An American doctor who caught the ebola virus while in Liberia is improving in intensive care in Atlanta after being brought to the U.S. Saturday on a special plane outfitted with a microbial containment center, a top U.S. health official said Sunday, according to a Reuters report.

A second American with ebola is expected to return to the U.S. Tuesday, USAToday reports. An Associated Press video posted on Youtube shows the plane taking off Saturday from Georgia.

And AlJazeera reports that a doctor in the Nigerian capital of Lagos who treated a Liberian ebola victim has tested positive for the virus — the second confirmed case in sub-Saharan Africa’s largest city, authorities said.

Dr. Kent Brantly is being treated by infectious disease specialists at Emory University Hospital and was able to walk, with help, from an ambulance after he was flown Saturday to Atlanta, Reuters reports.

“It’s encouraging that he seems to be improving – that’s really important – and we’re hoping he’ll continue to improve,” said Dr. Tom Frieden, director of the U.S. Centers for Disease Control and Prevention (CDC) in Atlanta.

It’s too soon to predict whether Brantly will survive, Frieden told CBS’s “Face the Nation.”

A 33-year-old father of two young children, Brantly works for  Samaritan’s Purse, a North Carolina-based Christian group. He was in Liberia helping ebola victims when he got sick.

Nancy Writebol, a medical missionary helping treat ebola victims in Liberia, is scheduled to leave the West African nation at 1 a.m. Tuesday on a specially equipped medical evacuation plane, Liberian Information Minister Lewis Brown said, according to the Associated Press and USAToday.

Seventy other people believed to have come into contact with the Liberian Patrick Sawyer are being monitored for ebola, Nigerian Health Minister Onyebuchi Chukwu said Monday, according to AlJazeera. Eight have been placed in quarantine including three who have symptoms. Sawyer died of ebola in Nigeria after taking several plane trips while visibly sick.

The confirmed case “is one of the doctors who attended to the Liberian ebola patient who died,” Chukwu told journalists.

A quarantine unit has been set up in Lagos and blood tests from the three people displaying ebola-like symptoms have been sent for testing, with results expected later Monday, the minister said.

Sawyer, who worked for Liberia’s finance ministry, contracted the virus from his sister before travelling to Lagos for a meeting of West African officials.

He landed in Lagos July 20 from Monrovia after switching planes in Togo’s capital Lome.

He was visibly sick upon arrival and taken directly to the First Consultants hospital in the upscale Lagos neighborhood of Ikoyi. He died in quarantine July 25.

The hospital was closed indefinitely.

The second confirmed case in Nigeria is the latest in the worst-ever ebola outbreak, which has infected 1,440 people and left 826 dead, according to AlJazeera. The other cases are in Guinea, Liberia and Sierra Leone.