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(CNN) -- They listen to tales of life's worst moments, but they can't go home and tell their spouses about what they've heard. Sometimes no amount of schooling is enough to shield them from taking on some of their patients' suffering.
Those who counsel trauma victims -- whether they be psychiatrists, social workers or advocates -- can experience an emotional toll after intensive exposure to patients' stories of horror. Experts call this phenomenon "vicarious trauma."
The impact of trauma on those who help the traumatized has become a subject of discussion as investigators try to piece together why Maj. Nidal Malik Hasan, 39, an Army psychiatrist at Darnall Army Medical Center, allegedly opened fire at a military processing center Thursday at Fort Hood Army Post in Texas, killing 13 people and wounding 30 others.
As an army psychiatrist, Hasan worked to help others in high-stress situations, including victims of post-traumatic stress disorder, military officials said. He is a graduate of Virginia Tech and previously worked at Walter Reed Army Medical Center. He had never deployed outside the United States, but was scheduled to go to Afghanistan, officials said.
The symptoms of vicarious trauma -- stress, social withdrawal, sensitization to televised violence -- are not enough to make people violent themselves, said Barbara Rothbaum, director of the Trauma and Anxiety Recovery Program at Emory Medical School.
"People do have their own stress reactions, especially people who maybe shouldn't be in the field," Rothbaum said. "That's not going to predispose someone to homicide."
The symptoms of vicarious trauma, also called secondary traumatic stress, parallel those of direct trauma, said Laurie Anne Pearlman, former president of the Trauma Research, Education, and Training Institute Inc. and author of several books about vicarious trauma.
"In working with victims of violence, there's a lot of anguish and grief and pain and sorrow," she said. "It really affects your own emotional life."
Helpers of victims may begin to feel they can't enjoy life when so many people in the world are suffering, she said. Hearing stories of betrayal may cause some to distrust their close contacts or become overprotective of their children. Mental health professionals are generally obligated not to share patient information with anyone, so they can't seek comfort from friends or family about a patient experience.
Listening to patients who have suffered, therapists may have so much empathy that they develop what is called "compassion fatigue."
But vicarious trauma goes beyond that, said Dr. Frank Ochberg, former associate director of the National Institute of Mental Health. "It's not that I am feeling sorry for them and empathize with them, it's that I'm becoming them," he said. This vicarious or secondary traumatic stress is relatively rare, but "we've all identified it," he said.
The toll of bearing witness to accounts of others' suffering can take many forms. Rothbaum recalls one therapist involved in a rape victim study many years ago. She was married and a "very together woman," Rothbaum said, who nonetheless said, "after hearing all these stories, I'm starting to get angry at men." Ochberg recalls a colleague who worked with Vietnam veterans telling of his own dreams of his patients' conflicts, traumas and tragedies.
In hiring mental health professionals, there is some assumption of pre-selection. Attaining advanced degrees in the field and recommendations from jobs and internships indicate a certain preparedness for dealing with patients, Rothbaum said.
When Rothbaum interviews therapists for treating post-traumatic stress disorder, she makes sure they know what they're getting into.
"I do specifically talk to them about, you know, you will hear the worst thing you've ever heard. You will hear life's worst moments. You will hear incidents of pure evil," she said. "People are pretty clear about, 'Yeah, I think I can handle it,' or 'No, this job isn't for me.' "
Experts say therapists should follow their own advice in helping themselves deal with this suffering -- have a strong support network of friends, family, and co-workers, stay physically fit, and eat well. Getting involved in social action of some sort is also very useful, as it leads people to feel they are doing something on a larger level, Pearlman said. It's important for those who help trauma victims with their problems to seek help themselves from other professionals when they need it, Ochberg said.
"I would find myself, when troubled, talking to my boss, who was the mental health director of the country," he said.
Sometimes burnout from dealing with trauma victims can necessitate a leave of absence, sometimes permanently, from a job, Ochberg said.
"I have many people who contact me informally and sometimes formally for help with trauma, tragedy and a feeling that they're about at their capacity as providers of services to continue to provide services," he said.