain. Cysts in the liver are not restricted with a laminated cyst wall and are capable of expansion into a multicystic structure. This multilocular (many chambers) hydatid cyst is often mistaken for a hepatic sarcoma, making diagnosis difficult. This disease is often fatal.
LABORATORY DIAGNOSIS
Ultrasound, CT scans, and MRI are used to visualize the cyst and can be supported with serologic testing. Sero logic tests, such as ELISA, are sensitive and highly specific.
THERAPY
The most common treatment is to remove the parasite surgically; however, the disease is usually diagnosed late, when it is inoperable and results in a high rate of fatality. Treatment with mebendazole and albendazole has been used successfully and may be the preferred treatment in many cases. Surgery should follow and is the only means of removing the cyst.
PREVENTION
Controlling rodents is an important means of prevention along with educating the public at risk to avoid exposure to infective feces. Practicing good hygiene and periodically deworming household pets are also helpful.
