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Fox tapeworm – more than just an annoying parasite

Published on April 23, 2024

Do not eat berries straight from the bush: Every child knows this basic rule. Not only to protect yourself from poisoning. Infections with fox tapeworm can also be avoided in this way.

Fortunately, cases of fox tapeworm are rare. Ten to twenty cases are diagnosed in Switzerland every year. There is no obligation to report the infection, but it is known that more cases of fox tapeworm have been occurring in Europe since 2000. One reason for this is the rapidly growing fox population.

No problem for the fox

Foxes as end hosts are adapted to the fox tapeworm and can live with the parasite. The two species form a symbiosis. However, the fox tapeworm can infect small rodents as an intermediate host via the eggs excreted in fox excrement, so that fox tapeworm larvae multiply in their livers. This makes the small rodents sick and therefore easier prey for the fox. The larvae then grow into worms in the intestine, which produce eggs. This allows the fox tapeworm to multiply in the fox population. Humans are actually false hosts; however, an infestation with fox tapeworm can have serious consequences.

Wash picked fruit, berries and hands

Alveolar echinococcosis, as the disease is medically called, is transmitted by ingesting the tapeworm eggs excreted by the host, for example by eating berries and fallen fruit contaminated with eggs or wild garlic picked in the forest. Fox tapeworm eggs can also be transmitted via direct contact with an infected animal or indirectly via a dog that has rolled in feces. Thorough washing of hands and collected fruit and berries is therefore the best protection. If eggs of the fox tapeworm enter the small intestine of an infected person, larvae can develop there, which pass through the blood into the liver and rarely into other organs, where they form cysts. These grow tumor-like into the surrounding tissue and increasingly impair the function of the affected organ.

More cases, better therapy

The disease often remains undetected for a long time. Similar to a malignant tumor, the larval tissue infiltrates and damages the liver, more rarely the lungs or brain, where it forms many small vesicles. Eventually, the consequences of the organ damage become noticeable with pain or jaundice. The number of cases has been rising for several years, with 15 to 20 new patients being diagnosed at the USZ each year. "A cure can only be achieved through surgical removal. Unfortunately, this is often no longer possible due to the extent of the disease," explains Ansgar Deibel, senior physician at the Clinic for Gastroenterology and Hepatology. Then medication is used. "The prognosis for inoperable patients is much better today. Whereas 90 percent of these patients used to die within ten years, we have only had to regret three deaths in the last twenty years."