This photo provided by Jeremy Writebol shows his mother, Nancy Writebol, with children in Liberia on Oct. 7. Nancy Writebol has since been diagnosed with Ebola virus. (Associated Press/Courtesy Jeremy Writebol)

A second American infected with the Ebola virus will leave Liberia for the United States in the early morning hours on Tuesday (Monday night Eastern Standard Time), a Liberian official told Reuters.

Nancy Writebol, a missionary from Charlotte, N.C., will be transported in the same aircraft that brought an Ebola-stricken doctor, Kent Brantly, back to the United States from Liberia over the weekend.

The “air ambulance” equipped with a Aeromedical Biological Containment System — a type of portable isolation unit — will transport Writebol to Atlanta. The unit is equipped with a HEPA-filtered ventilation system, and drugs and fluid will be administered using needleless IVs.

Both Writebol and Brantly were aid workers with Samaritan’s Purse, an international relief organization. Smaritan’s Purse has since evacuated all but essential personnel from Ebola-stricken countries, the group said in a statement.

Writebol may have been exposed to the virus while working to decontaminate people coming in and out of a Liberian Ebola treatment unit, according to Reuters.

Once infected, someone with Ebola becomes contagious when symptoms begin to show. The disease causes fever, pain and sometimes internal and external bleeding and organ failure.

There is no cure. However, several potential vaccinations are being developed.

According to an NBC News report that cited family members, Brantly has received a dose of an experimental Ebola treatment.

Brantly, who is being treated in a state-of-the-art isolation facility at Emory University Hospital in Atlanta, is showing signs of improvement, Tom Frieden, director of the U.S. Centers for Disease Control and Prevention, said Sunday.

An ambulance arrives with Ebola victim Dr. Kent Brantly, right, to Emory University Hospital, Saturday, Aug. 2, 2014, in Atlanta. Brantly, infected with the Ebola virus in Africa arrived in Atlanta for treatment Saturday, landing in a specially equipped plane at a military base, then being whisked away to one of the most sophisticated hospital isolation units in the country, officials say. (AP Photo/WSB-TV Atlanta) Ebola patient Kent Brantly (right) arriving at Emory University Hospital. (Associated Press/WSB-TV Atlanta)

Brantly was seen walking, with assistance, from an ambulance to the hospital in a full-body hazmat suit.

In Africa, the worst-ever outbreak of the deadly disease continues to ravage Liberia, Guinea and Sierra Leone. The World Health Organization reported 826 deaths as of July 30.

On Monday, Nigerian officials announced a second case of Ebola in Lagos, Africa’s largest city, Reuters reported. Nigeria’s health minister Onyebuchi Chukwu said that a doctor who treated Patrick Sawyer — who died in Lagos after flying there from Liberia — “has tested positive” for the virus.

As the worst Ebola outbreak in history unfolds in West Africa, The Post's Joel Achenbach explains how the deadly virus wreaks havoc on the human body. (Davin Coburn/The Washington Post)