Orthobunyaviruses belong to one of the four genera in the Peribunyaviridae family and have a structurally simple virion, comprising of only four proteins, and a tripartite, negative-sense, single-stranded RNA genome. As for the others arboviruses, they are transmitted by blood-feeding arthropod vectors, most commonly mosquitos. The importance of studies on mosquitos in Slovenia remained unrecognized until lately. However, since the outbreak of Chikungunya virus in 2007 in Italy and emergence of tiger mosquito in Slovenia and its rapid spreading, our country is acknowledged as entry point for vector-borne diseases. Currently known orthobunyaviruses can have devastating effects either by causing disease symptoms in humans such as febrile illness (Bunyamwera virus), self-limited fever (Oropuche virus), haemorrhagic fever (Ngari virus) and encephalitis (La Crosse virus). Besides, there are some orthobunyaviruses known more to have a potential teratogenic effects, for instance Cache Valley virus.
The aim of this thesis was to test the frequency of orthobunyavirus infection in mosquitos, collected on 28 locations all across Slovenia during the years 2017, 2018 and 2019. We found out that out of 1344 tested groups of mosquitos 153 groups, representing 11.4%, contained orthobunyavirus-infected mosquitos. The majority of these are from 2019, when considerably more sampling was made. In addition, our purpose was to define the diversity of orthobunyaviruses, in relation to the year and place of collection or species of their arthropod host. With Sanger sequencing of conserved genomic regions in the L segment and comparison of obtained nucleotide sequences with GenBank database, we selected fifteen closely related sequences, belonging to genera Orthobunyavirus, Phasivirus and Goukovirus. All three of them used to belong to Bunyaviridae family, which was recently divided into separated families in the Bunyavirales order. Based on the phylogenetic analysis, we noticed genetic drift, because the samples from 2017 and 2018 generally formed separate clades. Furthermore, we confirmed the correlation between diversity of viruses and different sampling sites as well as different species of mosquitos, because there were four large groups visible in the phylogenetic tree, comprising of sequences obtained from mosquitos that were similar either in place of their collection or mosquito species.