In a startling new report published this week in the journal PLOS Currents: Outbreaks, a team of experts says that Ebola will likely make its way to the US, estimating there is a 20 percent chance this could happen by the end of this month. While the US health care system is well-equipped to handle the virus and is expected to halt transmission, limiting outbreaks to isolated cases, the findings are an alarming reminder of the massive reach of the deadly virus.
According to the World Health Organization (WHO), as of September 4 at least 3,685 people across several West African nations have been infected with Ebola during the current outbreak. With a death toll that just surpassed 1,900, the 2014 outbreak has now killed more people than all previous outbreaks combined. And despite the best efforts of the affected countries, the outbreak shows no sign of slowing down: In a situation assessment released on Monday, the WHO warned that the number of Ebola cases is “increasing exponentially.” The circumstances in Liberia are particularly dire, says the WHO:
As soon as a new Ebola treatment facility is opened, it immediately fills to overflowing with patients, pointing to a large but previously invisible caseload. Many thousands of new cases are expected in Liberia over the coming three weeks.
The general consensus among experts is that the deadly outbreak will likely get far worse before it gets better. Recent studies using disease-modeling techniques indicate that as many as 10,000 cases of Ebola virus disease could be detected by the end of the month – and potentially hundreds of thousands more after that.
Ebola is transmitted via contact with the bodily fluids of an infected person, and it can take up to 21 days after infection for symptoms to appear. These symptoms include fever, muscle weakness and sore throat, and later vomiting, rash and bleeding.
There is no clinically available vaccine for Ebola, nor are there any approved treatments. While scientists are making great strides towards developing new methods to prevent and treat Ebola, the process of drug development is slow and experts say it is unlikely that the current outbreak will be culled with a medication.
Analysis compares international travel patterns with rate of transmission
In the new analysis, researchers compared international travel patterns with estimates on the rate of transmission to calculate the speed at which Ebola might spread to different regions of the globe. The team created a disease model using parameters from the current outbreak, such as funeral and community transmission dynamics, as well as characteristics of the affected geographical regions, which they then used to predict future disease spread:
Air traffic connections from West Africa to the rest of the world: While Guinea, Liberia and Sierra Leone don’t have many flights outside the region, Nigeria is well-connected to Europe and the U.S., which greatly increases the risk of international transmission of Ebola.
Using a series of microsimulations generated by the disease models, the team calculated the probability of Ebola transmission in currently unaffected countries, both within and outside of Africa, over the next several weeks. The researchers note that their estimates are based on the rate of transmission at the time of analysis; since that rate has increased rapidly in recent weeks, the results could underestimate the actual risk of transmission, the team says.
The results of the modeling simulations showed that the disease will likely spread first to currently unaffected African countries, before eventually expanding beyond Africa’s borders. “The extension of the outbreak is more likely occurring in African countries, increasing the risk of international dissemination on a longer time scale,” the team writes.
Although there is not a high level of international travel between some of the affected countries — such as Liberia and Sierra Leone — the researchers say Ebola could spread beyond Africa via Nigeria. This is because Nigeria, where the outbreak has also spread, has many international travel links. An estimated 6,000 passengers fly from Nigeria to the US every week.
Ghana, the United Kingdom, and the United States are among the countries most likely to have an introduced case, according to the model. Senegal, which reported its first Ebola case last week, was in the top ten countries, too:
The risk of importing Ebola into the U.S. will jump dramatically in September, the researchers found.
The researchers say that as the outbreak affects more metropolitan areas with international airports — such as Dakar, the capital of Senegal, where Ebola has spread to in the past week — it becomes more likely that people who do not know they are infected with the virus will spread Ebola to other countries and continents. The assumption that preventing international air travel would halt the outbreak is also challenged in the report, which demonstrates that in reality, such measures would have little effect. Reducing air travel by as much as 80 percent would only temporarily (about 3-4 weeks at the most) prevent the spread of Ebola, the team found.
“Studies have shown the quarantining of entire villages and countries is highly ineffective, and this analysis shows that yet again,” says co-author Dr. Ira Longini, PhD, professor of biostatistics in the University of Florida colleges of Medicine and Public Health and Health Professions. “Surveillance and containment, which includes the isolation of cases and quarantine of close contacts, is the only intervention strategy that works that is available.”
The current risk of the virus spreading to additional countries is described by Dr. Longini and colleagues as “moderate,” but these risks will grow as the virus continues to defy containment, they explain. With time, importation of the virus into the US is “almost inevitable,” the researchers told NPR. However, it is highly improbable that the US would experience widespread transmission, says Dr. Longini: “We would assume that the US would have sufficient capacity to test people and treat them. We would not expect any real transmission in the US.”
The best way to prevent international transmission is to focus on the areas currently affected. Not only does the risk of widespread transmission increase as the outbreak continues, but so does the risk that an acquired mutation will render the disease even more deadly. A recent genetic analysis of the Ebola strain behind the current outbreak found that the virus has already acquired more than 300 unique mutations that differentiate it from previous strains.
Unfortunately, many of the countries hardest hit by the outbreak are still lacking in basic medical supplies like protective gloves and clean needles. Experts say the global response to the outbreak has been “disastrously inadequate,” leading to untold numbers of preventable deaths and contributing to the ongoing spread of the infection. Without an immediate change in the current landscape, the worst is yet to come, experts warn. “The level of outbreak is beyond anything we’ve seen—or even imagined,” said Dr. Thomas Frieden, director of the Centers for Disease Control and Prevention (CDC). In a statement last week, Dr. Frieden urged the global community to join Africa in its fight to overcome the devastating outbreak. “This isn’t just the countries’ problem,” he said. “It’s a global problem.”
“The epidemic just continues to spread without any end in sight,” adds Dr. Longini. “The cat’s already out of the box – way, way out.”