First record of Haemaphysalis hystricis in Hokkaido Island, Japan: an update on the northernmost record.

The tick Haemaphysalis hystricis is believed to be a vector of several infectious diseases such as severe fever with thrombocytopenia syndrome and Japanese spotted fever. This tick species is distributed across many Asian countries, including Japan. Recently, the distribution of H. hystricis has been expanding northward, probably due to migratory birds and climate change. In Hokkaido, the northernmost island prefecture of Japan, we collected two adult H. hystricis ticks, one in 2021 and another in 2026, that were identified based on their morphological features and mitochondrial 16S rDNA and COI sequences. To our knowledge, this is the northernmost record of occurrence of this tick species. The fact that unfed adults were collected in July and August, following the arrival period of migratory birds from southern areas, implies that engorged nymphs carried by these birds molted into adults after arrival at Hokkaido. While the immediate establishment of a local population is unlikely under the current subarctic climate of Hokkaido, our findings highlight a potential risk for future colonization, especially under ongoing climate change. This study provides important insights into the distribution of H. hystricis, raising awareness of the northward range expansion of this medically important tick species.