Yellow fever is a serious flu-like disease spread by mosquito bites. It is not curable but can be prevented with a vaccine, using insect repellent, and wearing protective clothing. The illness ranges in severity from fever to liver damage to possible death.
A yellow fever outbreak that began a year and a half ago in Brazil is spreading further, with additional cases since last July in the Brazilian states of Sáo Paulo, Minas Gerais and Rio de Janeiro, plus several cities in Bahia State.
The World Health Organization began recommending yellow fever vaccination for all travelers and residents of these areas in January, but since then, 10 travelers have contracted the disease—all unvaccinated—and four died.