The West Nile virus (WNV) belongs to the genus Orthoflaviviridae, which poses a significant global public health and economic burden because it is associated with major disease outbreaks in humans and animals. Climate change, which affects vectors, reservoirs, and incidental hosts, contributes to changes in the geographic distribution of WNV. In humans, WNV infections are mostly asymptomatic or present as a febrile illness with nonspecific symptoms; only a small percentage of those infected develop more severe neuroinvasive forms of the disease. WNV is transmitted by mosquitoes of the species Culex pipiens, and the virus circulates primarily among birds. When infected mosquitoes feed on other mammals, such as humans and horses, they can also transmit the virus to them. The virus has been circulating in Europe for decades, including in neighboring countries such as Italy and Serbia, as well as in South and North America, Australia, Africa, and Asia. The aim of this master’s thesis was to investigate the prevalence of WNV infections in patients with signs of central nervous system infection in Slovenia and to analyze the genetic and phylogenetic characteristics of Slovenian WNV. Using serological methods, we examined 803 samples from patients with signs of central nervous system infection between 2023 and 2024. We identified four positive samples, which we subsequently confirmed and characterized using molecular methods. We also included three samples from crows that died from WNV infection during the same period in our molecular analysis. We performed a phylogenetic analysis of the complete WNV genomes obtained from various samples and determined that WNV genotype 2 is responsible for the infections in Slovenia. We found that all Slovenian WNV sequences from 2024 are related to one another and are genetically most closely related to Italian sequences from the same year, which confirms the introduction of WNV into Slovenia during concurrent disease outbreaks in neighboring countries.
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