An American missionary who contracted Ebola in Liberia says "we're living in a spiritual battle for people's lives".

Speaking to Christianity Today, Nancy Writebol spoke of her personal struggle with the disease, and the "dark days" she went through as she was fighting for survival.

"I don't know that I ever asked 'Why, God?' or 'Why?' I know that I received peace from the Lord...All of us in Liberia felt that the week that Dr Brantly and I were really struggling, there was a spiritual battle going on – there were some very, very dark days," she said.

"But also in the darkness, the Lord brought back into my mind his Word and his peace."

Writebol and her husband David were working with Ebola patients in Monrovia through the Serving in Mission [SIM] humanitarian group when she became infected.

Miraculously, she survived after being flown back to the US for experimental treatment, but says that it has been a "wrestle" to understand how she has been able to live while so many others have died.

"We don't know the mind of God and why the Lord allowed me to survive and some of my African brothers and sisters not to survive. I just have to say that God is so great, and that we don't know his mind and we don't want to put him in a box," she said.

"We give God glory for those who are surviving. But it's like cancer or any disease: some survive and some don't. I trust the Lord in what he's doing and how he's working."

Despite their ordeal, the Writebols may return to Liberia next year, though Nancy said they would need to take "serious precautions".

"Liberia is where God called us. We truly care about our West African brothers and sisters and what they are experiencing," she said.

"It's a spiritual issue. We're living in a spiritual battle for people's lives and for people to come to know Christ as their Saviour."

The latest figures from the World Health Organisation [WHO] indicate that 4,447 people have now died from Ebola, though some agencies are suggesting that the true figure could be significantly higher.

The outbreak has been worst in Liberia, Sierra Leone and Guinea, and there are concerns that it could spread to the West. However, WHO director of strategy Christopher Dye has assured that the likelihood of a "major outbreak" in the West is low.

"The possibility that once an infection has been introduced that it spreads elsewhere, is something that everybody is going to be concerned about," he said.

"We're confident that in North America and Western Europe where health systems are very strong, that we're unlikely to see a major outbreak in any of those places."