Quite abruptly, the world has jolted into another infectious-disease crisis. On Friday, Africa CDC confirmed a new Ebola outbreak, centered in the Democratic Republic of the Congo; within two days , the World Health Organization declared the epidemic a public-health emergency of international concern. The virus, which has also spread to Uganda, is suspected to have sickened more than 500 people and killed more than 130—counts that suggest to experts that it has been spreading largely undetected