The most striking thing about the present outbreak, says Andrew Townsend Peterson, an evolutionary biologist at the University of Kansas who is interested in modelling the spread of Ebola, is that it seems to involve the Zaire strain of the disease, the deadliest of the five subtypes of Ebola known to medicine. But Zaire—the name for the country now known as the Democratic Republic of the Congo—is a long way from Guinea, where the first cases seem to have arisen in December 2013. How did the virus cross that distance One possibility, according to a paper published on July 31st in PLOS Neglected Tropical Diseases, by Dr Daniel Bausch and Lara Scwarz, of McGill University, is that it didn't.