Czech scientists report on first domestic case of parasite found in fish

Scientists in the Czech Republic have described the first domestic case of infection with a parasite.

Diphyllobothriasis (dibothriocephalosis) is caused by the human broad tapeworm Dibothriocephalus latus. The source of infection is fish consumption, such as pike and perch.

Except for a few imported infections, no cases of human diphyllobothriasis or of fish infected with parasite larvae have been reported in Central Europe, which includes the Czech Republic, Austria, Hungary, and Germany.

However, earlier this year, an autochthonous case of diphyllobothriasis caused by Dibothriocephalus latus was documented in the Czech Republic. Findings were reported in the journal Emerging Infectious Diseases.

A 37-year-old man, who had not traveled to known diphyllobothriasis-endemic areas or previously consumed raw or undercooked fish products, obtained a pike caught in October 2023 near Horní Planá, the largest settlement on the Lipno reservoir in South Bohemia. He consumed raw salted roe (caviar) from the pike, the most common source of diphyllobothriasis in many parts of Russia.

Two months later, he experienced occasional abdominal bloating. After another two months, he excreted part of the tapeworm. An examination confirmed the presence of Dibothriocephalus latus tapeworm eggs. Treatment with mebendazole was unsuccessful, but the tapeworm was later completely expelled after a single dose of praziquantel.

A tourist probably introduced Tapeworm.
The Lipno Reservoir is a popular tourist destination, attracting thousands of visitors annually, including local and foreign anglers. The reservoir has never been stocked with fish from abroad, such as pike, perch, or ruffe, so it is unlikely that the tapeworm was imported from diphyllobothriasis-endemic areas through fish. 

108 potential second intermediate hosts, including pike, perch, and ruffe, from the reservoir were examined in May and August 2024, but no signs of Dibothriocephalus latus were found.

Scientists said a plausible explanation for the domestic occurrence of Dibothriocephalus latus is the parasite’s recent appearance in this ecosystem, probably introduced by tourists from a diphyllobothriasis-endemic area, such as the lake regions of northwestern Russia, who released tapeworm eggs into the water or its surroundings via stool.

“We often see people succumbing to the fear of parasites or being frightened by the false campaigns of dishonest sellers of anti-parasite products. However, the concerns are completely unnecessary. There are very few human parasites in the Czech Republic,” said Tomáš Scholz, from the Institute of Parasitology, Biology Centre of the Czech Academy of Sciences.

Scholz added that the tapeworm’s occurrence in fish in Lipno is very rare, and the risk of infection in humans is very low because the larvae are destroyed during normal heat treatment or deep freezing of fish. Diphyllobothriasis is not a life-threatening disease, and there is an effective treatment.

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