Ebola Likely to Spread Internationally; Modest Risk for US, UK

Larry Hand

September 11, 2014

Unless the Ebola outbreak in Nigeria is promptly contained, Ebola virus disease (EVD) is likely to spread internationally, with Ghana, the United Kingdom, and Gambia being the countries most likely to be next in line, according to an article published online September 2 in PLOS Currents.

Belgium, the United Kingdom, France, and the United States are the countries projected to have more than a modest risk (<5%) for case exportations through international travel from the most affected countries, according to researchers who modeled the potential spread of EVD.

"I would say this is good news at the moment, in the sense that our system should be pretty well equipped to cope with importation events," senior author Alessandro Vespignani, PhD, Sternberg Distinguished University Professor of Physics at Northeastern University in Boston, Massachusetts, told Medscape Medical News in a telephone interview. "Actually, in our country, we should be able to contain it. We do not expect to see a large number of cases."

To estimate EVD spread, Marcelo F.C. Gomes, PhD, from the Laboratory for the Modeling of Biological and Socio-Technical Systems, which Dr. Vespignani directs at Northeastern University, and colleagues analyzed data from the World Health Organization's Disease Outbreaks News.

The researchers used the university's Global Epidemic and Mobility Model (GLEaM) to divide the world population into geographic census areas defined around transportation hubs. They integrated those data with data from the Socioeconomic Data and Application Center (SEDAC) at Columbia University in New York City and analyzed data from the International Air Transportation Association and Official Airline Guide databases.

Current Pace

"We evaluate the progression of the epidemic in West Africa and its international spread under the assumption that the EVD outbreak continues to evolve at the current pace," the researchers write. "The numerical simulation results show a steep increase of cases in the West Africa region, unless the transmissibility of the EVD is successfully mitigated."

The researchers considered Sierra Leone, Guinea, and Liberia as the baseline countries. Nigeria and Senegal have since reported cases of EVD.

According to the World Health Organization's August 28 update, the total number of probable and confirmed cases of EVD for the baseline countries and Nigeria stood at 3069, and the number of related deaths stood at 1552.

Senegal's Ministry of Health reported 1 case at the end of August. In the researchers' models, that country was the seventh most likely to have imported a case of EVD by September.

Growing Probability

"It's crucial for countries like the US and those in Europe to always screen people with a history that could point to Ebola, but everybody at this point is so aware of the disease that I don't think this is a problem," Dr. Vespignani told Medscape Medical News.

He continued, "At this point, it's not just a remote probability that somebody coming from those regions is infected with Ebola, although there is a small probability."

The researchers project that the risk of importing at least 1 EVD case into the United States would increase from about 5% to 20% to 25% between September 1 and September 22.

"Probability tends to grow according to the exponential growth rate of the disease. Unfortunately, this is a problem with epidemics when they start to grow exponentially. This is why we think that the battle at the moment is in Africa. We need to contain and extinguish the fire there."

The United States is one of the countries likely to get cases, he said. "What we also see from our modeling is that the number of cases that we would get here if somebody comes with the disease would be very small."

This research was supported by Models for Infectious Disease Study grant from the National Institute of General Medical Sciences. The authors have disclosed no relevant financial relationships.

PLOS Currents. Published online September 2, 2014. Full text


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