Boys show off their four-legged friends at a rabies vaccination drive set up by the Serengeti Health Initiative in the Bariadi District of Tanzania. Anna Czupryna/Courtesy of Serengeti Health Initiative hide caption

itoggle caption Anna Czupryna/Courtesy of Serengeti Health Initiative

Do you know what the deadliest disease is? Hint: It's not Ebola (viral particles seen here in a digitally colorized microscopic image, at top right, along with similar depictions of other contagious diseases) NPR Composite/CDC hide caption

itoggle caption NPR Composite/CDC

Vampire bats are common in Central and South America, where they feed on livestock and sometimes people. Michael & Patricia Fogden/Corbis hide caption

itoggle caption Michael & Patricia Fogden/Corbis