U.S. health officials are warning travelers to stay away from certain areas of Brazil if they haven’t been vaccinated against yellow fever. Ten recent tourists, none from the U.S., got the mosquito-borne disease, and four died. The Centers for Disease Control and Prevention, which has long urged travelers to Brazil to get yellow fever shots, issued a report Friday amid a surge of illnesses near major cities. Yellow fever was wiped out in the U.S. over a century ago, and the shot is not part of routine vaccinations. The virus can be spread by the same mosquito that transmits other tropical diseases, including Zika and dengue. Most people recover after fever, chills and other symptoms, but some get more seriously ill and can develop internal bleeding and organ failure.