An RNA virus, Yellow fever belongs to the family flavivirus. Closely related to West Nile and St. Louis encephalitis, yellow fever is primarily transferred by the bite of an infected mosquito. The mosquitoes become infected through consuming blood of infected humans or other primates. Many people do not present any symptoms at all. If they do, fever, chills, body aches, nausea, fatigue, and vomiting can all occur. Fatality is roughly 50%. There is no cure or medication to treat it.

https://www.cdc.gov/yellowfever/transmission/index.html