Researchers say a man in Africa who recovered from Ebola suffered a relapse nearly six months later that led to 91 new cases before he died. The report adds to evidence that the deadly virus can lurk in the body long after symptoms end, and that survivors need monitoring for their own welfare and to prevent spread. Relapses like this one from an outbreak in the Democratic Republic of Congo are thought to be rare. This is the first one clearly shown to have spawned a large cluster of new cases. The New England Journal of Medicine published details on Wednesday.