As Jimmy Carter turns 100, the world is close to achieving one of his life missions: Eradicating Guinea worm disease

Jimmy Carter became the first U.S. president to live to 100 on Tuesday, a milestone that seemed unlikely more than 18 months ago when his family said he would be entering hospice care in his hometown in Georgia. And while birthday celebrations are under way, a crucial piece of his legacy is being cemented: the world is closing in on eradicating Guinea worm disease, with just four cases so far this year.Mr. Carter and his late wife Rosalynn began leading the global fight to get to zero in the mid-1980s, in hopes of making Guinea worm the second human disease to be eliminated, after smallpox. It was an ambitious goal, but one with significantly more challenges.