The Food and Drug Administration is asking pet owners and veterinarians to help solve a mystery: Why have jerky treats coming mostly from China sickened more than 3,600 dogs and cats and killed at least 580 of them since 2007?
The number of illnesses and deaths - the vast majority of which have affected dogs - has risen since January.
"Much like us humans, these pets ought to be able to eat their food and not get sick from it," says Michael Blackwell, president of the Humane Society University.
Blackwell says there is little the consumer can do.
"It you are dealing with a contaminant or an adulterant, it's not going to show up on the label."
The agency is not issuing a recall or naming brands of jerky treats. It says most have been made in China, but notes that manufacturers are not required to list the country of origin for ingredients on pet food labels.
There was no comment on the allegations in Chinese media on Thursday.
Poor food safety remains a major problem in China despite numerous recently publicized crackdowns on factories. Worries about food safety regularly tops surveys here of people's most pressing concerns, as some manufacturers continue to break the law by using fake, low-quality or toxic ingredients to boost profit margins.
The FDA, in partnership with the USDA, makes sure that the food that is fed to animals in America is a safe and high-quality product. However, just as with human food, the FDA handles pet food complaints but doesn't pre-emptively study every product brought into the U.S.
The FDA now needs details on more cases and more blood, tissue and urine samples from affected pets, according to an update posted Tuesday.
The FDA will cover the cost of the tests to get to the bottom of the outbreak. Official Bernadette Dunham called the wave of pet illnesses "one of the most elusive and mysterious outbreaks we've encountered."
The FDA says several jerky pet treats were removed from the market in January after testing found they contained "up to six drugs." The agency says it's unlikely the drugs caused the illnesses, but that the rate of illnesses dropped after that, probably because fewer of the products were available.
The update says consumers should "be cautious about providing jerky treats" to pets. "If you do provide them and your pet becomes sick, stop the treats immediately, consider seeing your veterinarian and save any remaining treats and the packaging for possible testing."
Tina Wismer, medical director of the ASPCA Animal Poison Control Center, says that this outbreak is different than those in the past because of how long it has lasted.
"The fact that this has gone on for an extended period of time is different. In the past, all of the contaminated food has gone out at once, they figure out what it is, and there is a recall," Wismer says. "The earliest cases in this were reported years ago."
What the pets have in common: They became ill, usually within hours, after consuming treats sold as jerky tenders or strips. The treats are made of chicken, duck, sweet potatoes or dried fruit. Typical symptoms include decreased appetite and activity, vomiting, diarrhea, increased water consumption and increased urination. Some affected pets suffer kidney failure.
Dunham directs the FDA's Center for Veterinary Medicine, which says it has already conducted 1,200 tests and visited jerky manufacturers in China.
"Americans value their pets as family members," says KC Theisen, director of pet care issues for the Humane Society of the United States. "An obvious answer is not jumping off the page. The FDA needs more data and more information, so they are turning to the public."
Pet ownership has boomed in the past decade in China, a nation better known worldwide for its citizens' delight in eating all manner of animals. China's economic development has spurred social changes too, such as growing interest in keeping pets for companionship.
The Chinese government has been faced with several scandals involving food for people, but pet food is also a target of illegal and often dangerous product adulteration. Beijing's promises to get tough on law-breakers have long been hampered by a highly fragmented regulatory system.
The FDA opened its first overseas office in China in 2008 in response to increasing food and drug imports into the USA from China. The move followed a series of food safety scares ranging from pet food to powdered milk to candy.
Chinese Internet users often post online their worries about the quality of Chinese pet food. In recent months some have posted details about pet deaths they blame on toxic products.
Many blame the dog food they bought from individual sellers on the highly popular Internet shopping website Taobao. Some owners say they are now preparing their dogs' food by themselves and share online details of ingredients and recipes.
The FDA has released a fact sheet on its site so pet owners can be aware of possible symptoms.
Natalie DiBlasio and Kim Painter, USA TODAY/Contributing: Calum MacLeod in Beijing