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The ecology of West Nile virus (WNV) is complex, making it a prime example of the One Health approach. The transmission of WNV to humans depends on multiple factors, such as the presence of amplifying avian hosts and competent mosquito vectors. The abundance of the latter is influenced by land cover, temperature and climate. WNV lineage 2 has been endemic in Europe since around 2004, in Germany since 2018 with recurrent seasonal outbreaks. Endemic areas appear to be relatively stable, such as the Emilia-Romagna region in north-eastern Italy, Macedonia in central Greece and Saxony in eastern Germany. WNV sequences from affected regions are typically monophyletic, indicating regional maintenance. However, there is little knowledge on WNV dispersal and maintenance on a small spatial scale. WNV is maintained in mosquitoes over seasons, but due to a lack of genomic surveillance, it is not known whether this leads to localized persistence of WNV and how endemic virus variants disperse. In this study, we combined field sampling of adult mosquitoes at a small spatial scale over two seasons with WNV genome analyses, including testing of 15,672 mosquitoes of the genus Culex and sequencing of 18 WNV genomes from individual specimens. This study represents a first approach to regional mosquito-based WNV genomic surveillance in rural areas of the WNV endemic area in eastern Germany. Our results show that WNV is present at several sites both within and between two consecutive years with infection rates of up to 0.9 %. WNV sequences fall within the Eastern German clade in phylogenetic analyses but were highly diversified. Surprisingly, genetically different variants were found at same sites, and, in a few cases, genetically more similar variants were found at different sites. These findings suggest that there is extensive dispersal of variants in the region with limited evidence for localized amplification and persistence. We found statistical support for virus dispersal between two sites that are located along a direct local road connection. Understanding WNV ecology at small spatial scales is crucial to identify patterns of virus maintenance, dispersal and areas with higher WNV abundance rates, and to implement tailored prevention strategies to improve public health.
Patzina-Mehling et al. (Thu,) studied this question.