In an interview with the New York Times, Tom Inglesby, director of the Johns Hopkins Centre for Health Security, said that although it's too soon to say for sure, the symptoms are "consistent with poisoning." So far, we know people have died from heart attacks, as well as internal bleeding and fluid in the lungs and brain. "It’s rare for travellers to die of unknown causes like this, and to have a high number of them in a relatively short period of time is alarming, shocking, sad," he told the Times. "It’s something that investigators should be able to get to the bottom of."