West Nile virus investigations in South Moravia, Czechland

Seven virus isolates were obtained from 11,334 mosquitoes after the 1997 Mo rava River flooding in South Moravia (Czech Republic): 6 strains of Tahyna bunyavirus, California antigenic group (5 from Aedes vexans, 1 from Ae. cin ereus), and 1 strain of West Nile flavivirus (WNV) from Culex pipiens. In 1 999, one isolate of Tahyna virus from Ae. vexans and one isolate of WNV fro m Cx. pipiens were recovered from a total of 14,354 mosquitoes examined in the same area, whereas no virus was detected there in 1,179 overwintering m osquitoes (mostly Cx. pipiens) in March 2000. The infection rate of mosquit oes with arboviruses was significantly higher in 1997, the year of the floo d and an enormously high population density of mosquitoes. Antibodies neutr alizing WNV were detected in 13 of 619 (2.1%) hospitalized patients or pers ons seeking outpatient clinics of the area in 1997. Five of the seroreactor s revealed clinical symptoms compatible with West Nile fever: in 2 of them (children), recent infection with WNV was confirmed by a significant increa se of antibody titer between acute and convalescent serum samples.