The Ebola virus that ravaged in West Africa last year is less virulent than the first one that emerged in 1976, says a new study.
Instead, researchers from the US National Institutes of Health (NIH) found that the current strain, called Makona, might have "a decreased ability to cause disease" in an animal model compared to the original Mayinga strain, which was isolated in Central Africa in 1976, according to the study published on Tuesday.
In an animal model called cynomolgus macaques, the current strain, still present in Sierra Leone and Guinea, takes roughly two days longer to cause terminal disease when compared to the 1976 strain, they said.
In the new study, the researchers infected three cynomolgus macaques with the 1976 strain and another three with the current strain.
While both groups were spreading the virus three days after being infected, those with the 1976 strain developed a rash on day four and became extremely ill on days five and six.
Those with the current strain 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 current strain-infected group compared to the group with the 1976 strain.
In humans, the current outbreak, which has killed over 11,000 people, has a case-fatality rate of 50 percent, while the 1976 one has a case-fatality rate of 90 percent.
"It seems fair to conclude that virulence of the strain from West Africa in macaques is not increased compared with other EBOV (Ebola virus) strains," the researchers wrote.