West African Ebola virus strain less virulent than prototype 1976 strain

Using cynomolgus macaques to model infection and disease in humans, scientists from NIH's National Institute of Allergy and Infectious Diseases (NIAID) infected three animals with 1976 EBOV-Mayinga and three with 2014 EBOV-Makona. While both groups of animals were shedding virus three days after being infected, those in the Mayinga group developed a rash on day four and became extremely ill at days five and six. Those in the Makona group did not develop a rash until six days after infection, and severe disease appeared on days seven and eight. Further, liver damage -- typical in Ebola disease -- was delayed by about two days in the Makona group compared to the Mayinga group.

Of note, the scientists reported that the immune system of animals in the Makona group produced about three times the amount of a virus-fighting protein, interferon gamma, compared to the Mayinga group. They plan more studies of the immune response, but believe that at least seven days are needed after Ebola infection to mount an effective response. This response does not seem to develop during EBOV-Mayinga infection in cynomolgus macaques because disease progression is too fast.