A health worker prepares to exit the isolation area at the Ebola clinic run by Doctors without Borders in Lofa County, Liberia. The exponential growth of the outbreak is most aggressive in Liberia.
Tommy Trenchard for NPR
Marina Silva, shown here in Rio de Janeiro on Wednesday, is tied in polls with incumbent President Dilma Rousseff. Silva, the candidate for Brazil's Socialist Party, says if elected next month, she would be "the first social environmentalist president."