By Denise Grady
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A
woman in Monrovia, Liberia, passed a man believed to be infected with Ebola.
Researchers say it could take 12 to 18 months to bring the epidemic under
control. Credit Abbas Dulleh/Associated Press
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The deadly Ebola outbreak sweeping across three
countries in West Africa is likely to last 12 to 18 months more, much longer
than anticipated, and could infect hundreds of thousands of people before it is
brought under control, say scientists mapping its spread for the federal
government.
“We
hope we’re wrong,” said Bryan Lewis, an epidemiologist at the Virginia
Bioinformatics Institute at Virginia Tech.
Both
the time the model says it will take to control the epidemic and the number of
cases it forecasts far exceed estimates by the World Health Organization,
which said last month that it hoped to control the outbreak within nine months
and predicted 20,000 total cases by that time. The organization is sticking by
its estimates, a W.H.O. spokesman said Friday.
But researchers at various universities say that
at the virus’s present rate of growth, there could easily be close to 20,000
cases in one month, not in nine. Some of the United States’ leading
epidemiologists, with long experience in tracking diseases such as influenza,
have been creating computer models of the Ebola epidemic at the request of the
National Institutes of Health and the Defense Department.
The Centers
for Disease Control and Prevention declined to comment on the projections.
A spokesman, Tom Skinner, said the agency was doing its own modeling and hoped
to publish the results soon. But the C.D.C. director, Dr. Thomas R. Frieden,
has warned repeatedly that the epidemic is worsening, and on Sept. 2 described
it as “spiraling out of control.”
While
previous outbreaks have been largely confined to rural areas, the current
epidemic, the largest ever, has reached densely populated, impoverished cities
— including Monrovia, the capital of Liberia — gravely
complicating efforts to control the spread of the disease. Alessandro
Vespignani, a professor of computational sciences at Northeastern University
who has been involved in the computer modeling of Ebola’s spread, said that if
the case count reaches hundreds of thousands, “there will be little we can do.”
What
worries public health officials most is that the epidemic has begun to grow
exponentially in Liberia. In the most recent week reported, Liberia had nearly
400 new cases, almost double the number reported the week before. Another grave
concern, the W.H.O. said, is “evidence of substantial underreporting of cases
and deaths.” The organization reported on Friday that the number of Ebola cases
as of Sept. 7 was 4,366, including 2,218 deaths.
“There
has been no indication of any downturn in the epidemic in the three countries
that have widespread and intense transmission,” it said, referring to Guinea, Liberia and Sierra Leone.
The scientists who produced the
models cautioned that their dire predictions were based on the virus’s current
uncontrolled spread and said the picture could improve if public health efforts
started to work. Because conditions could change, for better or for worse, the
researchers also warned that their forecasts became shakier the farther into
the future they went.
Dr. Lewis, the Virginia Tech epidemiologist, said
that a group of scientists collaborating on Ebola modeling as part of an
N.I.H.-sponsored project called Midas, short for Models of Infectious Disease Agent Study, had come
to a consensus on the projected 12- to 18-month duration and very high case
count.
Another
Midas participant, Jeffrey L. Shaman, an associate professor
of environmental health sciences at the Columbia University Mailman School
of Public Health, agreed.
“Ebola
has a simple trajectory because it’s growing exponentially,” Dr. Shaman said.
Lone
Simonsen, a research professor of global health at George Washington University
who was not involved in the modeling, said the W.H.O. estimates seemed
conservative and the higher projections more reasonable.
“The final death toll may be
far higher than any of those estimates unless an effective vaccine or therapy
becomes available on a large scale or many more hospital beds are supplied,”
she said in an email.
Dr. Vespignani said that the W.H.O. figures would
be reasonable if there were an effective campaign to stop the epidemic now, but
that there is not.
The
modeling estimates are based on the observed growth rate of cases and on
factors like how many people each patient infects. The researchers use the past
data to make projections. They can test their methods by, for instance, taking
the figures from June, plugging them into the model to predict the number of
cases in July, and then comparing the results with what actually happened in
July.
Dr. Shaman’s research team created a model that estimated the
number of cases through Oct. 12, with different predictions based on whether
control of the epidemic stays about the same, improves or gets worse. If
control stays the same, according to the model, the case count by Oct. 12 will
be 18,406. If control improves, it will be 7,861. If control worsens, it will
soar to 54,895.
Before
this epidemic, the largest Ebola outbreak was
in Uganda from 2000 to 2001, and it involved only 425 cases. Scientists say the
current epidemic surged out of control because it began near the borders of
three countries where people traveled a lot, and they carried the disease to
densely populated city slums. In addition, the weak health systems in these
poor countries were not equipped to handle the disease, and much of the
international response has been slow and disorganized.
But questions have also been raised about whether
there could be something different about this strain of Ebola that makes it
more contagious than previous ones.
Researchers are doubtful, but Thomas W. Geisbert,
an Ebola expert at the University of Texas Medical Branch in Galveston, said it
was important to keep an open mind about the possibility. During vaccine tests
expected to start next month in monkeys, he said, he and his colleagues will
monitor infected animals to see if they develop unusually high virus levels
early in the disease that might amplify its infectiousness.
Some
scientists have also suggested that as the outbreak continues and the virus
spreads from person to person, it will have more opportunities to mutate and
perhaps become even more dangerous or contagious. But Stuart T. Nichol, chief
of the C.D.C.’s Viral Special Pathogens Branch, said that so far, researchers
monitoring the mutations had seen no such changes.
Source: http://www.nytimes.com
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