Yellow fever is a serious, potentially deadly flu-like disease spread by mosquitoes. Characterized by a high fever and jaundice, it is most prevalent in certain parts of Africa and South America. The disease is not curable, but is preventable with the yellow fever vaccine.ellow fever is caused by the yellow fever virus (YFV), also called Flavivirus. The virus is transmitted by female mosquitos, who pick it up from monkeys or other humans, then delivers it to a new human when they bite and suck blood. The disease cannot be spread from person to person.