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Ebola: What don't we know?

U.S. officials leading the fight against history's worst outbreak of Ebola have said they know the ways the virus is spread and how to stop it. They say that unless an air traveler from disease-ravaged West Africa has a fever of at least 101.5 degrees or other symptoms, co-passengers are not at risk.

"At this point there is zero risk of transmission on the flight," Dr. Thomas Frieden, director of the federal Centers for Disease Control and Prevention, said after a Liberian man who flew through airports in Brussels and Washington was diagnosed with the disease last week in Dallas. (The man died Wednesday.)

Other health officials have voiced similar assurances, saying Ebola is spread only through physical contact with a symptomatic individual or their bodily fluids. Yet some scientists who have long studied Ebola say such assurances are premature — and they are concerned about what is not known about the latest strain. It is an Ebola outbreak like none seen before, jumping from the bush to urban areas, giving the virus more opportunities to evolve as it passes through multiple human hosts.

Dr. C.J. Peters, who battled a 1989 outbreak of the virus among research monkeys and who later led the CDC's most far-reaching study of Ebola's transmissibility in humans, said he would not rule out the possibility that it spreads through the air in tight quarters. "We just don't have the data to exclude it," said Peters, who continues to research viral diseases at the University of Texas in Galveston.

Dr. Philip K. Russell, a virologist who oversaw Ebola research while heading the U.S. Army's Medical Research and Development Command, also said much was still to be learned. "Being dogmatic is, I think, ill-advised, because there are too many unknowns here."

If Ebola were to mutate on its path from human to human, said Russell and other scientists, its virulence might wane — or it might spread in ways not observed during past outbreaks, which were stopped after transmission among just two to three people, before the virus had a greater chance to evolve.

"I see the reasons to dampen down public fears," Russell said. "But scientifically, we're in the middle of the first experiment of multiple, serial passages of Ebola virus in man. ... God knows what this virus is going to look like. I don't."

Tom Skinner, a spokesman for the CDC, said health officials were basing their response to Ebola on what has been learned from battling the virus since its discovery in central Africa in 1976. The CDC remains confident, he said, that Ebola is transmitted principally by direct physical contact with an ill person or their bodily fluids.

Skinner also said the CDC is conducting lab analyses to assess whether the new strain of Ebola is mutating in ways that would require changes in how to respond it. The results so far have not provided concern, he said.

The researchers reached in recent days for this article cited grounds to question U.S. officials' assumptions in three categories.

1. Can airport screenings of prospective travelers to the U.S. from West Africa can reliably detect those who might have Ebola?

The CDC says all travelers from West Africa are screened for fever before they get on planes. Individuals who have flown recently from the affected countries suggested that travelers could easily subvert the screening — and might have incentive to do so: Compared with the depleted medical resources in Liberia, Sierra Leone and Guinea, the prospect of hospital care in the U.S. may offer an Ebola-exposed person the only chance to survive. A person could pass body temperature checks performed at the airports by taking ibuprofen or any common analgesic. And prospective passengers have much to fear from identifying themselves as sick.

Sheka Forna, a dual citizen of Sierra Leone and Britain who manages a communications firm in Freetown, said he considered it "very possible" that people with fever would medicate themselves to appear asymptomatic. It would be perilous to admit even nonspecific symptoms at the airport, Forna said in a phone interview. "You'd be confined to wards with people with full-blown disease."

(The federal government announced Wednesday that it will screen most travelers arriving from West Africa at five major airports. The checks will include the taking of temperatures. The screenings will begin Saturday at New York's JFK airport and then expand to Washington Dulles, Atlanta, Chicago and Newark.)

2. Can asymptomatic patients spread Ebola?

The CDC says they cannot. This assumption is crucial for assessing how many people are at risk of getting the disease. Yet diagnosing a symptom can depend on subjective understandings of what constitutes a symptom, and some may not be easily recognizable. Is a person mildly fatigued because of short sleep the night before a flight — or because of the early onset of disease?

Moreover, said some public health specialists, there is no proof that a person infected — but who lacks symptoms — could not spread the virus to others. "It's really unclear," said Michael Osterholm, a public health scientist at the University of Minnesota who recently served on the U.S. government's National Science Advisory Board for Biosecurity. "None of us know."

Russell, who oversaw the Army's research on Ebola, said he found the epidemiological data unconvincing. "The definition of 'symptomatic' is a little difficult to deal with," he said. "It may be generally true that patients aren't excreting very much virus until they become ill, but to say that we know the course of (the virus' entry into the bloodstream) and the course of when a virus appears in the various secretions, I think, is premature."

3. Is the official assertion that Ebola cannot be transmitted through the air correct?

In 1989, virus researcher Charles Bailey supervised the government's response to an outbreak of Ebola among several dozen rhesus monkeys housed for research in Reston, Va. What Bailey learned from the episode informs his suspicion that the current strain of Ebola afflicting humans might be spread through tiny liquid droplets propelled into the air by coughing or sneezing.

"We know for a fact that the virus occurs in sputum and no one has ever done a study (disproving that) coughing or sneezing is a viable means of transmitting," he said. Unqualified assurances that Ebola is not spread through the air, Bailey said, are "misleading."

Skinner of the CDC said that while the evidence "is really overwhelming" that people are most at risk when they touch either those who are sick or such a person's vomit, blood or diarrhea, "we can never say never" about spread through close-range coughing or sneezing.

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