Distribution and genetic diversity of Haemaphysalis spp. (Ixodida: Ixodidae) in the islands of the Russian Far East

Despite the great epidemiological significance of Haemaphysalis spp., their distribution and genetic diversity in the Russian Far East, particularly on geographically isolated islands, remain poorly studied. To address this knowledge gap, questing ticks were collected from four islands in Primorsky Territory (Russia), which are located in Peter the Great Bay of the Sea of Japan, in 2019-2023. Ixodid ticks of the genera Haemaphysalis, Ixodes and Dermacentor were detected on the islands in varying proportions. Haemaphysalis longicornis Neumann and H. japonica Warburton predominated on Askold Island, D. silvarum Olenev and H. concinna Koch prevailed on Putyatin Island, whereas Ixodes spp. dominated on Russky and Popov islands. Haemaphysalis spp. were identified both morphologically and genetically and characterized using the cox1 gene and ITS2 locus. Haemaphysalis concinna and H. japonica were found on three and four islands, respectively; H. longicornis was detected only on Askold Island; and a single H. flava Neumann was collected on Russky Island. Notably, six Haemaphysalis females from Askold Island, genetically identified as H. japonica, exhibited morphological features intermediate between H. japonica and H. flava, indicating significant morphological polymorphism within H. japonica females. Based on cox1 gene sequence analysis, 11 haplotypes of H. japonica, 10 haplotypes of H. concinna and 7 haplotypes of H. longicornis were identified among ticks from islands, with 19 of these being novel. Phylogenetic analysis of the cox1 gene showed that the examined H. longicornis belong to a parthenogenetic lineage. At the ITS2 locus, we identified five H. japonica and four H. longicornis haplotypes, six of which were novel. ITS2 fragments of H. concinna were sequenced for the first time in this study and proved to be highly conserved. The cox1 and ITS2 sequences obtained from the single H. flava were identical to those from China and Japan, respectively. Phylogenetic analyses of cox1 and ITS2 sequences showed that Haemaphysalis spp. samples from different geographic locations do not form distinct clusters, suggesting that the genetic structure of these species is not geographically segregated. This study provides the first genetic characterization of Haemaphysalis spp. from islands in the Russian Far East, significantly expanding our knowledge of their occurrence and genetic diversity in the region.