Panic over the spread of Ebola has been growing in Europe, North America, and Asia after the world saw the first three patients diagnosed with the disease outside of West Africa: two in Texas and one in Spain.

We're not likely to see an outbreak in the US, but now that the disease has been transmitted here, Americans are increasingly worried. Nina Pham, a 26-year-old nurse who cared for Ebola patient Thomas Eric Duncan in Dallas, was recently diagnosed with the disease. Duncan died in Dallas last week.

And although the threat of widespread transmission in the US is very low, air travel makes it very likely that Ebola cases could arrive here again and may start popping up in other countries.

"Germs have always traveled. The problem now is they can travel with the speed of a jet plane," Howard Markel, a professor of the history of medicine at the University of Michigan, told The New York Times.

Researchers at the Laboratory for the Modeling of Biological and Socio-Technical Systems at Northeastern University in Boston calculated which countries are most at risk for imported cases of Ebola by the end of October, as shown in the below chart:

The US, Senegal, and Nigeria have all seen at least one imported case already. MOBS Lab

Keep in mind that this is the risk of a single imported case, not the risk of an outbreak. To get these projections, the MOBS Lab looked at air travel and commuting patterns originating in the affected region.

These projections change based on how much travel from the affected region is reduced due to Ebola. The chart above shows projections with no reduced travel. "Severe travel restrictions to and from the affected areas (80% airline traffic reduction) generates only a 3-4 weeks delay in the international spreading," the researchers noted. And such restrictions would make the outbreak worse for everyone.

The MOBS researchers take care to emphasize that widespread outbreaks in most of the countries shown in the chart are highly unlikely. A "large outbreak involving more than 10 individuals, although potentially possible, can be considered as very rare events," they write. The data suggests that "effective management and isolation of cases is keeping the number of [Ebola] cases to deal with to a very limited number, lowering the risk of losing control of the outbreak."

Ebola has been ravaging parts of West Africa over the past few months in part because the region's healthcare system is not equipped to contain the disease.

So far, Ebola hasn't spread much outside of the epicenter of the outbreak. Spain was the first country outside of Africa with a locally acquired case. The US has seen one local transmission so far — the Dallas nurse — and one death from someone who contracted the disease in Liberia and then started showing symptoms after he traveled to the US to visit family and friends.

More than 4,000 people have died in what's been the worst Ebola outbreak the world has ever seen. More than 8,000 people have contracted the disease in Guinea, Liberia, and Sierra Leone. Those numbers include 401 healthcare workers who have been infected; 232 of them have died.

As long as the outbreak rages on in West Africa, "we can't make the risk zero here," CDC Director Tom Frieden has said. "We wish we could."

Ebola has killed more than half of those infected in the current outbreak. The disease begins with flu-like symptoms and in many cases escalates to internal and external bleeding and organ failure.