Dr Kent Brantly's wife has spoken of the family's relief at his return to the US for urgent Ebola treatment.

The 33-year-old doctor was serving Ebola victims in Liberia with Samaritan's Purse when he became infected with the deadly virus.

He was flown back to the US on Saturday and is being treated in an isolation unit at Emory University Hospital, in Atlanta.

Head of the Centers for Disease Control and Prevention Tom Frieden told Face the Nation on CBS that Dr Brantly "seems to be improving".   

The father of two was also able to spend 45 minutes with his wife, Amber, in protective conditions. 

She and their two children had already returned to the US before Dr Brantly became sick and are not infected with Ebola. 

She said in a statement that the family was "rejoicing" over Dr Brantly's safe arrival and were "confident" in the care he was receiving. 

"I was able to see Kent today. He is in good spirits. He thanked everyone for their prayers and asked for continued prayer for Nancy Writebol's safe return and full recovery," she said. 

In a previous statement she asked people to keep praying for the people of Liberia and those who are still serving there. 

Samaritan's Purse said it had evacuated all but its most essential personnel from the country over the weekend.  

Over 800 people have died as a result of the outbreak of the virus in West Africa, the World Health Organisation has confirmed.  

Writebol, who was serving in Liberia with SIM when she became infected with Ebola, is due to arrive back in the US for treatment on Tuesday.  

The Blaze published excerpts of a touching sermon Dr Brantly gave at his home church, Southeastern Church of Christ in Indianapolis, prior to leaving for Liberia in which he explained his reasons for going to the country with his family. 

"For two years we will live and work and serve among the people who, until the last 10 years of peace, had known nothing but the violence and devastation of war for the previous 20 years," he said.  

"I've never been to Liberia ... It's because God has a call on my life."

He added: "On difficult days, when I want to give up or when I wonder if I've made the right decision, retelling my story reminds me of how God has brought me to where I am."