"Whether this particular toxin in this case can create renal failure depends on how this drug works in the body, which may be an entirely different pathway than the anticoagulants," Weinstein said. "Because we aren't yet familiar with this toxin, we can't be confident of the causation link."
Investigators also have not yet determined whether aminopterin is the only contaminant in all the recalled food.
"If it is not the only culprit, as I suspect, the problem isn't over," McGill said, adding that it is also uncertain as to whether the finding will be much help to veterinarians.
According to McGill, even if the aminopterin is the culprit, "most veterinarians have never heard of this product. There will need to be more information put out to suggest therapeutic regimens."
With the widespread notoriety of the deaths associated with the contaminated pet food, some are beginning to speculate whether the result could be greater regulation of pet food safety.
"Certainly, finding something like this would have everyone step back and say, 'How do we make sure this never happens again?'" said Sandy Wellis, communications chair of the American College of Veterinary Internal Medicine.
"Knowing our public, they would probably like more regulation, and it may occur, but it hasn't happened with previous situations like this," McGill said. "There is a call for it, but will the public pay for it because it will make pet food more expensive."