MANCHESTER, N.H. -- Veterinarians are warning pet owners that some common household foods can be dangerous or even deadly to dogs.

Beth Hardy, of Manchester, is still mourning her parent's dog, Turk. The 5-year-old black Labrador was perfectly fit, but the family didn't know there was danger lurking in the kitchen.

"He smelled food," Hardy said. "He jumped up on the counter and knocked over a bag of raisins onto the floor and started to devour them."

Less than a week later, the dog was dead, a victim of a strange new disorder being discovered in canines. Vets are discovering that grapes and raisins can be poisonous to some dogs. For reasons they still don't know, they create a toxicity in the animal that can cause kidney failure.

"Potentially, dogs who are very small dogs could be having reactions to even four or five grapes," veterinarian Steven Graves said.

Veterinarians say the damaging effects of grapes and raisins are only now being recognized. The symptoms of toxic poisoning include lethargy, vomiting -- usually within an hour of so of consuming grapes or raisins -- and loss of appetite.

Within a few days, the kidneys will have fully absorbed the poisons and begin to shut down. Researchers don't know what it is about the grapes that are hazardous for dogs' health.

"It could be related to the tannins in the grapes or a bacteria or fungus that grows on the grapes," Graves said. "They have seen it in store-bought grapes, as well as grapes that are grown out in the back yard."

Similar studies have found that onions have the same toxic effect on dogs' livers. In rare cases, grapes or raisins caused renal failure in cats and ferrets.

Hardy works for a vet, and she said no one in her office had seen more than one similar case. She and her husband have their own dog, and she said they watch closely what he eats.

"Everybody knows about (the dangers of) chocolate," Hardy said. "Nobody knows about raisins or grapes or onions."

The effect on dogs of a small amount of grapes or raisins over a long period of time is undetermined. But vets are warning pet owners to avoid the fruit completely.