Rod-shaped specimens of Yersinia pestis, the bacterial cause of plague, find a happy home here in the foregut of a flea. Fleas can transmit the infection to animals and people, who can get pneumonic plague and transmit the infection through a cough or kiss. Science Source hide caption

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A man stands near collapsed houses in Bhaktapur, on the outskirts of Kathmandu, on April 27, two days after a magnitude-7.8 earthquake hit Nepal. Aftershocks tend to get less frequent with time, scientists say, but not necessarily gentler. Prakash Mathema/AFP/Getty Images hide caption

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Sequencing the genes of a cancer cell turns up lots of genetic mutations — but some of them are harmless. The goal is to figure out which mutations are the troublemakers. Kevin Curtis/Science Source hide caption

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The blood cancer in soft-shell clams poses no risk to humans, but it does kill the shellfish. Pat Wellenbach/AP hide caption

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For someone 2.5 inches shorter than average, the risk of coronary artery disease increases by about 13.5 percent, scientists found. PW Illustration/Ikon Images/Corbis hide caption

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There's a widely held assumption that a slight imbalance in male births has its start at the very moment of conception. But researchers say factors later in pregnancy are more likely to explain the phenomenon. CNRI/Science Source hide caption

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Glenn Lightner in 2012 at age 13. His father searched for years, to no avail, hoping to find a promising experimental cancer treatment that might save his son's life. Courtesy of Lawrence Lightner hide caption

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It's a good start when experimental compounds stop the proliferation of cancer cells in the lab. But, as many researchers have learned the hard way, that's just an early step toward creating a worthwhile treatment. Science Source hide caption

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Tobacco smokers are more likely than nonsmokers to die from infection, kidney disease and, maybe, breast cancer. iStockphoto hide caption

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Dr. Margaret Hamburg will have served almost six years as FDA commissioner by the time she leaves, far longer than the recent tenure for chiefs of the agency. J. David Ake/AP hide caption

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A nurse administers an experimental Ebola vaccine Monday at Redemption Hospital in Monrovia, Liberia. Researchers aim to give shots to 27,000 people during the large trial. John Moore/Getty Images hide caption

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Harvard University student Elana Simon introduces President Obama before he spoke at the White House Friday about an initiative to encourage research into more precise medicine. Mandel Ngan/AFP/Getty Images hide caption

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