Even as government officials express confidence that researchers know the key facts about Ebola, many questions crucial to preventing an outbreak in the United States remain unanswered, scientists told a workshop at the National Academy's Institute of Medicine in Washington on Monday.
Virtually all the unknowns have practical consequences, participants emphasized, making it foolish and perhaps dangerous to base policy on weak science.
For instance, virologists believe that Ebola is spread when people come in contact with the virus-laden bodily fluids of those who are already sick and then touch their eyes, nose or mouth, allowing the virus to pass through mucous membranes and enter the bloodstream.
But penetration through intact skin has not been definitively ruled out, said hemorrhagic-fever expert Thomas Ksiarek of the University of Texas Medical Branch (UTMB), who co-led a session on Ebola's transmission routes.
"Does bleach or hand sanitizer," which people in West Africa are using to protect themselves from Ebola, "make the skin more susceptible" to being penetrated by the virus?, Peters wondered. "It's a question that has to be asked."
Another crucial question is whether the virus can be spread by people who do not show symptoms. For months public health officials in the United States and elsewhere have insisted it cannot.
But the possibility of such "subclinical transmission" remains very much open, said Dr. Andrew Pavia, chief of pediatric infectious diseases at the University of Utah.
Nor do experts know whether the infectious dose of virus depends on how it enters the body, Pavia said.
Also unknown is whether the time between exposure to Ebola and the appearance of symptoms depends on which bodily fluids someone contacted. If it does, then someone exposed through, say, saliva rather than blood might incubate the virus for longer than the 21 days officials have repeatedly said is the outer limit of the incubation period.
That was the longest incubation time during the 1976 Ebola outbreak, said Dr. C.J. Peters, a field virologist at UTMB.
But "I would guess that 5 percent of people" can transmit the virus after incubating it for more than three weeks, said Peters, whose battle against the Ebola outbreak in a monkey colony in Virginia was recounted in Richard Preston's 1994 book "The Hot Zone."
Health officials emphasize the importance of taking the temperature of those exposed to Ebola, since people are not thought to be infectious until they run a fever of 100.4 F. (38 C). But at what temperature patients start shedding virus is not definitively known, said Dr. Michael Hodgson, chief medical officer of the Occupational Safety and Health Administration.
Environmental mysteries also remain.
Scientists do not know whether foam, gas, or liquid decontaminants are most effective for cleaning surfaces that might harbor Ebola.
Nor do they know whether it can survive in sewers where, said Paul Lemieux of the National Homeland Security Research Center at the Environmental Protection Agency, rats "might pick it up."
UNICEF announced Monday that it is doubling its staff, from 300 to 600, to fight Ebola in Guinea, Liberia and in Sierra Leone, where children make up 20 percent of all cases of the deadly virus.
Ebola coordinator Dr. Peter Salama of UNICEF said at least 4,000 children have been orphaned by Ebola.
Salama said that schools are closed and children are confined to their homes and discouraged from playing with other kids: “Death is all around them.”
His announcement at the United Nations in New York came as Sierra Leone announced that a fifth local doctor has succumbed to the disease. It is a blow to efforts to keep desperately needed health workers safe in a country ravaged by the deadly virus.
The World Health Organization said Ebola has killed some 5,000 people.
Ebola is high on the agenda of a regional meeting of the WHO that opened Monday in Benin, a West African nation that has not had any Ebola cases.
Asian countries are not contributing enough to the global effort to fight Ebola, despite having a wealth of trained medical personnel who could help stop the spread of the deadly virus, World Bank Group president Jim Yong Kim said on Tuesday.
“Many countries in Asia who could help simply are not, especially when it comes to sending health workers,” Kim told a news conference in Seoul.
South Korea has pledged to contribute $5.6 million dollars to combat the virus, and both Japan and China have sent equipment or medical staff to the Ebola-stricken countries in West Africa.