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, according to 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 that the computer model estimates 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 WHO spokesman said Friday.
But researchers at various universities said that at the virus' present rate of growth, there could easily be close to 20,000 cases in one month, not in nine. Some of the leading U.S. 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. A spokesman, Tom Skinner, said the agency was doing its own modeling. But the CDC director, Dr. Thomas Frieden, warned earlier this month that the outbreak was "spiraling out of control.
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While previous episodes have occurred in rural areas, the current epidemic, the largest ever, has reached densely populated cities, including Monrovia, the capital of Liberia. Alessandro Vespignani, a professor of computational sciences at Northeastern University who has been involved in the Ebola modeling, said that if the case count reaches hundreds of thousands, "there will be little we can do."
The biggest worry is that the epidemic has begun to grow exponentially in Liberia. In the most recent week reported, Liberia had about 400 new cases, almost double the number reported the week before. Another grave concern, the WHO said, is "evidence of substantial under reporting of cases." The organization reported 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' current uncontrolled spread. 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.
Lewis, the Virginia Tech epidemiologist, said that a group of scientists collaborating on Ebola modeling as part of an NIH-sponsored project called Midas, short for Models of Infectious Disease Agent Study, had come to a consensus on the high case count.
Another Midas participant, Jeffrey 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," Shaman said.
Lone Simonsen, a research professor of global health at George Washington University who was not involved in the modeling, said the WHO estimates seemed conservative and the higher projections more reasonable.
"The final death toll may be far higher than any of those estimates," she said in an email. Vespignani said that the WHO 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 such as how many people each patient infects.
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.
But questions have been raised about whether there could be something different about this strain of Ebola that makes it more contagious.
Researchers are doubtful, but Thomas 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. He said that 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.
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