Investigators searching for the cause of hundreds of cases of illness and death in dogs that ate chicken jerky made in China have extended their scrutiny to duck and sweet potato jerkies.

On a webpage featuring questions and answers about its ongoing pet jerky investigation, the U.S. Food and Drug Administration (FDA) states in a recent update that complaints this year have expanded to other jerky pet treats, so its investigation likewise has broadened.

Laura Alvey, a spokeswoman for the FDA’s Center for Veterinary Medicine, elaborated in an interview by email: “We have received very sporadic reports of duck/sweet potato products prior to 2012, but lately we’ve received more. The overwhelming majority still encompass chicken jerky treat products," she added.

Since 2006, the agency has received more than 1,300 reports of dogs becoming ill, sometimes fatally, after eating jerky treats manufactured in China. Whether the treats are the cause of illness is an open question. The FDA has tested implicated products for multiple contaminants and toxicants and inspected manufacturing facilities in China but has been unable to identify a culprit.

Numerous brands have been named in complaints lodged by pet owners and veterinarians. In a sampling of about 270 complaints the FDA recently posted online, more than 20 brands are identified. The most cited is Waggin’ Train, referenced in about 75 complaints. Second is Kingdom Pets with 25 mentions, followed by Milo’s Kitchen, named in 15.

In the same sampling of complaints, duck products are involved in seven cases. Sweet potato or yam treats are cited in five. In three of those five, the sweet potato or yam products also contain chicken.

The posted cases comprise complaints received by the FDA’s Office of Regulatory Affairs district consumer complaint coordinators between Jan. 1, 2007, and July 2, 2012.

Not included are complaints received by the agency through its electronic Safety Reporting Portal (SRP) system. Alvey said those cases, too, will be available online once they are reviewed and redacted to protect the identities of those who submitted them.

The postings are prompted by Freedom of Information (FOI) Act requests made to the agency. “As a standard rule, if the FDA receives three or more FOI requests for the same record, we try to proactive(ly) post those records to our website,” Alvey explained.

The illness best known as being linked with eating suspect pet treats is Fanconi-like syndrome, a condition in which the kidneys fail to properly resorb electrolytes and nutrients in the body, instead shedding them in urine. Clinical signs include excessive drinking and urination, known as polydipsia and polyuria; and glucose in urine, known as glucosuria.

A number of dogs described in the posted complaints were diagnosed with or suspected of having Fanconi-like syndrome, but many had nonspecific signs of illness, such as diarrhea, sometimes accompanied by blood; vomiting; appetite loss; and lethargy.

Large, small, young and old dogs alike have been affected. Some complaints tell of multiple dogs in one household falling ill. Others describe a single dog becoming sick, while other dogs in the household fed the same treats show no signs of poor health.

In two instances, cats were said to develop problems after eating suspect treats.

Complaints received by the FDA regarding treats containing sweet potato or duck are consistent with information posted by veterinarians to message boards of the Veterinary Information Network (VIN), an online community for the profession.

In a message-board discussion that started in January, four veterinarians said they were treating or aware of cases of illness in dogs that had eaten sweet potato treats made in China.

In April, a practitioner in Virginia, Dr. Leslie Jones, posted on VIN about an 11-year-old Yorkshire terrier who had been vomiting daily for a week. The dog had to be hospitalized and was found to have glucosuria. She had eaten duck jerky treats made in China.

“Owner said that she has been thinking back to around Christmas when she originally bought these treats and realized that (the dog) has been ‘off’ since then ... ” Jones noted at the time.

A month later, the owner reported to Jones that her pet seemed to be doing better except for episodes of weakness in which she’d shake, collapse and not eat.

The patient ultimately was found to have a pancreatic tumor, which led to her death by euthanasia, Jones told the VIN News Service.

To clarify, Jones said the duck jerky likely made the terrier sick, but she died as a result of what probably was an unrelated condition.

Jones said she welcomes the FDA expanding its investigation to include duck and sweet potato jerkies, and she wishes that the agency would advise veterinarians directly of such developments.

“I have not received any information about the expansion of the investigation except for some anecdotal talk on Facebook,” she said. “Getting the word out to veterinarians in a more cohesive manner has always been an issue (in my opinion), as often, our clients find out about recalls before we as DVMs do.”

In terms of recalls, the jerky inquiry has resulted in almost none to date. Only one brand, Dingo, has been formally recalled since 2007. In that case, the company, Eight In One, Inc., a division of United Pet Group, Inc., stated that its Dingo Chick’n Jerky Treats for dogs, Dingo Kitty Chicken Jerky and Dingo Ferret Chicken Jerky products were found to be contaminated with Salmonella. However, the broader jerky problem is not believed to be caused by Salmonella; the FDA has tested for that bacterial pathogen, among other potential contaminants.

Given the number of cases of illness associated with China-made jerky, many consumers and veterinarians are dismayed that such products continue to be sold. One online petition calling for a ban on chicken jerky from China has attracted more than 19,000 signatures to date. A number of veterinarians are advising their clients to avoid all pet snacks made in China.

Companies that own the implicated brands point to the FDA testing in maintaining that their products are safe. Nestle Purina Petcare, owner of the Waggin’ Train brand, has a prominent note on its Jerky Tenders product webpage. It reads in part:

“We use only high-quality ingredients in our products, and the production facilities are designed and operated to meet U.S. Department of Agriculture standards. We have a dedicated team of quality control experts in China — particularly in the plants — when Waggin’ Train products are being produced. ... The safety and efficacy of our products is our top priority, and consumers can and should continue to feed Waggin’ Train treats with total confidence.”

Similarly, a statement on the website of Milo’s Kitchen, a brand owned by Del Monte, cites the FDA testing and its own internal testing, “all of which has shown our chicken jerky to be safe for dogs to enjoy.”

Kingdom Pets, a brand of Globalinx Pet LLC, which identifies itself as “one of the largest suppliers of jerky dog treats in the world,” did not respond to requests made by telephone and email for comment.

Information on how to lodge a pet food complaint to the FDA is available online.