Yellow fever is a hemorrhagic fever caused by a virus spread by a particular species of mosquito. It 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 bleeding (hemorrhaging), heart, liver and kidney problems. Up to 50 percent of those with the more severe form of yellow fever die of the disease.

There is 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.