Heterogeneity of West Nile virus genotype 1a in Italy, 2011.

West Nile virus (WNV) is currently circulating in several European countries and, over recent decades, concomitantly with enhanced surveillance studies and improved diagnostic capabilities, an increase in the geographical distribution and in the number of cases in Europe has been documented. In Italy in 2011, 14 human cases of WNV neuroinvasive infections due to lineage 1 strains were registered in several Italian regions. Here we report WNV partial sequences obtained from serum samples of two patients living in different regions of Italy (Veneto and Sardinia). Phylogenetic analysis, performed on a fragment (566 nt) of the envelope gene, showed that WNV strains circulating in Italy in 2011 belong to lineage 1a, but are different from lineage 1a strains isolated in 2008-2009.The data reported here are consistent with the hypothesis of multiple recent introductions of WNV lineage 1a strains into Italy.