PRINCETON – It may, in the end, turn out to be fortunate that a handful of people in developed countries – four in the United States and one in Spain – have contracted Ebola. Tragic as this was for Thomas Duncan, the only one of these patients who has died, if all of the more than 13,000 cases and nearly 5,000 deaths had occurred in Africa, Ebola would never have aroused nearly as much attention in rich countries.