Ants Tull, Egle Tammeleht, Harri Valdmann, Maris Hindrikson, Urmas Saarma

The brown bear is a flagship species in the ecosystems of Eastern and Northern Europe, but little is known about its parasitofauna in the Scandinavian-Baltic region. As an omnivore, the brown bear can acquire parasites from animal intermediate hosts, soil and plant material, which can lead to a more diverse parasite community. However, the hibernation-induced physiological changes can challenge parasite overwintering survival. As some parasites can be detrimental to the bear’s condition and present a threat of zoonotic spillover infections for humans, parasite monitoring is essential under the One Health framework.
This study provides the first analysis of brown bear scats in Estonia, revealing one of the highest prevalences of parasites in bear scats in Europe (FO=78%), and the seasonal and interannual infection dynamics. For this, bear scats were collected for three years, and based on genetic host identification, 378 scat samples were selected for further analyses. Parasite eggs and oocysts were identified based on morphology. The prevalence of parasites increased from 2022 to 2024, and nematodes were the most prevalent (62%), followed by cestodes (20%), protozoa (15%), trematodes (7%) and acanthocephalans (2%). The bear-specific nematode Baylisascaris transfuga had the highest prevalence (54%). Most parasite taxa were zoonotic and thus potentially hazardous to humans. Varying seasonal dynamics hinted at transmission routes, and opposing dynamics were revealed for protozoa and nematodes, with nematodes being most prevalent in fall and protozoa in spring. Coinfection analyses via JSDM pointed to cestodes being central to parasite community structure. The study will introduce the results of this research and compare the findings with those from studies done in Central and Southern European countries.