Georeferenced evidence of Haemaphysalis longicornis on the European continent: novel avian host records and questing ticks from the European side of Istanbul along a major flyway to Europe

Abstract Background Haemaphysalis longicornis Neumann, the Asian longhorned tick, is a highly invasive species of veterinary and public health importance. Although it has recently been reported from the European part of Türkiye, geographically explicit evidence from the European continent remains limited. We investigated the occurrence of Ha. longicornis on birds and in questing ticks from georeferenced localities on the European side of Istanbul, a major migratory bottleneck linking Türkiye with northeastern and central Europe. Methods Birds were examined for ticks during the 2025 spring and autumn migration seasons at a ringing station on the European side of Istanbul, and additional Haemaphysalis specimens were collected from nearby vegetation. Ticks were identified morphologically and confirmed by COI-based molecular analysis. Seasonal prevalence was compared using Fisher’s exact test, a two-sample test for equality of proportions, and binomial generalized linear models accounting for host species. Results Haemaphysalis ticks were recorded from 46 birds representing 17 host species. Across these host species, 4816 birds were examined, and 108 Haemaphysalis specimens were recovered, comprising 95 Ha. longicornis larvae, 6 Ha. longicornis nymphs, and 7 Ha. punctata nymphs. No adult Haemaphysalis were found on birds. All avian host species from which Ha. longicornis was detected represented novel host associations. Four of six engorged larvae moulted successfully to the nymphal stage. COI sequence data from pooled Haemaphysalis samples were consistent with identification as Ha. longicornis, and representative sequences clustered within the Ha. longicornis clade. Three questing nymphs collected by trial flagging were morphologically indistinguishable from COI-confirmed Ha. longicornis nymphs. Pooled seasonal prevalence was higher in autumn than in spring, although unadjusted comparisons were not significant; after accounting for host species, autumn showed higher estimated odds of infestation. Conclusions These findings provide geographically explicit evidence of Ha. longicornis on the European continent. Detection on multiple bird hosts, together with recovery of questing specimens from the local environment, suggests that Ha. longicornis is not only transported by birds but may also be locally established on the European side of Istanbul. Our findings highlight the ecological and epidemiological relevance of wild birds and migratory corridors in the transport and potential establishment of invasive ticks in Europe.