Ebola virus not becoming more dangerous: study

The Ebola virus circulating in West Africa for the past year, deadly as it is, is not showing any evidence of being more dangerous than the first one that emerged in 1976, according to a U.S. study published Tuesday.

Instead, researchers from the U.S. National Institutes of Health (NIH) found that the current strain, called Makona, might have "a decreased ability to cause disease" in an animal model than the original Mayinga strain, which was isolated in Central Africa in 1976.

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.

The results provide important information to scientists, as they wondered if the Ebola virus in West Africa is becoming more severe, the NIH researchers reported in the U.S. journal Emerging Infectious Disease.

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 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. Endite