US officials are appealing for help as they try to trace the poison believed to have killed hundreds of dogs which died after eating pet jerky from China.
T he Food and Drug Administration says at least 3,600 dogs and 10 cats have become ill since 2007 and 580 dogs have died.
Within hours of eating the suspect jerky, pets lost their appetite, became lethargic, vomited and had diarrhoea and other symptoms. The strips made of chicken, duck, sweet potatoes or dried fruit were sold under a variety of brand names.
There was a decrease in 2007 after some products were voluntarily removed from the market, but the FDA said it didn't want to conduct a recall without a definitive cause.
But in the years since, the FDA has received complaints from pet owners and veterinarians who have seen repeated cases of kidney failure, gastrointestinal bleeding, and a rare kidney disorder.
The FDA's Centre 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.
Testing is complicated because the poison may have come from the manufacturing plant, shipping, transport or anywhere along the way. Scientists have to know what they're looking for to test for it.
The jerky mystery is the worst case of tainted pet food from China since 2007 when there was a nationwide recall of food made by Menu Foods and 1,950 cats and 2,200 dogs died. Kidney failure caused all of those pet deaths and the poison was found to be tainted melamine from plastic packaging in the wheat gluten. About 150 brands of dog and cat food were recalled and included some of the biggest names in pet food.
A federal grand jury indicted two Chinese nationals and the businesses they operate, as well as the US company ChemNutra Inc and its CEO for their roles in importing the poisonous products. A class-action lawsuit awarded more than 12.4 million dollars (£7.7m) in compensation to pet owners whose pets died from the poisoned food.