WASHINGTON — The Food and Drug Administration is trying to solve a stubborn mystery surrounding the deaths of almost 600 dogs that ate jerky treats, and officials are hoping pet owners and veterinarians can help them figure out what exactly may be causing the illnesses.

The problem appears to be tied to dog pet treats made in China, the FDA said, though investigators haven't yet found a certain cause. The FDA says it has received reports of illnesses in 3,600 dogs and 10 cats in the United States since 2007, and 580 dogs died. The pet treats were sold under a wide variety of brand names. 

The complaints were sent in by pet owners, some of them unsure of the cause of their pet's illness. But many others were sent in by veterinarians who have seen repeated cases of kidney failure, gastrointestinal bleeding, and a rare kidney disorder, the FDA said.

FDA veterinarian Martine Hartogensis says the agency is now appealing to pet owners and veterinarians to send them more information on animals who may have gotten sick after eating the treats. Pets can suffer from a decreased appetite, decreased activity, vomiting and diarrhea among other symptoms within hours of eating treats sold as jerky tenders or strips made of chicken, duck, sweet potatoes or dried fruit.

“This has been one of the most mysterious and elusive issues we've had to investigate,” Hartogensis said. She said the investigation has been particularly complicated because researchers haven't been able to pin down what ingredient may be causing the problem and because many of the treats and their ingredients are imported. And not much is known about animal deaths. While autopsies on humans can often determine the cause of death, pet owners usually forgo expensive autopsies on their deceased animals.

Dr. Richard Goldstein of the Animal Medical Center in New York said he has been investigating the illnesses since they appeared to begin in 2007, and he is still treating dogs that seem to suffer from the mysterious condition. He was consulted on a case just last week, he said.

In his experience, many of the cases have been small dogs who are eating a large amount of treats. He said the illnesses are rare, so he usually knows immediately when a sickness is connected to the jerky.

He said most dogs he treated were fine if they stop eating the treats. That's why it's important for dog owners to know about the problem, he said.

“The word is not out,” he said. “Some vets don't even know about this.”

The FDA's Center for Veterinary Medicine has run more than 1,200 tests, visited pet treat manufacturing plants in China and worked with researchers, state labs and foreign governments but hasn't determined the exact cause of the illness.

The FDA has issued previous warnings, and a number of jerky pet treat products were removed from the market in January after a New York state lab reported finding evidence of up to six drugs in certain jerky pet treats made in China. The products removed from the market then included Milo's Kitchen Chicken Jerky Treats and Chicken Grillers, made by Del Monte, and Waggin' Train and Canyon Creek Ranch dog treats, made by Nestle Purina.

But others remain on store shelves, and FDA doesn't want to conduct a recall without a definitive cause.

The agency said that while the levels of the drugs were very low and it was unlikely that they caused the illnesses, there was a decrease in reports of jerky-suspected illnesses after some products were voluntarily removed from the market. FDA believes that the number of reports may have declined simply because fewer jerky treats were available.

In complaints posted by the FDA online, many dog owners and veterinarians seem stumped, as well.

In one comment sent to the agency this year, a dog owner whose name was withheld by the FDA wrote that their pet started vomiting and became lethargic and thirsty after eating a chicken jerky treat. The next morning the dog couldn't walk and the owner was told by a vet that there was total renal failure. The dog died that night.

“They said there were many dogs who had died from eating these treats and my vet had treated many sick animals,” the dog owner wrote in documents released by the FDA. “They posted warnings about these treats all over their office and exam rooms.”

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