What to Read Next

Ebola Outbreak: How Worried Should You Be?

July 28, 2014

PHOTO: Dr. Kent Brantly (R) of Samaritan's Purse relief organization is shown in this undated handout photo provided by Samaritan's Purse. Brantly is one of two American health care workers who tested positive for Ebola on July 26, while working in Liberia. (Photo by REUTERS/Samaritan's Purse/Handout)

The worst Ebola outbreak in history has spread across international borders from Liberia to neighboring Sierra Leone and Guinea, and two Americans helping to fight the deadly virus have been infected. Although the risk to the general population outside of West Africa remains extremely low, the ease of modern-day travel poses a challenge for those fighting to contain the outbreak.

"The biggest risk is that an infected person gets on an airplane and flies to the United States," Diane Griffin, MD, professor and chair in molecular microbiology and immunology at Johns Hopkins University, told Yahoo Health. "It's a risk for every country in the world that's connected to West Africa by air travel."

For most parts of the world, Griffin said, recognition and isolation of the cases and implementing necessary precautions will happen very quickly, before the possibility of transmission happens. "The risk to the general population, especially outside of Africa, is essentially nonexistent," she added.

Before the current outbreak, there had been no cases of the virus traveling to another country by airplane. That changed on July 20, when an infected Liberian citizen, Patrick Sawyer, traveled by airliner to Nigeria, where he collapsed upon arrival. The city of Lagos has essentially shut down, and Sawyer has been isolated at a local hospital. No known transmission of the virus has occurred.

Ebola virus disease (EVD) is a severe illness that causes hemorrhagic fevers. According to the World Health Organization, the virus is transmitted to people from wild animals and spreads in the human population through close person-to-person contact. Early symptoms of EVD (often mistaken for the flu) include fever, severe headache, sore throat, muscles aches, and joint pain. As the disease progresses, more severe symptoms — including vomiting, diarrhea, weight loss, and bleeding from the nose, mouth, or ears — occur. There is no cure or vaccine for EVD, and the deadly illness has a fatality rate of 90 percent.

According the WHO, Ebola has infected 1,100 people and killed 660 so far in the current West African outbreak. The lower-than-normal 60-percent fatality rate for this outbreak has been attributed to early identification and treatment of the symptoms (such as administering a saline solution to prevent dehydration). 

Ebola is different from the flu or measles in that being in the same room as an infected person will not necessarily cause transmission. A person has to come in close contact with the virus — specifically through blood, vomit, or excrement — to contract EVD. Most of the transmissions, said Griffin, happen in hospitals where the disease is being treated, or in the home of an infected