In South America, infections occur sporadically, and usually among forestry and agricultural workers. In Africa, infections occur primarily in the tropical areas of western and central, but also in urban locations as well as jungle regions. Many countries require that visitors have the yellow fever vaccination prior to entering the country. Yellow fever can affect both sexes, all ages and races. A certain type of mosquito, Aedes aegypti, is most often responsible for transmitting the virus.
Symptoms usually occur within three to six days after exposure.
Initial symptoms may be flu-like and include fever, headache, vomiting, and backache. As the disease progresses, the pulse may slow and weakens, and bleeding of the gums and bloody urine occur. Jaundice may also occur. There is a vaccine available for yellow fever. Because transmission of yellow fever no longer occurs within the United States, it is important for travelers to talk with their physicians about the need to be immunized prior to visiting areas where yellow fever still exists.