In Europe and surrounding countries as of 4 October 2012, the highest recorded activity is currently in the Russian Federation. Other countries with large numbers of cases are Greece, Israel, Serbia and Italy. Over the years, however, the infection has been reported from many other areas particularly northern and eastern African states.
In the USA according to the latest report from the Centers for Disease Control and Prevention as of 2 October there have been 3,969 cases this year including 163 deaths. This is the highest number of cases and deaths reported in USA since 2003.
Almost 70 per cent of the cases have been reported from eight states (Texas, California, Louisiana, Mississippi, South Dakota, Michigan, Oklahoma, and Illinois.)
Texas has so far accounted for a third of all cases reported.
Human infections vary in severity with most infections being asymptomatic or resembling a mild influenza-like illness but especially in the elderly or in those who have other medical problems which might reduce resistance the infection can develop into a neurological illness including meningitis and/or encephalitis. The virus is transmitted by Culicine mosquitoes. There is no available vaccine and prevention depends on measures to avoid mosquito bites.