Summer collection of multiple southern species of ticks in a remote northern island in Japan and literature review of the distribution and avian hosts of ticks.

Expansion of ticks and tick-borne diseases is of increasing concern worldwide. To decrease the risk of ticks and tick-borne diseases to public health, understanding the mechanisms of their current distribution and future expansion is needed. Although tick distribution has been studied globally on continents and large islands that are inhabited by large mammals, less attention has been paid to remote islands. However, small islands are often important stopover sites for migratory birds that may contribute to long-distance dispersal of ticks. Therefore, islands would be a suitable system to rule out potential effects of mammals and to evaluate the contribution of birds to the expansion of ticks and tick-borne diseases. We collected questing ticks by dragging cloths over vegetation on Tobishima Island, northern Japan, in summer 2021, and conducted a literature search of the distribution and avian hosts of hard tick. We found several southern species of ticks (Haemaphysalis hystricis, H. formosensis, H. cornigera, Amblyomma testudinarium, and Dermacentor bellulus) on the island. These species have rarely or never been reported from the mainland of Japan at similar latitudes or higher, where large mammals are found. They are known vectors of tick-borne diseases, such as severe fever with thrombocytopenia syndrome. The present study suggests that migratory birds may contribute to the expansion of ticks and tick-borne diseases, and a remote island may function as a front line and/or a hub for their expansion. Evaluating tick fauna on remote islands used by migratory birds might be useful to monitor the expansion.