Detection of a novel Francisella in Dermacentor reticulatus: a need for careful evaluation of PCR-based identification of Francisella tularensis in Eurasian ticks.

Francisella tularensis, the causative agent of tularemia, has been detected in ixodid ticks in some regions of North America, Europe, and Asia. In the present study, 245 Dermacentor reticulatus, 211 Ixodes ricinus, and 194 Haemaphysalis concinna adults from Hungary were tested for the presence of F. tularensis by polymerase chain reaction (PCR) assays based on 16S ribosomal RNA (16S rDNA) and T-cell epitope of a Francisella membrane protein (TUL4). No Francisella-specific amplification products were detected in I. ricinus and H. concinna ticks. Francisella DNA was identified using PCR assays based on 16S rDNA and TUL4 gene in D. reticulatus with similar prevalence (minimum 1.2%) as demonstrated in earlier European and Asian studies detecting F. tularensis in D. reticulatus. However, the 16S rDNA and TUL4 gene sequences of the Francisella-like agent occurring in D. reticulatus differed from the homologous sequences of Francisella spp. deposited in GenBank. Phylogenetic reconstructions showed that the new genotype detected in D. reticulatus was closely related to Francisella-like endosymbionts of North American Dermacentor ticks. Although further studies are needed on the relationship of this bacterium with ticks, the results highlight the need for careful evaluation of PCR-based identification in European and Asian laboratories that screen ixodid ticks for F. tularensis.