The Connecticut woman who underwent a face transplant in 2011 after being viciously attacked by a chimpanzee is back in a Boston hospital after doctors discovered her body is rejecting the transplant.

Charla Nash, 62, says doctors have decided to end an experimental drug treatment and put her back on her original medication in the hopes of reversing the rejection.

The brave woman had been taking part in a military-funded experiment in which doctors at Boston's Brigham and Women's Hospital tried to wean her off the anti-rejection drugs she had been taking since the 2011 operation.

'The viability of Charla's face transplant is not in jeopardy. Overall, she is doing well,' Director of Plastic Surgery Transplantation at Brigham and Women's Hospital Dr Bohdan Pomahac said in a statement.

'Charla is currently experiencing a moderate rejection episode, which face transplant patients experience on occasion ... We expect this rejection episode to be resolved within the coming week.'

Nash, who had a double hand transplant at the same time as her facial surgery, is expected to be released from the hospital within the next few days. Doctors had to remove the hands shortly thereafter due to her body rejecting the transplant.

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Charla Nash, 62, underwent a face transplant in 2011 after being attacked by a chimpanzee in 2009. She is back in the hospital after doctors discovered her body is rejecting the transplant. Above she is pictured in 2015

Doctors have decided to end an experimental drug treatment and put her back on her original medication in the hopes of reversing the rejection. Above she is pictured drinking hot coffee through a straw in 2015

The mother-of-one was attacked by Travis (pictured above with her) when she went to help her employer and his owner, Sandra Herold, when he escaped

'I appreciate everyone's concern. I feel perfect. I didn't even know I was having a rejection episode,' Nash said in a statement released by the hospital.

'I gave it my all and know my participation in the study will still be beneficial,' Nash said in a statement to The Associated Press.

'I'd do it all over again, if I could. The men and women serving our country are the true heroes.'

The mother-of-one recently discovered several unusual patches on her face, Nash's publicist, Shelly Sindland, said.

Doctors on Monday did a biopsy and determined her body was rejecting the transplant, she said.

The facial transplant operation was funded by the US military so that more could be learned about how it could help wounded veterans.

Anti-rejection drugs can have serious side effects, and the military funded the experiment in the hopes the alternative treatment could help those needing transplants after returning from war.

The immunosuppression drugs that transplant patients are typically given for the rest of their lives carry such risks as cancer, viral infections and kidney damage.

Travis (pictured above with her) ripped off her nose, lips, eyelids, part of her jaw and hands when she was mauled in 2009

She recently discovered several unusual patches on her face and doctors did a biopsy Monday that determined her body was rejecting the transplant. Doctors are hopeful they can reverse the rejection by putting her back on her original medication

Because of those dangers, many transplants of non-vital body parts, such as thumbs, are not considered worth doing. But doctors say that could change if the drugs don't have to be a lifelong commitment.

The Pentagon, which also paid for Nash's transplant, has provided grants to 14 medical facilities across the US through its hand and face transplantation program. The face and the extremities are the most frequently injured parts of the body in war.

Prior to the face transplant surgery, Nash wore a veiled hat to cover her face after the attack

'I'm just happy I had the chance to help,' Nash said. 'I wish I could have done more. I believe in the power of prayer and appreciate everyone who is praying for me.'

Nash lost her nose, lips, eyelids and hands when she was mauled in February 2009 by her employer's 200-pound pet chimpanzee named Travis in Stamford, Connecticut.

The animal, who appeared in commercials for Old Navy and Coca Cola, was thought to be domesticated since he would open doors, drink wine from a glass, eat at the dinner table, and dress himself.

He even used the computer as his owner, Sandra Herold, treated the chimp as if he were her son.

Travis tried to escape by taking Herold's car keys and attempted to use them on several cars.

Herold, who died in 2010, tried to lure Travis back into the house and gave him an iced tea laced with Xanax.

When Nash, arrived at the house to help, the animal brutally attacked her.

Investigators suggested Travis may have mistook Nash, who was familiar with the chimp, as an intruder after she appeared with a new hairstyle.

The Xanax, which is used for anxiety in humans, may have also fueled Travis' aggression.

Herold stabbed Travis during the attack, but the 70-year-old failed to stop the animal. He was eventually shot to death by the police after he assaulted an officer.

Doctors also had to remove her eyes because of a disease transmitted by the chimp.

She later received new facial features taken from a dead woman. She also underwent a double hand transplant, but it failed when her body rejected the tissue.

Nash is blind after doctors had to remove her eyes because of a disease transmitted by the chimp. She later received new facial features taken from a dead woman in 2011

When she began the experiment involving the suspension of anti-rejection drugs in March, 2015, doctors said it would eventually include other patients and its findings could potentially affect hundreds of thousands of people, military and civilian alike.

Just in March, Nash, who would wear a veil over her head, said the facial transplant had changed her life.

She told CBS Boston: 'It's given me a new life again. It's opened up the world to be out in the public and being part of the world again.'

Nash currently lives in Boston alone but has help from part-time aides. She told the television station that she spends most of her days listening to audio books and exercising.

It hasn't been an easy journey. Nash, a former barrel racer and horse jumper, said in March that she has become increasingly patient because she has had to ask for help instead of doing everything herself.

In her original face transplant surgery, doctors removed the face from the donor (left) including all underlying nerves and muscles (right)

They placed the donor's face on Ms Nash and connected each nerve, muscle and blood vessel

In the interview with CBS Boston, she said that she chooses to look to the future and dreams of living on a farm in a small town once she is finished with her medical tests.

In return for footing her medical bills, the US military requires that she goes in for medical tests every few weeks.

She is subjected to MRIs and CT scans to determine how well her brain is sending signals to her new face. In addition, doctors examine how well the arteries are delivering blood to the transplant.

Nash, who won tickets to the Boston Flower and Garden Show in March, generously passed them on to her nurse as a token of gratitude.

She told CBS: 'When people do so much for you, you wish you could give back to everybody. Whether I can, I'm going to do little by little.'