Dogs in at least three countries continue to get sick after eating jerky pet treats, but new figures from the U.S. Food and Drug Administration show that the rate of complaints received by the agency slowed during much of last year.

Between May and Sept. 30, the FDA received about 270 reports of pet illnesses associated with jerky treats, according to an update posted today. During the six months before that period, the agency fielded some 1,800 complaints.

The slowdown coincides with a shift by treat marketers to move production out of China, where most pet jerkies had been made.

Whether the move away from China can be credited with the diminishing number of new case reports is unclear. The FDA points out that products made outside of China may yet contain ingredients from China.

“We don’t know why the reports have diminished, but there are many possibilities,” FDA spokeswoman Siobhan DeLancey said by email. “Some companies have reformulated, some outlets have ceased selling certain products, and we’ve also had quite a bit of outreach to pet owners and veterinarians. In any case, we’re pleased with what appears to be a downward trend.”

Altogether, the agency has received about 5,000 reports of pet-jerky-associated illness since 2007. The reports relate illnesses in more than 5,800 dogs, of which more than 1,000 died; 25 cats and three people.

Summarizing the nature of the reported illnesses, the FDA said about 60 percent of the cases involved gastrointestinal/liver disease; 30 percent, kidney and urinary disease; and the remainder, a variety of other clinical signs, including convulsions, tremors, hives and skin irritation.

A small proportion of animals — between 5 percent and 6 percent — had a kidney disorder known as acquired proximal renal tubulopathy, or acquired Fanconi syndrome. Characterized by polydipsia and polyuria (increased thirst and urination); and glucosuria (glucose in the urine) in the absence of hyperglycemia (high blood sugar), acquired Fanconi has become a signature disease associated with consumption of jerky treats.

Exactly what about pet jerky is to blame for the illnesses is an enduring mystery. An investigation has turned up various contaminants but no definitive culprit.

In early 2013, multiple manufacturers of chicken jerky treats for dogs recalled their products after a New York state laboratory discovered that the treats contained residues of illegal antibiotics.

In 2014, the same laboratory and a separate laboratory in California found an antiviral drug in jerky treats. Investigators don’t believe the drug residues are the cause of illnesses. Nevertheless, the FDA issued an import alert today directing its field investigators to detain shipments of products that tested positive. “These products cannot enter the country unless the manufacturer or shipper can provide third-party documentation that the products don’t contain illegal antiviral and/or antibiotic residues,” the agency stated.

The jerky problem is international in scope. The Canadian Veterinary Medical Association began hearing of cases in Canada in 2011 and continues to receive periodic reports, association spokeswoman Kristin McEvoy said.

“To date, over 90 cases, including seven deaths, that are suspected to be connected to consumption of jerky treats have been reported to us by Canadian veterinarians and pet owners in eight provinces,” McEvoy said by email.

Australia has been wrestling with the mystery for as long as the United States. A study published in September 2013 by veterinary researchers there documents the problem since it surfaced in 2007 and concludes that unidentified toxicants in implicated pet treats and pet foods are the likely cause.

Dr. Sue Foster, a study co-author who works as a small animal medical consultant to the Australian diagnostic laboratory Vetnostics, told the VIN News Service that the problem has not abated.

“We are seeing cases on at least a monthly basis,” Foster said by email last week. “I think we only see the thin edge of the wedge as I probably hound about five to six vets to get one vet who will actually follow up on my concerns. And these cases are only ones that I pick up through a commercial laboratory (so there will be many more out there).”

Lack of consistent follow-through by practitioners impedes the investigation, Foster said, especially given the complexity of the mystery. “… a wide range of treats seem to cause (illness), and we need more numbers logged to get good epidemiologic data,” she explained. “We also need more vets to test urine as a routine part of a diagnostic investigation when polydipsia/polyuria or an unidentified illness occur in dogs.”

As well, a sole focus on jerky treats as suspects can confound a diagnosis. Foster related a case in which she served as a consultant, involving a 5-year-old shih tzu-Maltese mix, Bambi, who presented with increasing lethargy, loss of appetite, diarrhea and increased thirst. The dog also had episodes of shaking and “would appear to ‘fall asleep while standing,’ ” Foster wrote in a case report published in Australian Control and Therapy, a non-peer-reviewed practitioner forum.

Bambi had eaten a jerky treat made in Thailand, along with two types of semi-moist dog-food rolls, pet mince from a local butcher and chicken breast fillet cooked and mixed with vegetables.

Tests showed the dog had persistent glucosuria. That, along with a normal blood glucose concentration and history of treat ingestion, pointed to a diagnosis of acquired proximal renal tubulopathy. “Neurologic signs didn’t really fit, but the dog seemed to be responding to IV fluids so I ignored them (bad mistake … !),” Foster wrote.

Three days after being hospitalized, Bambi’s neurologic signs worsened to the point that she couldn’t stand.

Consulted again by telephone, Foster said, “Finally, I thought about the neuro signs and the diet, processed dog roll and pet mince both previously having been reported to result in thiamine deficiency in Australia due to added sulphites as preservatives.”

Bambi’s veterinarian, Dr. Joe Katsikaros, could not immediately obtain thiamine, so she gave Bambi a large-dose injection of B complex, which includes thiamine, and followed up with oral thiamine supplements. Within four days, Bambi improved to nearly normal and was able to go home to her “delighted owners,” Foster said.

Manufacturers of the commercial dog roll Bambi had eaten reportedly told the veterinarians that the food contained no sulphites. Katsikaros then paid to have the products and butcher’s pet mince tested. Result: “The culprit for the added sulphite was the mince from the butcher!” Foster wrote.

Foster draws two lessons from the experience: One, analyze the diet carefully, bearing in mind that there may be more than one source of trouble. Two, don’t dismiss signs that don’t fit the picture.

In the United States, the FDA said it will continue to investigate, regardless of the decrease in illness reports. “We are determined to find an answer to the mystery,” the agency said.