TOKYO -- Researchers are starting to get a better read on the Ebola virus, the deadly hemorrhagic fever that continues to plague West Africa.
The good news: The prevailing view is that the infectiousness of the virus, or the ease with which it spreads, has not increased and is unlikely to do so. That means the epidemic should be containable with the proper measures.
Ebola is a single-stranded RNA virus that is approximately 1 micrometer long. When a person is infected, through blood or other bodily fluids, the virus sends ribonucleic acid into cells. In this sense, Ebola is similar to influenza. Ebola does mutate after repeated infections, but experts believe its basic nature remains unchanged.
Five strains of the Ebola virus are known today. The Zaire strain is behind the current outbreak.
A few factors raised concerns about the possibility of mutation leading to increased infectiousness. The Zaire strain usually affects Central Africa, the outbreaks tend to be on a smaller scale, and the mortality rate is usually up to 90% -- higher than in the current epidemic.
"The Zaire Ebola virus [causing the recent epidemic] in West Africa may be different from the one seen in Central Africa," said Dr. Masayuki Saijo, director of the Department of Virology I at the National Institute of Infectious Diseases of Japan.
But scientists believe the main reason for the much broader outbreak is that the virus hit heavily populated areas. At present, there is no evidence that a mutation has made Ebola easier to catch.
Some doctors do worry about the potential for transmitting Ebola through droplets, like the flu. But Narumi Hori, a nurse at Japan's National Center for Global Health and Medicine, is not convinced. If that were the case, she said, there would be a lot more patients.
No time to lose
But what explains the difference in mortality rate? In the ongoing outbreak, roughly half of Ebola patients recover.
Researchers from Tulane University of the U.S. and other institutions analyzed 106 Ebola patients in Sierra Leone, where the epidemic continues. They found that the death rate varies, depending on how much the virus has replicated by the time a patient comes in for treatment.
The mortality rate of Ebola patients with fewer than 100,000 copies of the virus per milliliter of blood was 30%, while the rate exceeded 70% for those with more than 100,000 copies per milliliter.
Dr. John Schieffelin of Tulane University said that many patients could have been saved had they received treatment soon after developing symptoms.
In the study, the falality rate was also higher in older individuals. The figure came in at a little under 60% for patients aged 20 or younger but it surpassed 90% for patients aged 46 and up. Schieffelin said diabetes and high blood pressure, often seen in seniors, may have something to do with the gap.
The World Health Organization on Oct. 29 announced that new Ebola infections appear to be declining, but the work is far from over. Schieffelin stressed that to end the epidemic, new patients still need to be quickly found, isolated and treated appropriately.