The cruise ship Carnival Magic floats behind a catamaran off Cozumel, Mexico on Oct. 17. The ship skipped a planned stop there Friday, the cruise line says, after Mexican authorities delayed granting permission to dock. Reuters/Landov hide caption

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Avian influenza, or bird flu, causes an infectious and contagious respiratory disease. In the lab, several scientists have made the H5N1 strain more contagious, a controversial line of research. James Cavallini/ScienceSource hide caption

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A stencil of an early human's hand in an Indonesian cave is estimated to be about 39,000 years old. Kinza Riza/Courtesy of Nature.com hide caption

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Traffic moves past Texas Health Presbyterian Hospital in Dallas, where a patient showed up with symptoms that were later confirmed to be Ebola. Mike Stone/Getty Images hide caption

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Biohazard suits used to handle dangerous microbes hang in a laboratory at the U.S. Army Medical Research Institute of Infectious Diseases in Fort Detrick, Md. Patrick Semansky/AP hide caption

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Medical workers at the John F. Kennedy Medical Center in Monrovia, Liberia, put on their protective suits before going to the high-risk area of the hospital, where Ebola patients are being treated, Sept. 3. Dominique Faget/AFP/Getty Images hide caption

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Proteins and enzymes that will produce antibodies for the experimental Ebola drug ZMapp are developed on the leaves of the nicotiana benthamiana plant, a relative of tobacco. Here, indicator proteins glow under ultraviolet light — a way to assess the success of bacteria spread. Sean Gallup/Getty Images hide caption

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Workers with the aid group Doctors Without Borders prepare a new Ebola treatment center near Monrovia, Liberia, on Sunday. The facility has 120 beds, making it the largest Ebola isolation clinic in history. John Moore/Getty Images hide caption

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Kenyan health officials take the temperatures of passengers arriving at the Nairobi airport on Thursday. Kenya has no reported cases of Ebola, but it's a transportation hub and so is on alert. Simon Maina/AFP/Getty Images hide caption

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An outbreak of bird flu in India in 2008 prompted authorities to temporarily ban the sale of poultry. Diptendu Dutta/AFP/Getty Images hide caption

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