Absence of indigenous specific West Nile virus antibodies in Tyrolean blood donors

In the last several years, West Nile virus (WNV) was proven to be present especially in the neighboring countries of Austria, such as Italy, Hungary, and the Czech Republic, as well as in eastern parts of Austria, where it was detected in migratory and domestic birds. In summer 2010, infections with WNV were reported from Romania and northern Greece with about 150 diseased and increasingly fatal cases. We tested the sera of 1,607 blood donors from North Tyrol (Austria) and South Tyrol (Italy) for antibodies against WNV by using IgG enzyme-linked immunosorbent assay (ELISA). Initial results of the ELISA tests showed seroprevalence rates of 46.2% in North Tyrol and 0.5% in South Tyrol, which turned out to be false-positive cross-reactions with antibodies against tick-borne encephalitis virus (TBEV) by adjacent neutralization assays. These results indicate that seropositivity against WNV requires confirmation by neutralization assays, as cross-reactivity with TBEV is frequent and because, currently, WNV is not endemic in the study area.