Pet owners, pet food retailers and manufacturers have a mystery to solve. What's killing or sickening some pets, mostly dogs, which have eaten jerky pet treats from China?

The controversy dates back to about 2007, when the U.S. Food and Drug Administration took note of the increasing number of pet illnesses associated with those treats. Since then the FDA has been looking into the matter, and their latest update was issued in May.

As of May 1, the FDA has collected reports that more than 5,600 dogs and 24 cats have suffered "illnesses which may be related to consumption of the jerky treats."

These reports include more than 1,000 pet deaths, and the FDA adds that "most of the reports they received involve jerky products sourced from China."

In Canada, pet food is not regulated, but the Canadian Veterinary Medical Association has tracked 86 cases in Canada since 2011, involving seven deaths, with a possible connection to jerky treats.

Rosie, a Yorkshire terrier, had just turned a year old when her kidneys shut down after eating Vitalife Duck Tenders every day for three weeks. (CBC)

The jerky products — treats, tenders and strips — are made from chicken as well as duck or sweet potato, possibly containing other ingredients. Most jerky treats sold in Canada and the U.S. originate in China.

In 60 per cent of the U.S. reports, the dogs had a gastrointestinal illness, and in 30 per cent of the cases they suffered from kidney or urinary tract problems.

In about half of the 150 recent cases the FDA considers well-documented, the dogs tested positive for a rare kidney disease, Fanconi syndrome or Fanconi-like syndrome.

Illnesses may be linked to jerky treats

While both the FDA and the CVMA have said the illnesses may be linked to jerky treat consumption, the FDA says "we are still not able to identify an exact cause-and-effect nature."

So far the U.S. regulator has been unsuccessful in its efforts to identify a cause for the illnesses and deaths, but is continuing to investigate several sources, including "glycerin as a potential source of the reported illnesses."

Without a definitive link, China-sourced jerky products are still for sale in Canada and the U.S., although some retailers are taking action.

For example, earlier this year Global Pet Foods, which calls itself "the largest Canadian-owned pet specialty retailer," issued a directive to its stores not to sell any pet food products from China or products that may contain ingredients from China.

Company president Jim Walker told CBC News that Global had previously stopped distributing food products sourced from China, even though they had not received any illness-related complaints about those products.

Both the FDA and the CVMA recommend caution by pet owners when it comes to giving their animal jerky treats.

Advice for pet owners

This seal on the Vitalife Duck Tenders package says the contents are 'Quality checked in Canada certified laboratories.' They were made in China. (CBC)

The CVMA's first recommendation is for owners to seek advice from their veterinarian on treats that are safe and healthy to feed their pets, as products can depend on the individual animal.

While Richard Goldstein of the Animal Medical Centre in New York says "don't feed jerky treats," the FDA and CVMA don't go that far.

For pet owners who do feed their animals jerky treats, the FDA and CVMA recommend they watch their pets closely for any of these signs of illness:

Decreased appetite.

Decreased activity.

Vomiting.

Diarrhea (sometimes with blood or mucus).

Increased water consumption and/or increased urination.

"These signs may occur within hours to days of feeding the products," according to the FDA.

If a pet displays any of these symptoms for more than 24 hours, or the symptoms are severe, they say to stop feeding the treats but save the remaining treats and packaging, preferably in a sealable bag, and contact your vet.

Pet owners as well as veterinarians should report any animal illness associated with pet food to the CVMA in Canada (communications@cvma-acmv.org or 1-800-567-2862) and to the FDA in the U.S., through their safety reporting portal.

Also read the information on the packaging very carefully, including the fine print. Packages may contain prominent information to make it appear the product is domestic while the fine print says "Made in China."

CBC's Marketplace had jerky treats tested in labs in Germany and Canada for its report Fighting for Fido. (CBC)

If the package contains language like "formulated in Canada," Global Pet Foods' Walker says that should be a red flag for consumers.

Under the federal government's guidelines for labelling and advertising of pet foods, there's no requirement to state where the product was made.

CBC Marketplace recommends asking the company if you want to know the source of its product. Company location information is mandatory.

Finally, check the ingredients list. Closely follow any feeding guidelines provided for the size of your pet. And track product warnings and advisories on pet foods issued by the CVMA and FDA.