IgG and IgM levels against West Nile virus (WNV) were measured in 20,033 serum samples that were obtained between October 2008 to September 2009 from 9913 blood donors in the district of Ferrara, northeastern Italy. As confirmatory test, a microneutralization assay was used to detect the presence of neutralizing antibodies against WNV. Sixty-eight subjects (0.69%) were positive for anti-WNV by immunofluorescence assay. Large differences in the prevalence of antibodies to WNV were noted between towns in the area evaluated.

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The development and persistence of anti-West Nile Virus (WNV) immunoglobulin G (IgG)- and IgM-specific antibodies were investigated in 68 asymptomatic blood donors (BDs) previously tested as positive between October, 2008, and September, 2009, and living in northeastern Italy. Our study showed that WNV-specific IgG titers became negative (41%) or decreased (33%) in a large percentage of BDs, while they increased in a smaller percentage (10%); 16% of BDs showed no titer variation. Reversion to seronegative status within a short time frame suggests that WNV surveillance should be maintained year after year.

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