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Yellow fever


THE yellow fever is an infectious disease caused by a flavivirus (the yellow fever virus), for which a highly effective vaccine is available.

The disease is transmitted by mosquitoes and occurs exclusively in Central America, South America and Africa. In Brazil, the yellow fever is usually acquired when an unvaccinated person enters areas of transmission wild (cerrado regions, forests). A person does not transmit yellow fever directly to another.

For this to occur, it is necessary for the mosquito to bite an infected person and, after the virus has multiplied, to bite an individual who has not yet had the disease and has not been vaccinated.

The transmission of yellow fever in wilderness area is made through mosquitoes of the genus (mainly) Haemagogus.

The virus cycle in wild areas It is maintained through the infection of monkeys and the transovarian transmission (mosquito passages to their offspring, children) in the mosquito itself. Human infection occurs when a person unimmunized enters cerrado or forested areas. Once infected, the person may, upon return, serve as a source of infection for the Aedes aegypti, which can then start transmitting the yellow fever in urban area. A person may be a source of mosquito infection from immediately before symptoms appear until the fifth day of infection.

O Aedes aegypti becomes able to transmit the virus of yellow fever 9-12 days after biting an infected person. In Brazil, the transmission of yellow fever in urban areas has not occurred since 1942. In areas of agricultural development frontiers, the wild transmitter may adapt to the new habitat and the consequent possibility of transmission of the yellow fever in rural areas ("intermediate").