PHOTOS: Ebola outbreak in Africa

The spread of the deadly Ebola virus has prompted the Peace Corps to evacuate volunteers from three West African countries, the organization announced today.

Two Peace Corps volunteers been placed in isolation after being exposed to someone who later died of the highly contagious virus, according to an agency spokeswoman. While not showing symptoms, the volunteers are awaiting medical clearance to return to the United States. CBS News reports the volunteers are in Liberia. The Ebola virus is spread via direct contact with bodily fluids, and people are considered contagious when they start showing symptoms. It can take as long as 21 days before a person infected with the virus starts showing symptoms, according to the World Health Organization.

While the Centers for Disease Control and Prevention has said that the odds that Ebola will reach the United States are slim, it has still advised American health-care workers to be cautious. "The likelihood of this outbreak spreading outside of West Africa is low,” Stephan Monroe, deputy director of CDC's National Center for Emerging and Zoonotic Infectious Diseases, said on a conference call with reporters Monday. But, he added, "the CDC has to be prepared for the remote possibility.”

The Peace Corps will temporarily remove its 102 volunteers in Guinea, 108 in Liberia and 130 in Sierra Leone. The group had previously released a statement saying that it was monitoring the outbreak in consultation with the CDC and the State Department.

The CDC has issued a Level 2 travel health alert in response to the outbreak. The agency has advised U.S.-based health-care workers to be aware of the symptoms of Ebola and the travel histories of their patients.

Health-care workers are among the most vulnerable to the virus. Sierra Leone's top Ebola doctor fell victim to the virus and died. Two American health-care workers, volunteers with the Christian aid group Samaritan’s Purse, have contracted the virus. The group has since evacuated some workers from Liberia, but medical staff have been left behind to treat patients.

Fear of Ebola's spread, which is concentrated in West Africa, has gone global, with officials as far away as Hong Kong taking precautionary measures. Nearly 700 people have died in what the World Health Organization has classified as the largest outbreak on record.

Update: This post has been updated to reflect that CBS has reported that the two Peace Corps volunteers placed in isolation are in Liberia.