<P> After entering the host cell, the viral genome is replicated in the rough endoplasmic reticulum (ER) and in the so - called vesicle packets . At first, an immature form of the virus particle is produced inside the ER, whose M - protein is not yet cleaved to its mature form, so is denoted as precursor M (prM) and forms a complex with protein E. The immature particles are processed in the Golgi apparatus by the host protein furin, which cleaves prM to M . This releases E from the complex which can now take its place in the mature, infectious virion . </P> <P> Yellow fever virus is mainly transmitted through the bite of the yellow fever mosquito Aedes aegypti, but other mostly Aedes mosquitoes such as the tiger mosquito (Aedes albopictus) can also serve as a vector for this virus . Like other arboviruses which are transmitted by mosquitoes, the yellow fever virus is taken up by a female mosquito when it ingests the blood of an infected human or another primate . Viruses reach the stomach of the mosquito, and if the virus concentration is high enough, the virions can infect epithelial cells and replicate there . From there, they reach the haemocoel (the blood system of mosquitoes) and from there the salivary glands . When the mosquito next sucks blood, it injects its saliva into the wound, and the virus reaches the bloodstream of the bitten person . Transovarial and transstadial transmission of the yellow fever virus within A. aegypti, that is, the transmission from a female mosquito to her eggs and then larvae, are indicated . This infection of vectors without a previous blood meal seems to play a role in single, sudden breakouts of the disease . </P> <P> Three epidemiologically different infectious cycles occur, in which the virus is transmitted from mosquitoes to humans or other primates . In the "urban cycle", only the yellow fever mosquito A. aegypti is involved . It is well adapted to urban areas and can also transmit other diseases, including Zika fever, dengue fever, and chikungunya . The urban cycle is responsible for the major outbreaks of yellow fever that occur in Africa . Except in an outbreak in 1999 in Bolivia, this urban cycle no longer exists in South America . </P> <P> Besides the urban cycle, both in Africa and South America, a sylvatic cycle (forest or jungle cycle) is present, where Aedes africanus (in Africa) or mosquitoes of the genus Haemagogus and Sabethes (in South America) serve as vectors . In the jungle, the mosquitoes infect mainly nonhuman primates; the disease is mostly asymptomatic in African primates . In South America, the sylvatic cycle is currently the only way humans can become infected, which explains the low incidence of yellow fever cases on the continent . People who become infected in the jungle can carry the virus to urban areas, where A. aegypti acts as a vector . Because of this sylvatic cycle, yellow fever cannot be eradicated . </P>

When was the cure for yellow fever discovered