CONAKRY, Guinea (AP) — Despite stringent infection-control measures, the risk of Ebola's spread cannot be entirely eliminated, Doctors Without Borders said Friday after one of its doctors caught the dreaded disease while working in Guinea and went to New York City. In another example of how the disease has jumped borders despite increased health checks at land crossings and airports and seaports, Mali reported its first confirmed case of Ebola late Thursday. Mali, which borders both Senegal and Guinea, was long considered highly vulnerable to Ebola's spread. Because symptoms of the disease can take up to 21 days to appear, people can travel long distances before they know they are infected, bringing the disease to a new place.