New records of soft ticks (Acari: Argasidae) in the Caatinga biome of Brazil, with a phylogenetic analysis of argasids using the nuclear Histone 3 (H3) gene.

In Brazil, 19 species of the genus Ornithodoros (Acari: Argasidae) have been reported. The medical and veterinary importance of Ornithodoros ticks has increased substantially in recent decades, with the discovery of various relapsing fever Borrelia infecting Ornithodoros ticks. Herein, argasid ticks were collected during 2019-2020 from caves, abandoned nests and homes in various regions of Ceará State, Brazilian semiarid-Caatinga biome. In total, 289 ticks were collected and identified into five species: Ornithodoros cavernicolous (176 specimens), Ornithodoros fonsecai (81), Ornithodoros mimon (12), Ornithodoros rietcorreai (4), and a fifth species provisionally retained as Ornithodoros sp. Ubajara. Tick identifications were corroborated by a phylogenetic analysis inferred using the 16S rRNA gene. To extend the molecular characterization, DNA samples were tested by an additional PCR assay targeting the nuclear Histone 3 (H3) gene. Because there were no H3 sequences of argasids in GenBank, we extended this PCR assay for additional Ornithodoros species, available in our laboratory. In total, 15 partial sequences of the H3 gene were generated for 10 Ornithodoros species, showing 0% intraspecific polymorphism, and 1.5-11.6% interspecific polymorphism. Phylogenetic analyses inferred segregated Ornithodoros sp. Ubajara as a potential novel species. Our results also highlight the potential of the H3 gene for deeper phylogenetic analyses of argasids. The present study provides new data for argasid ticks of the genus Ornithodoros in the Caatinga biome. Because some of these tick species are human-biting ticks, active surveillance for the incidence of human infection due to Ornithodoros-borne agents is imperative in the Caatinga biome.