Survey of filarial infection in Japanese black bears (<i>Ursus thibetanus japonicus</i>) around Lake Towada area

In this study, we examined filarial infections in Japanese black bears around the Lake Towada area from 2020 to 2022. Microfilariae were observed in 81.6% of blood smears. Consistent with previous findings in Iwate Prefecture, polymerase chain reaction (PCR) analysis detected Dirofilaria ursi (89.7%) and Mansonella sp. (66.7%) in extracted blood DNA. The body size of D. ursi microfilariae matched previous reports, whereas Mansonella sp. microfilariae were smaller than those of D. ursi and other known species. Although we attempted to identify Mansonella sp. adult filariae using PCR, all recovered adults were D. ursi; no adult Mansonella sp. were detected. Further studies are needed to better identify and understand both the adult filariae and microfilariae of Mansonella sp. in Japanese black bears.