Mary Mallon, known as "Typhoid Mary," was immune to the typhoid she carried. Working as a cook, she spread the disease in New York and ended up quarantined on Brother Island (above) for more than two decades. Bettmann/Corbis hide caption

itoggle caption Bettmann/Corbis

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

itoggle caption Simon Maina/AFP/Getty Images