Christian humanitarian organisation Serving in Mission (SIM) announced Tuesday that another of its doctors has contracted the deadly Ebola virus.

The doctor, identified as Rick Sacra, is the second SIM physician diagnosed with the virus.

SIM operates the Eternal Love Willing Africa (ELWA) Hospital in Monrovia, Liberia, which has an isolation ward to treat patients infected with Ebola. The recently diagnosed doctor was working with pregnant women at ELWA, and not with Ebola patients. It is unknown how the doctor became infected.

The SIM physician isolated himself after exhibiting symptoms of Ebola infection, and is being treated in ELWA's quarantined unit. SIM President Bruce Johnson said he was deeply troubled by the news.

"My heart was deeply saddened, but my faith was not shaken, when I learned another of our missionary doctors contracted Ebola," he said in a statement.

"As a global mission, we are surrounding our missionary with prayer, as well as our Liberian SIM/ELWA colleagues, who continue fighting the Ebola epidemic in Liberia. We have gifted Liberian doctors, medical staff and support staff who are carrying on the fight."

Dr Kent Brantley of SIM sister organisation Samaritan's Purse was diagnosed with the Ebola virus in July after treating patients at ELWA's isolation ward. Nancy Writebol, another SIM humanitarian worker, also contracted the virus at ELWA.

The two were medically evacuated to the United States last month, and no longer have traces of the virus in their blood. They were released from Emory University Hospital nearly two weeks ago.

Dr Brantly told reporters that he was saddened by the news of the new Ebola infection, and is praying for the SIM physician.

"I was notified about [the infection] this morning," he told NBC News on Tuesday. "I spent a good long while tearful, in prayer." Brantly reported that he was "very close" to the infected physician.

The 33-year-old also said that he has been sustained by prayers from around the world, and is still in need of intercession.

"Right now I still have a lot of recovering to do," Brantly said. "I know I look well but I am still pretty weak."

The Ebola outbreak began in Guinea in February, and quickly spread to Sierra Leone and Liberia. The World Health Organisation reported 1,552 deaths from the virus as of August 28.