April Primus has nightmares that her pets -- five cats, four dogs, a horse and a pony -- are being killed by lethal injection.

Usually these come during periods of peak stress at her workplace, the Loudoun County Animal Shelter: late spring and early summer, when cat breeding season delivers feral kittens by the boxful and she spends hours euthanizing them and then thinking about their souls.

"I still remember my first episode with a kitten," said Primus, 35, a field technician. "It takes its toll."

Like Primus, many shelter workers adore animals but must bear the emotional brunt of animal overpopulation while putting up with a public that often derides their work and treats animals callously. The job can be so traumatic, shelter directors and psychologists say, that workers are often afflicted with nightmares, depression, suicidal thoughts and fears of going to hell.

"Shelter people are at as high a risk or higher as other first responders, like doctors, because of the fact that they deal with crises constantly, but they get so little respect and acknowledgments from the public," said Carol Brothers, a Crownsville clinical psychologist. She leads "compassion fatigue" workshops at animal shelters and founded the nonprofit Support Services for Animal Care Professionals.

In recent years, such workshops have multiplied as shelter directors pay more attention to the patterns of trauma that researchers have documented, said Randy Lockwood, a vice president and psychologist with the American Society for the Prevention of Cruelty to Animals. The Loudoun shelter held a workshop last month.

Shelter officials say they work hard on limited budgets to find animals homes, and they view euthanasia as a consequence of an animal surplus, not a solution. Most shelter workers who last -- attrition rates are high -- say the joy of caring for animals and placing them in loving homes outweighs the negativity.

But battling animal overpopulation is a Sisyphean quest. The Humane Society of the United States estimates that shelters euthanize 3 million to 4 million animals each year.

Even at places that contribute a fraction to the toll, such as the Loudoun shelter, the work can be heartbreaking, workers say. The shelter euthanized 1,360 dogs and cats in the most recent fiscal year, about 47 percent of all the dogs and cats it took in.

Amy Seymour, 27, a dispatcher and desk clerk at the shelter, said workers learn not to bond with animals that do not stand a chance: the brood of dehydrated and worm-bloated kittens she found deposited at the front gate one morning; the sweet-as-can-be pit bulls, a breed that Loudoun, like many jurisdictions, forbids shelters from making available for adoption.

Smaller shelters such as Loudoun's rarely euthanize for space; many animals killed are ill, feral or deemed too vicious for adoption. Others have been confined so long that they become aggressive or self-destructive. But larger shelters often cannot keep up with the volume. Life-or-death decisions can come down to hue: Too many black dogs can mean some have to go, and workers must make the wrenching choices.

Euthanasia, experts say, is just one stressor. Shelter workers say it can be harder to deal with people who treat animals as disposable, offering a litany of excuses -- about moving or about the cat not matching the carpet -- when surrendering them.

Public scorn compounds the stress. Mary Healey, chief operating officer of the Washington Humane Society, said she has been called "murderer" and "killer" to her face. There is a more searing insult, shelter workers said. "People say, 'I don't know how you can do this. I love animals too much,' " Brothers said. That comment suggests shelter workers don't, she said.

At the compassion fatigue workshops, workers share stories, Brothers said. They are taught to discuss their feelings with co-workers and release stress through relaxation, exercise and humor, she said.

Many workers say the best medicine is focusing on the animals they can help. "My lifespan is probably shortened as a result" of the stress, Healey said. "But . . . if I stop working for animals today, I will feel like I have done more for animals in my career than most people have done in their lives."

Primus said some Loudoun shelter workers will not enter the euthanasia room, even though it looks like any other exam room, with an elevated metal table and a Formica counter.

On a recent afternoon, veterinarian Valerie Campbell prepped inside the room. When she started in animal care three decades ago, she said, unwanted animals were sometimes killed in "decompression chambers," a method now condemned for its cruelty. Lethal injection is humane and best for suffering animals, she said.

"I always tell people: Death is not the worst thing that can happen to an animal," she said.

Soon, technicians brought in a gray-and-white cat that had been mewing in a quarantined cage 10 minutes before. Its sedated body was limp, its pink tongue lolled from its mouth, its emerald eyes unblinking. The cat had feline immunodeficiency virus, or feline AIDS.

Campbell shaved the cat's left front leg and inserted the syringe. The cat's eyes dilated, but it didn't move. Campbell listened for its heartbeat. Finding none, she pushed the cat's tongue in its mouth and its eyelids down.

She placed the carcass in a black plastic garbage bag and handed it to an assistant to place in the shelter's freezer.

Campbell and others charged with putting down animals say they concentrate on making the experience peaceful for the animal. One Loudoun shelter worker has a ritual of telling dogs that they are now free to chase cats in heaven.

Primus said she has her own rule for coping: Once inside the euthanasia room, she does not think of the animal as a pet.

That plan can be foiled, though, if the animal is not on board. "One dog was licking my face as they were using the syringe," said Steve Szot, 56, recalling a time he helped with euthanasia at the Washington Humane Society. "It took me days to get over it."

Szot said he was taken off euthanasia duty after superiors noted that he sometimes cried after the procedure. Szot now works as an evening caretaker at the Washington Animal Rescue League, a limited-admission or "no-kill" shelter, where he walks dogs but rarely deals with the public.

His stress level, he said, has plummeted.

Animal care technician Angela Blackman plays with Bear at the Loudoun County Animal Shelter, which euthanized nearly half of the dogs and cats it took in during the most recent fiscal year.