question: How is yellow fever virus transmitted?
answer: Yellow fever virus is transmitted by mosquitoes and is restricted to Africa, Central and South America and the Caribbean. 
  Yellow fever virus is a flavivirus, and there is only one antigenic type. It was taken to the Americas by the early slave traders, and nowadays reported in Africa, America, Asia and Europe. Yellow fever virus is transmitted by two different cycles: 
  -from human to human by the mosquito Aedes aegypti; which is well-adapted to breeding around human habitations; the infection can be maintained in this way as ‘urban’ yellow fever.
  -from infected monkeys to humans by mosquitoes such as Haemagogus. This is ‘jungle’ yellow fever and is seen in Africa and South America.
  
  Yellow fever is not transmitted directly from human to human by day-to-day contact, but transmission from ill patients to healthcare workers has been reported, notably after needlestick injury.