Thelazia callipaeda in free-ranging brown bears (Ursus arctos) from Romania.

Thelazia callipaeda is a zoonotic spirurid nematode infecting the conjunctival sac of various mammalian hosts, including carnivores and humans. Although initially restricted to Asia, the parasite has expanded across Europe over the past two decades, with reports of infection in domestic and wild hosts as well as humans. In Romania, T. callipaeda has been documented in several wild carnivore species and lagomorphs, but not yet in brown bears (Ursus arctos), despite housing the largest European bear population. Between 2021 and 2025, the eyes of 25 brown bears legally hunted in different regions in Romania were inspected macroscopically and microscopically for the presence of eyeworms. When detected, nematodes were removed, morphologically identified, and molecularly confirmed by amplification and sequencing of the cox1 gene to confirm species identity. Thelazia callipaeda was detected in one brown bear (1/25, 4%) from Bihor County, with 17 nematodes (12 females, 5 males) retrieved from both eyes. BLAST analysis of the cox1 sequence revealed 100% identity with T. callipaeda haplotype 1. This study shows the first identification of T. callipaeda in Romanian brown bears, expanding the known host range of this zoonotic nematode.