Serologic survey of potential vertebrate hosts for West Nile virus in Poland

A survey for antibodies to West Nile virus (WNV; genus Flavivirus) was carried out by plaque-reduction neutralization microtesting in 78 horses, 20 domestic chickens, and 97 wild birds belonging to 10 species from different areas in Poland. Specific antibodies were detected in five juvenile (hatching-year) birds collected in 2006: three white storks (Ciconia ciconia) in a wildlife rehabilitation center (5.4% of all examined storks; the antibody titers in each bird were 1: 320, 1: 160, and 1: 20), one free-living mute swan (Cygnus olor; the titer was 1: 20), and one hooded crow (Corvus corone cornix; the titer 1: 20) in a wildlife rehabilitation center; thus the overall seropositivity to WNV was 5.2% among all the birds sampled. These data do not rule out the presence of WNV activity in Poland with 100% certainty, but they indicate a significant trace that demands verification. In addition, one black-headed gull (Larus ridibundus) had neutralizing antibodies for the Usutu Flavivirus, the first case recorded in Poland.