The yellow fever virus is not transmitted by direct inter-human contagion, but only through the bite of infected mosquitoes belonging to the genus Aedes (in urban environments), Haemagogus and other sylvan mosquitoes (in the jungle). The species most involved in the transmission of yellow fever, both in Africa and in America, is Aedes aegypti .
People affected by yellow fever - both in apparent form and asymptomatic - have been infected just before the onset of fever for the entire duration of the febrile period (on average 5 days). Feeding on a person with viremia, mosquitoes become infectious about 2 weeks after the blood meal and remain so for the duration of their life.
To prevent the further spread of yellow fever, it is necessary to avoid further mosquito bites in sick people by insulating them in environments protected by mosquito nets, taking into account the "daytime" habits of these insects.
