Tapeworm Taenia arctos Confirmed in Slovak Brown Bears for the First Time

A tapeworm species never before confirmed in Slovakia has now been documented in the country’s brown bears. Researchers examining the digestive tracts of 125 legally culled free-ranging brown bears collected across Slovakia between 2025 and 2026 found Taenia arctos, a cestode associated with ursids as definitive hosts, in 14 of the animals. The finding, reported in Parasites & Vectors, closes a notable gap in the known distribution of a parasite that has been recorded in brown bears across several parts of the Northern Hemisphere but had not previously been verified within Slovak borders.

The prevalence figure carries a degree of statistical uncertainty that the authors make explicit. Fourteen infected bears out of 125 examined corresponds to a prevalence of 11.2 percent, with a 95 percent confidence interval spanning 6.3 to 18.1 percent. In practical terms, the true prevalence in the sampled population could plausibly lie anywhere between roughly 6 and 18 percent, a wide band that reflects the modest number of infected animals detected.

Beyond the headline prevalence, the survey yielded a total of 52 cestode specimens from the infected bears. Intensity of infection, meaning the number of worms carried per infected animal, ranged from a single worm to as many as 16, with a median of 2. That median indicates that most infected bears harbored only a light burden of parasites, while a minority carried substantially heavier infections.

Morphology alone, however, is a notoriously unreliable guide in this particular branch of the tapeworm family tree. Taenia arctos belongs to a group of taeniid cestodes whose members are so similar in outward appearance that distinguishing them has long challenged parasitologists. To resolve the identity of the Slovak specimens, the researchers selected one cestode from each infected bear and amplified a DNA fragment encompassing the complete mitochondrial cytochrome c oxidase subunit 1 gene, known as cox1, using polymerase chain reaction. The amplicons were then sequenced by the Sanger method and compared against the reference cox1 sequence of T. arctos.

The molecular results confirmed the morphological suspicion. All 14 sequenced specimens matched T. arctos, establishing the species’ presence in Slovakia on genetic as well as anatomical grounds. The sequencing also revealed that the Slovak isolates carried two distinct cox1 haplotypes, meaning the mitochondrial barcode differed at one or more positions among the sampled worms. Two haplotypes within a small sample of 14 specimens hints at some degree of genetic variation in the local parasite population, though the study does not extend to a population genetic analysis of how these variants relate to T. arctos lineages elsewhere in the species’ range.

Perhaps the most intriguing contribution of the study lies in a fine anatomical detail rather than in the biogeographic record. The researchers observed large hair-like structures in the copulatory part of the vagina in all examined T. arctos specimens in which this feature could be evaluated. Crucially, the same structures were not observed in the available comparative material of Taenia krabbei, the most morphologically similar congener of T. arctos. The authors note that these structures have not been reported in published descriptions of T. krabbei, which supports their potential diagnostic utility as a character for separating the two species.

This distinction matters because T. krabbei and T. arctos occupy overlapping host and geographic territory across the Northern Hemisphere, and misidentification between them can distort both ecological and veterinary interpretations of survey data. A consistent, observable morphological feature that separates the two would give researchers a faster and cheaper alternative to molecular sequencing for routine identification, reserving genetic confirmation for ambiguous cases. The authors frame the hair-like vaginal structures as a potentially useful additional morphological character for distinguishing T. arctos from morphologically similar Taenia species more broadly, though confirming that utility would require examination of more material from both species.

The confirmation of T. arctos in Slovakia also fits into a broader picture of taeniid parasites circulating in European bear populations. Brown bears act as definitive hosts for these cestodes, harboring the adult worms in their intestines and shedding eggs into the environment. The species had been reported from brown bears in several parts of the Northern Hemisphere prior to this study, making its absence from the Slovak record more likely a gap in surveillance than a true absence of the parasite.

For wildlife managers and parasitologists monitoring the health of Central Europe’s growing bear population, the study adds a confirmed parasite to the national checklist and offers a practical morphological marker for future surveys. As the authors conclude, the study confirms the occurrence of T. arctos in brown bears from Slovakia based on both morphological and molecular evidence, and the consistently observed hair-like structures may prove a valuable addition to the taxonomist’s toolkit.

Subject of Research: First confirmation of the tapeworm Taenia arctos in brown bears from Slovakia using morphological and mitochondrial cox1 sequence evidence

Article Title: The occurrence of Taenia arctos (Cestoda: Taeniidae) in brown bears (Ursus arctos) from Slovakia: genetic variation and notes on morphological identification

Article References: Kuzmina, T. A., Molnár, L., Hurníková, Z., Greben, O., Königová, A., Fajth, R., & Syrota, Y. (2026). The occurrence of Taenia arctos (Cestoda: Taeniidae) in brown bears (Ursus arctos) from Slovakia: genetic variation and notes on morphological identification. Parasites & Vectors. https://doi.org/10.1186/s13071-026-07756-9

Image Credits: AI Generated

DOI: 10.1186/s13071-026-07756-9

Keywords: Taenia arctos, brown bear, Ursus arctos, Slovakia, tapeworm, prevalence, cox1, haplotypes, morphological identification, Taenia krabbei, parasitology, wildlife