Abstract
BackgroundWest Nile virus (WNV) is endemic in southeastern Romania and, after the unprecedented urban epidemic in Bucharest in 1996 caused by lineage 1 WNV, cases of West Nile fever have been recorded every year. Furthermore, a new outbreak occurred in 2010, this time produced by a lineage 2 WNV belonging to the Eastern European clade (Volgograd 2007-like strain), which was detected in humans and mosquitoes in the following years.ResultsWe report here, for the first time, the emergence, in 2015, of lineage 2 WNV belonging to the monophyletic Central/Southern European group of strains which replaced in 2016, the previously endemized lineage 2 WNV Volgograd 2007-like strain in mosquito populations. The emerged WNV strain harbors H249P (NS3 protein) and I159T (E glycoprotein) substitutions, which have been previously associated in other studies with neurovirulence and efficient vector transmission.ConclusionsIn 2016, both early amplification of the emerged WNV and complete replacement in mosquito populations of the previously endemized WNV occurred in southeastern Romania. These events were associated with a significant outbreak of severe West Nile neuroinvasive disease in humans.
Highlights
West Nile virus (WNV) is endemic in southeastern Romania and, after the unprecedented urban epidemic in Bucharest in 1996 caused by lineage 1 WNV, cases of West Nile fever have been recorded every year
In 2015, WNV infected mosquitoes were first detected on July 9 and 17 in Bucharest and Tulcea, respectively, while in 2016 the first infected mosquitoes were detected on June 21 in Bucharest, and June 6 in Tulcea, revealing early virus amplification, which led to higher mosquito infection rates in the outbreak year
Despite the limited resolution of Nonstructural protein 5 (NS5) fragment used for inferring phylogeny, the analysis showed that all the isolates of the newly detected virus in southeastern Romania form a cluster, which does not include the WNV derived from the patient in Sibiu, central Romania (Table 1, Fig. 2)
Summary
West Nile virus (WNV) is endemic in southeastern Romania and, after the unprecedented urban epidemic in Bucharest in 1996 caused by lineage 1 WNV, cases of West Nile fever have been recorded every year. A new outbreak occurred in 2010, this time produced by a lineage 2 WNV belonging to the Eastern European clade (Volgograd 2007-like strain), which was detected in humans and mosquitoes in the following years. We report, for the first time, detection in Romania, in 2015, of a lineage 2 WNV, belonging to the Central/Southern European monophyletic group of strains [7, 8], co-circulating with previously endemized lineage 2 virus (Volgograd 2007-like strain), and the replacement of the latter by the emerged WNV, in 2016, when a significant outbreak occurred.
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