Surveillance of tick-borne encephalitis virus and Tribeč Virus in Ixodes ricinus ticks from Slovakia

Tick-borne viruses represent a significant and growing public health concern in Europe. This study investigated the minimum infection rates (MIRs) of tick-borne encephalitis virus (TBEV) and Tribeč virus (TRBV) in Ixodes ricinus ticks collected in Slovakia during 2016-2017 and 2023-2024. A total of 3,686 ticks (3,262 nymphs in 359 pools and 424 adults in 99 pools) from 13 sampling sites were screened for viral RNA. The overall MIRs were 0.38% for TBEV and 0.22% for TRBV. All positive detections occurred in nymphal pools. TBEV was detected at 8 of 13 sampling sites, with local prevalence ranging from 0 to 1.32%, whereas TRBV was detected at 6 sites, with local prevalence ranging from 0 to 0.83%. Two nymphal pools were positive for both TBEV and TRBV. Regression analysis indicated a statistically significant positive association between TBEV and TRBV positivity at the pool level. Genetic analysis of the nucleotide sequences obtained for segments 2 and 4 revealed a close evolutionary relationship among the Slovak TRBV strains. These findings suggest possible co-circulation of TBEV and TRBV in I. ricinus populations in selected sites in Slovakia and raise the possibility of co-infections, highlighting the importance of continued surveillance of tick-borne viruses.