Doctors Chastise UN Over Ebola Response as Third American Tests Positive

— -- intro: Another American doctor has tested positive for Ebola in Liberia amid news that aid workers have chastised world leaders for not doing enough to contain the outbreak.

"We cannot cut off the affected countries and hope this epidemic will simply burn out,” Dr. Joanne Liu, president of Doctors Without Borders, told the United Nations on Tuesday. "To put out this fire, we must run into the burning building."

The virus has already killed more than 1,900 people in Liberia, Guinea, Sierra Leone and Nigeria, according to the latest numbers from the World Health Organization. In fact, more than half of all Ebola deaths recorded since the discovery of the virus in 1976 have occurred in the last five months, according to WHO data.

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Here are 11 things you should know about the outbreak as fears continue to mount in Africa and beyond.

quicklist: 1category: What's Happening Now in the Ebola Outbreak title: Another American Tests Positive for Ebolatext: Dr. Rick Sacra, another doctor working for missionary group SIM in Liberia, has tested positive for Ebola.

Sacra was working at ELWA Hospital in Monrovia, but he wasn't treating patients in its separate Ebola isolation facility. He was treating pregnant patients in the maternity ward, which means it's not clear how he became infected, according to SIM.

The doctor, who “immediately isolated himself, has been transferred to the ELWA Ebola ward. He is “doing well and is in good spirits,” according to SIM.

Two other Americans –- Dr. Kent Brantly and SIM missionary Nancy Writebol –- were working with Ebola patients in Liberia when they became infected in late July. They were flown to Emory University Hospital for treatment and discharged on Aug. 19 and 21. They also received the experimental drug ZMapp, but doctors say it’s not clear whether it helped them. media: 25236469

quicklist: 2category: What's Happening Now in the Ebola Outbreak title: Doctors Without Borders Scolds the UNtext: Doctors Without Borders president Dr. Joanne Liu had some strong words for the United Nations on Tuesday, urging its member states to do more to curb the outbreak than protect their own borders.

“Doctors Without Borders ... has been ringing alarm bells for months, but the response has been too little, too late,” Liu said, declaring that the world was “losing” the battle with Ebola.

Doctors Without Borders is “completely” overwhelmed despite doubling its staff over the last month, she said, urging United Nations member states to deploy disaster response teams well versed in bio-hazard containment.

“Health workers on the front lines are becoming infected and are dying in shocking numbers,” Liu said. “Others have fled in fear, leaving people without care for even the most common illnesses. Entire health systems have crumbled.”

She said it is the U.N.’s responsibility to take action.

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quicklist: 3category: What's Happening Now in the Ebola Outbreak title: Nancy Writebol Doesn’t Know How She Got Ebolatext: American Ebola survivor Nancy Writebol, 59, spoke out for the first time today after she was quietly discharged from Emory University Hospital on Aug. 19 and declared Ebola-free.

In an interview with Dr. Richard Besser, ABC News chief health and medical editor, Writebol, a missionary working in Liberia, said she initially thought she’d come down with malaria when her Ebola symptoms started in July. It was her job to “decontaminate” doctors as they left the Ebola isolation unit. She said she was the “mama bear.”