The disease is caused by the yellow fever virus and is spread by the bite of the female mosquito. It infects only humans, other primates, and several species of mosquitoes. In cities, it is spread primarily by mosquitoes of the Aedes aegypti species.ellow fever is caused by the yellow fever virus, a 40- to 50- nm-wide enveloped RNA virus, the type species and namesake of the family Flaviviridae. It was the first illness shown to be transmissible by filtered human serum and transmitted by mosquitoes, by Walter Reed around 1900.