A doctor examines chest X-rays at a tuberculosis clinic in Gugulethu, Cape Town, South Africa in late 2007. The number of TB cases that don't respond to both first- and second-line medications is rising worldwide. Karin Schermbrucker /AP hide caption

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Two men from northwestern Missouri became ill after tick bites infected them with a previously unknown virus. iStockphoto.com hide caption

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A Beechcraft airplane sprays insecticide over Dallas early Monday morning to curb the spread of West Nile virus. LM Otero/AP hide caption

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People wait in line at the Durham County Health Department for the H1N1 flu vaccination in Durham, N.C., in November 2009. Gerry Broome/AP hide caption

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Families wait for hours to register at the Yida refugee camp in South Sudan along the northern border in early July. Within a few weeks, the population of the camp more than doubled, leading to shortages of food, water and medicine. Paula Bronstein/Getty Images hide caption

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Bill Gates, co-founder of the the Bill & Melinda Gates Foundation, checks out a toilet demo at the Reinvent the Toilet Fair in Seattle, Wash. The festival featured prototypes of high-tech toilets developed by researchers around the world. Bill & Melinda Gates Foundation hide caption

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A newly discovered disease in boa constrictors could provide the missing link in the latent Ebola virus. iStockphoto.com hide caption

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Health officials say they're worried that one day there will be no more antibiotics left to treat gonorrhea. iStockphoto.com hide caption

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Pharmacist Kristy Hennessee administers a vaccination against whooping cough in Pasadena, Calif., in 2010. Vaccinations are the most powerful weapon for slowing the epidemic, but there are growing concerns that the current vaccine doesn't last as long as expected. Robyn Beck/AFP/Getty Images hide caption

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