Investigation on natural infection of the encephalitis B virus of mosquitoes in pig houses in early spring

  Objective   To investigate the natural infection of the epidemic encephalitis B virus of mosquitoes in the pig houses in early spring in the temperate zone.

  Methods   From march 1^st to May 31^st, every day from 18:00 p.m.to 6:00 a.m.of the next morning, mosquitoes were caught with lead-mosquito-lamp in the pig houses in Chenhebang, Fengxian district, Shanghai. The virus was identified with R T-PCT.

  Results   4 428 mosquitoes collected in 2001 and 8 268 in 2002 were identified of the same species, the 8^th species of the 4^th genus. The superior mosquito species caught in 2001 and those of 2002 were all Culex Tritaeniorhynchus, constituting 57.81% and 72.04% respectively. There was remarkable difference in blood absorption between Culex Tritaeniorhynchus and other species of mosquitoes (χ²=17.127, P < 0.01).In Culex Tritaeniorhynchus caught in 2001, the encephalitis B virus was first found on May 22^nd.Of the 99 groups of samples examined, 49.49% were male mosquitoes. In those caught in 2002, the virus was first identified on may 19^th.

  Conclusion   The natural infection of encephaitis B virus of mosquitoes began in late May in the temperate zone.Culex Tritaeniorhynchus was the first infected species in both two years and was more likely to take the virus than other species of mosquitoes, which can provide scientific support for the prediction of the happening time and prevalence intension of the epidemic encephalitis B virus.