Monkeypox, a virus transmitted to humans mostly through small rodents (and less commonly monkeys) was first identified in 1970, and infections have typically been confined to the parts of western and central Africa where it is endemic. The disease is usually mild, with symptoms including fever and rashes clearing within a few weeks. This makes the latest outbreak, four-fifths of which is occurring in Europe, surprising and unusual. Since May, cases have climbed significantly, tripling in