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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No chicken, organic or conventionally raised, is completely free of pathogens. Seth Perlman/AP hide caption

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Are you a pool-cleaning do-it-yourselfer or do you leave it to the pros? Terence D. Healy/ hide caption

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An Afghan health worker administers the polio vaccine to a child during a vaccination campaign in Kabul, Afghanistan, in 2010. Majid Saeedi/Getty Images hide caption

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A study of Ugandans found antiretroviral drugs can extend the lifespans of people with HIV to nearly normal lengths. Adek Berry/AFP/Getty Images hide caption

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