Thanks to John Ballard for tweeting the link to this September 5 New York Times article: Many in West Africa May Be Immune to Ebola Virus. Excerpt:
Although few medical experts realize it, part of the population in West Africa is immune to the Ebola virus, according to virologists who specialize in the disease.
Assuming they are correct, and if those people can be identified, they could be a great help in fighting the outbreak. Immune persons could safely tend the sick and bury the dead just as smallpox survivors did in the centuries before smallpox vaccine.
Also, antibodies could be harvested from their blood to treat new Ebola victims.
But many factors remain unclear, including which Africans have antibodies and how much antibody is needed to be protective. The biggest mystery is how the immunity arose, and there is a mix of explanations, like silent infections and fruit contaminated with bat saliva.
“It’s fair to say that some people are immune,” said Robert F. Garry Jr., a Tulane University expert in hemorrhagic fevers who works in Sierra Leone. “But we don’t know if it’s 1 percent or 2 percent or 20 percent.”
Right now, there are about 1,800 survivors of the current West African outbreak, all of whom are now immune, of course. But there may be many thousands more.
Small studies of household contacts of Ebola victims show that some people are infected without ever falling ill — perhaps because of some unknown genetic advantage.
But many Africans who have never seen a victim also have antibodies.
It is possible that some get low doses of virus by eating infected monkeys or bats that are undercooked.
“If someone got just two or three or four virus particles, if it enters through the mucus membranes in the mouth, yes, it’s plausible,” said Thomas W. Geisbert, a hemorrhagic fever expert at the University of Texas Medical Branch in Galveston. “It would take a while for the virus to get going, and it’s a race with the clock. The immune system gets a chance to fight it off.”
Antibodies, Y-shaped proteins that attach to a virus and block it from invading cells, are the immune system’s first line of defense; the second line is white blood cells primed to recognize and digest the virus.
One of France’s leading Ebola experts says he believes that many rural villagers are “vaccinated” by eating fruit gnawed on by bats and contaminated with their saliva.
“We imagine that this is the main route,” said Dr. Eric M. Leroy, a veterinarian and virologist at the International Center for Medical Research in Franceville, Gabon. “But it is a hypothesis. We do not have the evidence.”