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.
Other
public health officials have voiced similar assurances, saying Ebola is
spread only through physical contact with a symptomatic individual or
their bodily fluids. "Ebola is not transmitted by the air. It is not an
airborne infection," said Dr. Edward Goodman of Texas Health
Presbyterian Hospital in Dallas, where the Liberian patient remains in
critical condition.
Yet some scientists who have long studied
Ebola say such assurances are premature — and they are concerned about
what is not known about the strain now on the loose. 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 housed
in Virginia 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, and
who later led the government's massive stockpiling of smallpox vaccine
after the Sept. 11 terrorist attacks, 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. The present outbreak in
West Africa has killed approximately 3,400 people, and there is no
medical cure for Ebola.
"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 in Atlanta, 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 ongoing lab analyses to assess whether
the present strain of Ebola is mutating in ways that would require the
government to change its policies on responding to it. The results so
far have not provided cause for concern, he said.
The researchers
reached in recent days for this article cited grounds to question U.S.
officials' assumptions in three categories.
One
issue is whether airport screenings of prospective travelers to the
U.S. from West Africa can reliably detect those who might have Ebola.
Frieden has said the CDC protocols used at West African airports can be
relied on to prevent more infected passengers from coming to the U.S.
"One
hundred percent of the individuals getting on planes are screened for
fever before they get on the plane," Frieden said Sept. 30. "And if they
have a fever, they are pulled out of the line, assessed for Ebola, and
don't fly unless Ebola is ruled out."
Individuals who have flown
recently from one or more of the affected countries suggested that
travelers could easily subvert the screening procedures — and might have
incentive to do so: Compared with the depleted medical resources in the
West African countries of 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, said Kim Beer, a
resident of Freetown, the capital of Sierra Leone, who is working to get
medical supplies into the country to cope with Ebola.
"It is
highly unlikely that someone would acknowledge having a fever, or simply
feeling unwell," Beer said via email. "Not only will they probably not
get on the flight — they may even be taken to/required to go to a
'holding facility' where they would have to stay for days until it is
confirmed that it is not caused by Ebola. That is just about the last
place one would want to go."
Liberian officials said last week
that the patient hospitalized in Dallas, Thomas Eric Duncan, did not
report to airport screeners that he had had previous contact with an
Ebola-stricken woman. It is not known whether Duncan knew she suffered
from Ebola; her family told neighbors it was malaria.
The
potential disincentive for passengers to reveal their own symptoms was
echoed by Sheka Forna, a dual citizen of Sierra Leone and Britain who
manages a communications firm in Freetown.
Forna 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 telephone
interview. "You'd be confined to wards with people with full-blown
disease."
On Monday, the White House announced that a review was
underway of existing airport procedures. Frieden and President Obama's
assistant for homeland security and counter-terrorism, Lisa Monaco, said
Friday that closing the U.S. to passengers from the Ebola-affected
countries would risk obstructing relief efforts.
CDC officials
also say that asymptomatic patients cannot spread Ebola. 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?
Russell, who oversaw the Army's research on Ebola, said he found the epidemiological data unconvincing.
The
CDC's Skinner said that while officials remained confident that Ebola
can be spread only by the overtly sick, the ongoing studies would assess
whether mutations that might occur could increase the potential for
asymptomatic patients to spread it.
Peters, whose CDC
team studied cases from 27 households that emerged during a 1995 Ebola
outbreak in Democratic Republic of Congo,
Skinner
of the CDC, who cited the Peters-led study as the most extensive of
Ebola's transmissibility, 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.
"I'm
not going to sit here and say that if a person who is highly viremic …
were to sneeze or cough right in the face of somebody who wasn't
protected, that we wouldn't have a transmission," Skinner said.
The Ebola strain found in
the monkeys did not infect their human handlers. Bailey, who now directs
a biocontainment lab at George Mason University in Virginia, said he
was seeking to research the genetic differences between the Ebola found
in the Reston monkeys and the strain currently circulating in West
Africa.
Though he acknowledged that the means of disease
transmission among the animals would not guarantee the same result among
humans,
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