As if we needed another reason to freak out about Ebola, new research suggests that the speed at which it’s spreading is totally out of proportion to past outbreaks. Thomas House, a mathematician at the UK’s University of Warwick, used historical data from outbreaks reported by the World Health Organization—24 in total—to create a mathematical model for the spread of the virus. By analyzing information on the timing of the outbreaks, the number of cases, and the number of people who died, he was able to develop a model that describes the pattern of all outbreaks—except for one. The current outbreak is off the charts.

“What the results seem to indicate is that it isn’t just an extreme event,” House said when I spoke to him on the phone. It doesn’t fit within the established pattern. “It’s becoming more and more likely that there’s something different this time.”

House isn’t alone in his concern. Other models of Ebola are just as worrying. According to one model reported on by NPR, we should expect to see about 15,000 cases by mid-October. (So far, about 5,000 have been reported.) Researchers led by Jeffrey Shaman, an associate professor at Columbia University’s Mailman School of Public Health, say the virus is spreading at an “exponential” rate. “It's an unprecedented outbreak that requires an enormous response if it is to be controlled,” Shaman said in an email. Alessandro Vespignani, a biological physicist at Northeastern University, told NPR we should be prepared to see as many as 10,000 to 25,000 cases by mid-October. 

House can’t say what exactly it is that’s different about this outbreak. “It could be a mutation,” he said. “It could be that the way that society is structured has changed as West Africa’s developed: People are in contact with more other people. It could be that control efforts or the behavioral response are just different. My model isn’t detailed enough to say exactly which one.” It is detailed enough to raise the panic level, though.