A man readies a cow for the International Highland Cattle Show in Glasgow, Scotland. Researchers say genetics and the amount of time animals and humans spend together can affect how viruses spread between species.
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Laurence Fishburne as Dr. Ellis Cheever and Kate Winslet as Dr. Erin Mears in the thriller Contagion. Winslet's character was modeled on CDC epidemiologist Dr. Anne Schuchat.
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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.
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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.