Endemic to Central and West Africa, monkeypox has been making headlines in Europe and the United States. An initially small outbreak of the poxvirus—a relative of the much deadlier smallpox—has been rippling through countries including Spain, Belgium, the United Kingdom, Germany, and Canada. A case in Massachusetts was confirmed by the Centers for Disease Control and Prevention last week and, at the time of this writing, additional cases have been identified elsewhere in the United States.