AntibodiesAgainst Mosquito-born Viruses in Human Population of an Area of Central BohemiaAffected by the Flood of 2002

Overview

In the Central-Bohemian area affected by the flood of 2002, 497 residents were screened forantibodies against the mosquito-borne viruses Ťahyňa (TAHV),West Nile (WNV), Sindbis (SINV) andBatai (BATV; syn. Čalovo) using the haemagglutination-inhibition (HIT) and plaque-reductionneutralization (PRNT) tests. Blood samples were collected in September 2002 when the mosquitopopulations showed the maximum density following the flood. Antibodies against TAHV (16.5 %persons in PRNT, 14.9 % in HIT), SINV (1.4 % in HIT) and BATV (1.4 % in HIT, 0.2 % in PRNT) weredetected. Although 6.8 % and 1.2 % of the subjects tested reactive with WNV in HIT and PRNT,respectively, the results were interpreted as cross-reactivity with tick-borne encephalitis virus. Theseroprevalence of TAHV(both inPRNTand HIT) showed no association with gender (15.8%of males,16.9 % of females), increased with age (1.4 % of persons younger than 20 years, 11.2 % of persons agedbetween 20 and 50 years, and 26.2 % of persons older than 50 years were positive), and correlatedwith the mosquito peri-residential challenge (5.0% residents seropositive in a mosquito-free control zone D – mostly Prague, 14.7 % in a mild-risk zone C, 20.5 % in a moderate-risk zone B, and 28.0 % inthe most heavily mosquito-infested risk zone A). The highest TAHV seropositivity rate (> 25 %) wasfound amongst the inhabitants of the villages Obříství, Kozly, Tuhaň, Chrást, Chlumín and Hostín.Paired blood samples were obtained from 150 of the persons at a 6-month interval: an infectionepisode with TAHV during or after the flood was clearly evidenced in one person living in Obříství,and less convincing findings of recent TAHV infections were found in other three residents ofChlumín and Obříství (seroconversion and/or significant antibody titres increase detected in HITonly). This serosurvey indicated the existence of an active natural focus of Valtice fever (TAHVinfection) stretched along the river Labe nearby Neratovice (Obříství,Chlumín,Tuhaň; Kozly, Tišice,Chrást), and a low TAHV activity area along the lower reaches of the river Vltava between Zlončiceand Bukol/Zálezlice.Anincreased population density of mosquitoes after the floodmayhave boostedthe incidence of mosquito-borne virus diseases, particularly Valtice fever, in Central Bohemia. Anoptimum prophylactic strategy to control these diseases would be epidemiological surveillance(including monitoring of both the density of mosquitoes and their rate of infection with viruses innatural foci) on the basis of which antiepidemic measures such as integrated mosquito control canbe taken.

Key words:
mosquitoes – Culicidae – Ťahyňa virus – West Nile virus – Sindbis virus – Batai virus –Čalovo virus – flood.