File photo: Like people, animals react to trauma in many different ways. Washington Post photo by Katherine Frey

In the early hours of the last day of May, one of the hugest explosions ever to shake Afghanistan resounded across the capital city of Kabul. The impact of the tanker truck bombing, an insurgent attack that claimed more than 150 lives and injured at least 700 others, was felt several miles away.

The explosion broke windows and cracked ceilings a mile and a half from the blast's epicenter in a central area near embassies and the presidential palace. My house is located in that periphery, and I woke to the thunderous sound and the shaking of windows and walls. I was unhurt, and there was no lasting damage to my home, but the experience was difficult to get over. Although I have lived and worked as a journalist in Afghanistan for three years, I have found that one never gets used to violent conflict.

But as strenuous as it was for me, it seemed to be even more so for my cat, Lola. About 20 minutes after the blast, I found her hiding in the bathroom, cowering behind the radiator. It took almost an hour of petting and hugs to calm her down. This was, after all, one of the biggest explosions Afghans had ever experienced - and that included Lola, who was a kitten when I found her in my garden the year before.

For the next week, Lola seemed edgy. Small sounds would startle her, and she followed me everywhere. She would caterwaul when I left the house and be clingy when I returned. She was eating less and losing weight. It took me a while to realize she might not be only physically unwell. Could Lola, I wondered, have post-traumatic stress disorder?

She certainly wasn't the first animal to be visibly shaken by one of Afghanistan's violent attacks. Hannah Surowinski, the director of an animal shelter in Kabul called Nowzad, told me she frequently sees the sort of anxiety and stress that I was observing in Lola.

"Like people, animals react to trauma in many different ways," Surowinski said. "How it presents itself in that animal is individual to them,"

The US military has seen this reaction to stress in its working dogs. Its veterinarians say that about five percent of those that have served in Afghanistan and Iraq suffer from "canine PTSD," which can make some dogs aggressive, timid or unable to do their jobs.

The diagnosis, known as C-PTSD, is still debated among some in the veterinary field. But research on PTSD in animals is growing, said Stacy Lopresti-Goodman, an associate professor of psychology at Marymount University in Arlington, Virginia. She has studied the topic for much of the past decade, and she told me there is good reason to believe that Lola and other critters might respond to trauma in the same ways people do.

"Given similarities in brain structures responsible for stress responses, animals exhibit symptoms which resemble those of PTSD in humans," she explained.

Lopresti-Goodman pointed to her own research on hundreds of chimpanzees used in biomedical research, about one-quarter of which displayed symptoms of PTSD for years after their retirement. Scholars have also documented PTSD symptoms in parrots that were captured in the wild, kept as pets and then abandoned.

Others have detected such symptoms in African elephants. One 2013 study focused on complex, kin-based groups of elephants in two national parks in Kenya and South Africa that had witnessed "disruptive" events such as mass culling, poaching, translocation to other areas or captures of their species. Some, the researchers wrote, displayed behaviors similar to PTSD in humans.

Much like in humans, though, symptoms of stress and anxiety in animals can differ for every animal - and, of course, the patients cannot describe them. But Lopresti-Goodman said they are observable reactions to events and objects that might remind the animal of the traumatizing event.

Some animals might pace, weave their heads back and forth, bite themselves or even eat their own feces, she said. Other signs are self-calming techniques, such as excessive licking, rocking or hiding. So is what any pet owner might chalk up to depression - a loss of interest in socializing, eating or playing.

Lola, for her part, is doing better. My housemate and I no longer leave her alone for very long, and we've made sure to give her plenty of attention. But I do think she suffered from some form of post-traumatic stress. Weeks later, she still jumps at sounds as slight as the dropping of a spoon - and, of course, at the sound of gunfire. She no longer cries when we leave, but she won't place a paw outside the front door even if it's wide open - an impulse none of my previous cats could ever resist.

She has also developed a habit of licking my hand after I've pet her. I believe that's probably Lola's way of soothing herself, so I let her do it.