American military dogs are having to be treated for post-traumatic stress disorder after serving in Iraq and Afghanistan.

The illness is well-documented among servicemen and women returning from wars but its existence in animals is less clear-cut.

"There is a condition in dogs which is almost precisely the same, if not precisely the same, as PTSD in humans," said US vet Nicholas Dodman .

But some vets dislike applying the diagnosis to animals, thinking it demeans servicemen and women, he said.

The military defines PTSD as a condition that develops after a life-threatening trauma. Victims suffer three types of experiences long afterward, even in a safe environment. They repeatedly re-experience the trauma in nightmares or vivid memories. They avoid situations or feelings that remind them of the event, and they feel keyed up all the time.

Gina was a playful two-year-old German shepherd when she went to Iraq as a highly trained bomb-sniffing dog, conducting door-to-door searches and witnessing all sorts of noisy explosions.

She returned home to Colorado cowering and fearful. When her handlers tried to take her into a building, she would stiffen her legs and resist. Once inside, she would tuck her tail beneath her body and slink along the floor. She would hide under furniture or in a corner to avoid people.

A military vet diagnosed with her PTSD.

"She showed all the symptoms and she had all the signs," said Master Sgt. Eric Haynes, the kennel master at Peterson Air Force Base. "She was terrified of everybody and it was obviously a condition that led her down that road."

A year later, Gina is on the mend. Frequent walks among friendly people and a gradual reintroduction to the noises of military life have begun to overcome her fears, Sgt. Haynes said.

The dog had been assigned to an Army unit, and her job was to search for explosives after soldiers entered a house. The troops sometimes used noisy, blinding stun grenades and kicked down doors and Gina was once in a convoy when another vehicle was hit by an improvised bomb.

Back home at Peterson, Gina wanted nothing to do with people.

Mr Dodman said he doubted Gina could recover completely.

"It's a fact that fears once learned are never unlearned," he said. "The best thing you can do is apply new learning, which is what (Gina's handlers are) doing," he said.