The Vector

West Nile virus is transmitted by mosquitoes, and mainly by the Culex spp. which are distributed widely across Europe.

• Mosquitoes
  The incidence of West Nile virus disease is seasonal, primarily occurring from July through October, in line with typical peak activity of mosquitoes, with mosquitoes infected late summer.
  
  Mosquitoes are nectar feeders. However, the female mosquito also requires blood meals for egg production, and has highly modified mouth parts for the purpose of blood-feeding.
  
  The female mosquito becomes infected with West Nile virus by feeding on infected birds. It is within birds that the virus multiplies. The virus is then transmitted by the infected mosquito to other birds, people or animals when the mosquito feeds again.
  
  Mosquitoes tend to be most active between dusk and dawn, preferring still, warm conditions. Due to their size they are not strong fliers and cannot fly in breezy conditions. However they can fly continuously for 1 to 4 hours at 1-2km/h travelling anything up to 10km.
• Habitat
  Mosquitoes need water to reproduce, and so live around moist areas. Any place where water is held for one week or more can serve as a breeding ground for mosquitoes. This can range from wetlands and marshes to storm water filled ditches, rain barrels or any form of artificial container such as discarded tyres.
  
  Some stages of the mosquito are able to overwinter in protected areas, with West Nile virus able to persist in overwintering mosquitoes.