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Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

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Different mosquito species (Aedes and Haemogogus) carries thearbovirus of the flavivirus genus from on host to another (primarily between monkeys, from monkeys to humans and from person to person) (1).

  • Aedes spp. mosquitoes are active during daylight hours, and bite from dawn to dusk. Haemagogous spp. mosquitoes that breed in the forest canopy in South America are also daytime biters
  • once infected with the virus, the mosquito remains infectious for life (two to three months).
  • although the mosquito is killed by extremes of heat and cold, the virus can survive from season to season in mosquito eggs, making disease eradication difficult

Incubation period is generally three to six days but may be longer

There are three main transmission cycles.

  • sylvatic (or jungle) yellow fever
    • seen in South America and Africa (2)
    • monkeys infected by wild mosquitoes pass the virus to other mosquitoes that feed on them
    • humans entering the forest (e.g. for logging) are at risk of infected mosquitoes bites
  • intermediate yellow fever
    • occurs in the moist savannah zones of Africa only
    • semi-domestic mosquitoes infect both animals and humans and may cause small epidemics in rural villages (2)
    • most common type of outbreak in Africa
    • can become a more severe epidemic if the infection is carried into an area populated with both domestic mosquitoes and unvaccinated people (1)
  • urban yellow fever
    • occur where the virus is introduced into urban areas and the domestic Aedes aegypti mosquito is present
    • can lead to large epidemics if the virus is introduced into unvaccinated populations

There is no risk of transmission in the UK from imported cases since the mosquito vector does not occur in the UK (3).



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