Yellow fever is a viral infection spread by a particular type of mosquito. The infection is most common in areas of Africa and South America, affecting travelers to and residents of those areas.
In mild cases, yellow fever causes fever, headache, nausea and vomiting. But yellow fever can become more serious, causing heart, liver and kidney problems along with bleeding (hemorrhaging). Up to 50 percent of people with the more severe form of yellow fever die of the disease.
There's no specific treatment for yellow fever. But getting a yellow fever vaccine before traveling to an area in which the virus is known to exist can protect you from the disease.