Detection and Characterization of Sindbis Virus Genotype IV in Mosquitoes From Slovenia

Mosquitoes play a crucial role as vectors of disease pathogens and are among the most socioeconomically important animals in the world. Medically important arboviruses include the Sindbis virus (SINV), which causes chills, skin rashes, and joint pain. Endemic in northern Europe, SINV has been increasingly detected in central Europe. The main objectives of this study were to monitor and screen mosquitoes for the presence of SINV. We included samples of mosquitoes collected throughout the years at different locations in Slovenia. The mosquitoes were first identified and then pooled according to species, sex, date of sampling, and location. Nucleic acid (NA) was isolated from these pools, and the target segment of the SINV genome was amplified using molecular methods. We performed detailed phylogenetic analyses of the SINV-positive mosquito pools. From 2020 to 2024, we monitored mosquitoes at 226 locations in Slovenia and collected 112,001 samples, which were identified and grouped into 11,595 pools. Using real-time reverse transcription polymerase chain reaction (RT-PCR), we found SINV RNA in five pools of Culex modestus mosquitoes collected in two regions of northeastern Slovenia in August 2022 and in July, August, and September 2024. The SINV discovered in Slovenia (SINV-SLO) was classified as Genotype IV. We designed a primer scheme for the whole-genome amplification of SINV based on the alignment of the available SINV-IV sequences and performed molecular characterization of the sequences. Our findings revealed that SINV-SLO is closely related to the SINV strains identified in Russia, Azerbaijan, and China. In Europe, it is Genotype I that is most frequently detected and causes epidemics, whereas Genotype IV, which was detected in Slovenia, has not yet been associated with disease outbreaks.