“In Guinea, it is the Zaire strain of Ebola virus. This is the most aggressive and deadly. It kills more than 9 out of 10 patients,” said Michel Van Herp, an MSF epidemiologist currently in Guekedou. “To stop the outbreak, it is important to trace the chain of transmission. All contacts of patients likely to have been contaminated should be monitored and isolated at the first sign of infection.”