Clostridium difficile, a bacterium that causes severe diarrhea, can be difficult to treat with antibiotics. Stefan Hyman/University of Leicester hide caption

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Stefan Hyman/University of Leicester

Pandoraviruses were discovered lurking in the mud of Chile and Australia, half a world apart. courtesy of Chantal Abergel and Jean-Michel Claverie hide caption

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courtesy of Chantal Abergel and Jean-Michel Claverie

World's Biggest Virus May Have Ancient Roots

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When flu viruses (in red) accumulate an escape protein too quickly, they exit the cell nucleus (in blue) before they've made enough viral copies to spread the infection. Benjamin tenOever hide caption

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Benjamin tenOever

Bats harbor many types of coronaviruses and were probably the original source of the new coronavirus that appeared in the Middle East. iStockphoto.com hide caption

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iStockphoto.com

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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iStockphoto.com

Health Department officials cull birds and put them in sacks after bird flu virus was detected in Bhubaneswar, India. Biswaranjan Rout/AP hide caption

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Biswaranjan Rout/AP

Bird Flu Studies Getting Another Round Of Scrutiny By Panel

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