Infection status of Baylisascaris transfuga in captive Asiatic black bears (Ursus thibetanus) from three bile farms in South Korea, with molecular analyses

Bears harbor various endoparasites that pose risks to humans and other animals. However, information on parasitic infections in Asiatic black bears in South Korea (Korea) is limited, and potential hazards still exist because of the close contact between bears and humans on bile farms. The present study was conducted to assess the gastrointestinal parasite infection status in captive Asiatic black bears (Ursus thibetanus) at bile farms in Korea. Additionally, we aimed to characterize the molecular aspects of Baylisascaris transfuga (Nematoda: Ascarididae), the sole species investigated throughout the study. Fecal examinations were performed on a total of 84 fecal samples collected from three bear farms in Hwacheon-gun (gun = County) and Donghae-si (si = City), Gangwon-do (do = Province), and Dangjin-si, Chungcheongnam-do. Eggs were identified morphologically, and an adult worm expelled in the feces was analyzed molecularly using the partial cytochrome c oxidase subunit 1 and 2 (cox1 and cox2) gene markers. The prevalence of helminthic eggs was 10.7 %, identified as B. transfuga based on morphological characteristics. The eggs, which were oval and brown with thick shells, had a mean length of 87.3 ± 8.9 μm on the long axis and 70.7 ± 6.1 μm on the short axis (n = 30). An adult female roundworm found in the feces of one individual, measuring 27 cm in length and 0.4 cm in width, was also identified as same species through genetic methods. Herein, we described the prevalence of B. transfuga in captive bears in Korea and its molecular characteristics for the first time. Additionally, we reviewed the sequences of the genus Baylisascaris available in the International Nucleotide Sequence Database Collection, noting that many of these sequences often have ambiguous or potentially incorrect identifications, complicating the understanding of their phylogenetic status. This investigation is part of disease screening efforts aimed at enhancing the welfare of captive bears prior to their imminent relocation to sanctuaries. Health monitoring and endoparasite control in farmed bears should be carried out in both veterinary and public health contexts.