“The reasons are really unclear,” said Dr. Gilles van Cutsem, who helped run the agency’s response in Liberia and gave a presentation describing its experience at an AIDS conference here.
Doctors Without Borders — better known by its French name, Médecins Sans Frontières — has cared for more Ebola patients in West Africa than any other organization. At its peak, it was running 22 centers; it now runs eight.
Since last March, the average death rate at those remaining centers has dropped to 52 percent, from about 62 percent.
Although patients are getting more intravenous hydration and more nursing care as staff members have more time, the agency does not believe that accounts for the whole difference.
Rather, patients are arriving with less virus in their blood. Viral loads have dropped by almost half, Dr. van Cutsem said, which increases a patient’s chances of survival enormously.
Initially, he said, the assumption was that patients were coming in earlier in the course of their illnesses. Rumors that everyone who entered Ebola centers died were once rife, but now have faded.
But that was not the case, either. According to interviews with patients, the time between the first appearance of symptoms and the day they arrive has not changed.
“That leaves us with two hypotheses,” Dr. van Cutsem said.
One is that fear has made West Africans more careful, and that even those who are infected have gotten smaller amounts of virus into their eyes or mouths. Perhaps they are wearing gloves when they bury bodies, he said, or at least partially protecting themselves while caring for sick relatives.
In many diseases, the size of a viral dose may make the difference between life and death. Even though viruses multiply, immune systems handle small amounts of virus better than large ones.
The other theory is that the virus has mutated to be less lethal. But Dr. van Cutsem said he knew of no genetic evidence to prove that."
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