People walk in front of the entrance of the Donka Hospital, where victims of the ebola disease are being treated,
People walk in front of the entrance of the Donka Hospital, where victims of the ebola disease are being treated, Reuters

U.S. health officials on Sunday said the condition of Ebola-stricken American doctor Kent Brantly is improving. Brantly flew in from Africa on Saturday and went straight to Atlanta to a hospital with a special isolation ward. A second American missionary stricken with the deadly virus will arrive on Tuesday.

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

All these as Frieden said CDC has received "nasty emails" plus 100 calls from people blasting him for bringing in Brantly and Writebol back into American soil.

People told him "How dare you bring Ebola into the country!?"

"I hope that our understandable fear of the unfamiliar does not trump our compassion when ill Americans return to the U.S. for care," Frieden said.

Read: 2014 Ebola Outbreak: Afflicted Resort to Witch Doctors; Locals Believe Virus is a Western Conspiracy

Christian charity Samaritan's Purse, Brantly's employer, said the 33-year-old doctor had received a dose of an experimental serum before leaving Liberia. The dose could have helped Brantly to walk with assistance after he was flown on Saturday from Dobbins Air Reserve Base in Georgia to Atlanta.

Brantly is currently confined at Emory University Hospital and is being treated by infectious disease specialists.

"We praise God for the news that Kent's condition is improving," Samaritan's Purse said in a statement.

But Frieden told CBS's Face the Nation it was too soon to predict if Brantly would survive this ordeal.

Nancy Writebol, the second American and a medical missionary, is expected to arrive on Tuesday on a specially equipped medical evacuation plane service by Phoenix Air.

Both Brantly and Writebol got the virus while serving in Liberia as medical missionaries. Writebol was likewise given an experimental serum.

"We're hoping Brantly will continue to improve," Frieden told CBS' Face the Nation. "But Ebola is such a scary disease because it's so deadly. I can't predict the future for individual patients."

Dr Bruce Ribner, unit supervisor at Emory University Hospital, said the patients will be placed in a U.S. medical facility that is highly isolated.

He told CNN the facility has windows. They have also installed an intercom so the staff can interact with the sick without needing to go inside the same room where the patients are.

The medical and pharmaceutical industry has yet to develop a cure against Ebola. Because of this, Ribner said Emory will just employ "supportive care" in treating the patients, which entails monitoring a patient's symptoms, vital signs and organ function. Measures, such as blood transfusions and dialysis, will likewise be made to keep the patients stable.

"We just have to keep the patient alive long enough in order for the body to control this infection," Ribner told CNN.

The virus, passed through direct contact with blood, urine, saliva and other bodily fluids from an infected person, is unlikely to spread in the U.S., Frieden said, simply because the U.S. is better equipped with the medical facility and knowledge how to curb the spread.

"I don't think it's in the cards that we would have widespread Ebola," Frieden said. "So it's not going to spread widely in the U.S. Could we have another person here, could we have a case or two? Not impossible," Frieden said.

"We say in medicine never say never. But we know how to stop it here. But to really protect ourselves, the single most important thing we can do is stop it at the source in Africa. That's going to protect them and protect us."