China’s Père David’s deer was nearly gone in the late 1800s. Just 18 deer — the very last of their kind — were brought into captivity after the rest had been hunted to extinction. When 11 of the deer reproduced, the species had a chance. Today, after centuries of reintroductions and breeding under human care, the population sits at around 3,000. It’s a success story. But that success could come crashing down if chronic wasting disease (CWD) were to infect the population.