Mosquito vectors of West Nile Fever in Israel.

West Nile fever (WNF) is endemic in Israel. In 1999, country-wide adult mosquito surveys were initiated and intensified after the 2000 country-wide outbreak of WNF in humans. In 8 consecutive yr, groups of male and female specimens of different species and from different locations were tested for infection with West Nile virus (WNV). Three species made up >87% of the total catch: Culex pipiens L. (52%), with an infection rate (IR) of 0.5; Cx. perexiguus Theobald (20%), with an IR of 2.7; and Aedes caspius Pallas (15%), with an IR of 0.6. The geographical and temporal distribution of WNV-infected mosquitoes was similar but was not parallel to the seasonal abundance of the populations. The seasonal occurrence of human cases is in correlation with the finding of WNV-positive mosquito specimens reaching a peak 1 mo later than the mosquito peak. The relative importance of the mosquito species in the epidemiology of WNF is discussed. Cx. perexiguus is considered the major vector of WNF in Israel.