Echinococcosis (Dog Tapeworm Infection)
Echinococcosis is caused by the dog tapeworms Echinococcus granulosus and Echinococcus multilocularis. In people, the tapeworms can cause fluid-filled cysts or masses to form in the liver or other organs.
People are usually infected when they accidentally consume soil, water, or food that has been contaminated by Echinococcus eggs passed in dog stool.
Cysts form in the liver, lungs, or another organ and cause various symptoms, including pain.
Doctors do imaging tests (such as ultrasonography or computed tomography) to check for cysts, blood tests to check for antibodies to the tapeworm, and analysis of fluid from the cyst to confirm the diagnosis.
Treatment usually involves removing or draining the cysts and giving the drug albendazole.
Adult tapeworms of Echinococcus granulosus and Echinococcus multilocularis live in the intestine of dogs or other canines (such as foxes or coyotes). These tapeworms sometimes infect people, causing cysts in the liver or other organs.
Echinococcus granulosus is common in the sheep-raising areas of the Mediterranean, Middle East, Australia, New Zealand, South Africa, and South America. It also occurs in some parts of Canada, Alaska, and California.
Echinococcus multilocularis occurs mainly in Central Europe, Alaska, Canada, and Siberia. It also occurs in Wyoming, the Dakotas, and the upper Midwest.
Dogs, particularly herd dogs, become infected when they consume cysts of the tapeworms in tissues of infected animals (such as sheep, goats, cattle, or pigs). The cysts (called hydatid cysts) develop into adult tapeworms in the dog's intestine. Infected dogs pass tapeworm eggs in their stool. Sheep, cattle, goats, or pigs consume tapeworm eggs in soil contaminated with dog stool. Inside these animals, the eggs hatch and develop into cysts in the animal's internal organs.
People (often shepherds) are infected when they accidentally consume soil, water, or food that has been contaminated by Echinococcus eggs passed in dog stool.
Echinococcus eggs remain alive in soil for up to a year. Eggs may also be present on the fur of infected animals. After people touch an infected animal, they may pick up eggs, transfer the eggs from their hands to their mouth or to food, and thus become infected.
The eggs hatch in the intestine and release spheres that contain tapeworm larvae (called oncospheres). The spheres penetrate the wall of the intestine and travel through the bloodstream to various organs, such as the liver and lungs. In these organs, the spheres develop into cysts, which enlarge gradually and which, in people, can cause symptoms. The resulting infection is called echinococcosis.
Echinococcosis symptoms include the following:
Echinococcosis cysts in the lungs are usually discovered when a routine x-ray is taken. Cysts in the liver or other tissues can be seen using ultrasonography, computed tomography (CT) or magnetic resonance imaging (MRI).
Blood tests for antibodies to Echinococcusmay also be helpful. Antibodies are proteins produced by the immune system to help defend the body against attack, including that by parasites.
Doctors can often surgically remove the cyst or drain the cyst with a needle. To drain the cyst, they use ultrasonography to guide placement of the needle. They then remove cyst fluid, inject a salt solution into the cyst to kill the parasites, and drain the solution out. Masses due to Echinococcus multilocularis are removed surgically.
Albendazole is given before and during procedures, such as surgery or drainage of a cyst with a needle, to prevent the infection from spreading if the cyst's contents spill during the procedure. Albendazole is usually continued for 1 to 6 months after the procedure. It reduces the likelihood that a cyst will come back or spread. Albendazole alone can kill some cysts. It is also used to suppress the growth of cysts that cannot be removed surgically or drained.
Occasionally, when the infection is severe, liver transplantation is done.