Surveillan-ce of Mosquito-borne Viruses in the Břeclav Area (Czech Republic) after the 1997Flood

Summary

In July 1997, devastating floods occurred after heavy rains in Moravia, Czech Republic. Mosquitopopulations increased abruptly in the flooded area thereafter. We carried out a surveillance formosquito-borne virus infections in the Břeclav area, South Moravia, including serosurveys ofinhabitants. A total of 11,334 female mosquitoes in 117 pools (9 100 Aedes vexans, 917 A. cinereus, 11A. cantans, 1 074 A. sticticus and 232 Culex pipiens pipiens) were examined by virological methods.Seven virus isolates were obtained: six of them Ťahyňa virus (Aedes vexans 5, A. cinereus 1), whileone was West Nile (WN) virus (Culex p. pipiens – first isolation in the Czech Republic). Sera of 619local inhabitants were examined in plaque-reduction neutralization test, and antibodies to Ťahyňavirus were detected in 333 (53.8%) and to WN virus in 13 (2.1%). In 72 individuals, paired sera weresampled: a significant increase of antibody titre was detected once against Ťahyňa virus (a subcli-nical infection) and 4 times against WN virus (two children had an illness compatible with WN fever).Of the nine remaining WN seroreactors, three other revealed clinical symptoms compatible withWN fever in summer 1997. The data indicate WN virus activity in the Břeclav area, and describethe first cases of WN fever in Central Europe. The WN virus should not be underestimated asa potential agent of local epidemics even in the temperate climate of Central Europe. Environmentalfactors including human activities which enhance vector population densities (heavy rains followedby floods, irrigation, higher temperature) can produce an increased incidence of mosquito-bornediseases, including WN fever.

Key words:
mosquitoes – Aedes – Culex – Ťahyňa virus – West Nile virus – flood.