West Nile virus (WNV) is a small, enveloped, spherical
virus that belongs to the
family Flaviviridae, genus
Flavivirus,
Japanese encephalitis serocomplex. Natural
reservoirs of WNV are
birds, and the main vectors are
mosquitoes of the genus
Culex. There are seven genetic lineages of WNV. Lineages 1 and 2 are the most widely distributed (
Africa, North and
South America,
Europe,
Asia and
Australia). About 80% of
infections are asymptomatic. In 20% of
patients nonspecific febrile
disease occurs (
West Nile fever). Less than 1% of infected
persons will develop neuroinvasive WNV
disease (
meningitis,
encephalitis, and
poliomyelitis). In
Croatia,
antibodies to WNV were demonstrated in
humans,
bears and
horses. In August-September 2012 clinical cases of
human WNV neuroinvasive
disease and asymptomatic acute
infection in
horses were reported for the first
time in three eastern Croatian counties. The
diagnosis was confirmed by
serologic tests (
enzyme immunoassay,
IgG avidity, plaque-reduction
neutralization test).