Tick–small mammal relationships in urban and forest environments in Yamagata Prefecture, Japan: First confirmation of the establishment of southern tick species in northern Japan

Small mammals are prominent hosts for ticks that transmit various infectious diseases to humans and other animals. Despite the widespread presence of ticks and small mammals worldwide and the fact that climate change is a global phenomenon, tick–small mammal relationships and the potential expansion of southern tick species have been investigated only in limited regions. To understand the global risk of tick-borne diseases, examining tick–small mammal relationships in northern regions is essential. In Japan, several tick-borne diseases have emerged, and multiple studies have reported adult and nymphal stages of southern tick species in northern areas. However, whether these species have successfully established in the north can be determined only through the detection of larval stages. Therefore, we examined tick infestation in small mammals captured from forest and urban environments in Yamagata Prefecture, northern Japan. A total of 55 individuals representing seven species were captured across the forest and urban environments. The predominant small mammal in both environments was the large Japanese wood mouse ( Apodemus speciosus ). Ticks were recovered only from A. speciosus captured in the forest environment. Among the recovered ticks, 29 were Dermacentor bellulus larvae, 13 were D. bellulus nymphs, and 1 was an Ixodes ovatus nymph. These results provide the first verification of the establishment of the southern tick species D. bellulus in northern Japan, and indicate that A. speciosus serves as an immature host for D. bellulus in the forest environment. Future studies are required to clarify tick burden across seasons and years, as well as the potential effects of host traits. • Dermacentor bellulus larvae were found from Apodemus speciosus in northern Japan. • This is the first confirmation of the southern tick establishment in northern Japan. • Tick infestation on A. speciosus was found in forest but not in urban environments. • Future studies are needed to clarify tick-small mammal relationships in northern Japan.