Pet jerky treats, mostly imported from China, are now linked to more than 1,000 deaths in dogs, more than 4,800 complaints about animal illness, and, for the first time, sickness in three people who ate the products, federal health officials said Friday.

But, according to JoNel Aleccia of NBC News, U.S. Food and Drug Administration officials say they still can’t identify a specific cause for the reported illnesses or deaths, despite seven years of testing and investigation.

“The agency continues to caution pet owners that jerky treats are not required for a balanced diet and encourage them to consult with their veterinarians, both prior to feeding treats and if they notice symptoms in their pets,” FDA said in a statement.

The humans who consumed the treats included two toddlers who ingested them accidentally and an adult who may have been snacking on the questionable products, which include chicken, duck or sweet potato jerky treats, an FDA official said.

“The agency continues to caution pet owners that jerky treats are not required for a balanced diet and encourage them to consult with their veterinarians.”

One of the children was diagnosed with a salmonella infection, which can be spread by touching contaminated pet food and treats. The other child developed gastrointestinal illness and fever that mirrored the symptoms of dogs in the house that also ate the treats. The adult reported nausea and headache, said Siobhan DeLancey, an FDA spokeswoman.

The agency has received about 1,800 new reports of illnesses and deaths since its last update in October, some involving more than one pet. The numbers now include 5,600 dogs and 24 cats.