Abstract
Urbanization influences not only free-living organisms, but also various pathogens, including those with limited visibility to humans. Although previous research on urban parasites has primarily focused on human-specific and zoonotic species, a comprehensive understanding of parasite ecology in urban settings requires attention to inconspicuous enzootic species. In this study, we investigated two flea species, Aenigmopsylla grodekovi and Ceratophyllus ( Monopsyllus ) indages indages , parasitizing Eurasian red squirrels Sciurus vulgaris orientis in and around Obihiro City, Hokkaido, Japan. These fleas, dislodged during the routine handling of host squirrels, were collected and quantified during spring and autumn surveys to assess seasonal and spatial patterns of infestation across urban and rural sites. Over the course of a four-year survey (2017–2020), 317 squirrels (168 males and 149 females) were examined, with 284 individuals of A. grodekovi and 214 of C. ( M. ) indages indages recovered. The former was rarely observed in spring but showed a pronounced increase in autumn, with rural areas exhibiting 14.06 times more dislodged individuals than urban areas, on average. In contrast, the latter was more prevalent in spring (2.50 times higher than in autumn) and displayed no consistent difference between urban and rural habitats. Our results revealed distinct dislodgement patterns in two flea species in response to habitat and seasonal variations, indicating species-specific responses to urbanization. While direct quantification of flea abundance remains ideal, the number of dislodged individuals may serve as a useful indicator for assessing the effect of urbanization on host-parasitic interactions and infrapopulation dynamics.