Two women check their cellphones as they hawk their wares on a bridge over the Artibonite River, whose waters are believed to be the source of Haiti's 2010 cholera outbreak. Nicholas Kamm/AFP/Getty Images hide caption

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Researchers hope to keep the mosquito that transmits dengue, Aedes aegypti, from infecting humans using the Wolbachia bacterium. James Gathany/CDC Public Health Image Library hide caption

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Pakistani NGO workers protest at a rally on World AIDS Day in Peshawar in 2006. Tariq Mahmood/AFP/Getty Images hide caption

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Women hold mosquito nets after receiving them at a distribution point in Sesheke, Zambia. Researchers say malaria may have rebounded in some parts of Zambia and Senegal because of resistance to the insecticide-treated nets. ASSOCIATED PRESS hide caption

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A vendor sells betel leaf wrapped in silver foil in Lucknow, India. AJAY KUMAR SINGH/ASSOCIATED PRESS hide caption

itoggle caption AJAY KUMAR SINGH/ASSOCIATED PRESS

Although various types of contraceptive methods are available in Nigeria, about 20 percent of women say they're not able to access them. Sometimes their husbands stand in the way. GEORGE OSODI/ASSOCIATED PRESS hide caption

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