Beware: moldy walnuts are toxic to dogs!

A colleague of mine recently noted that, “It’s moldy walnut season again.” So, I thought moldy walnut toxicity would be a great topic for a post: Why are these walnuts moldy and how does that affect you?

The walnuts of concern are those that fall from trees and remain on the ground during and after wet weather. As they sit there through the cool, wet winter season, a mold forms on them; and although they can turn a furry black color, they often appear completely normal. Once the mold has formed, they are very toxic to dogs, horses, and virtually any other mammal willing to chew on them.

The toxin found in moldy walnuts is called penitrem A. This same toxin forms in the penicillium mold of cheeses, breads, and other human foods. The actual mechanism of action for penitrem A is not fully understood. It appears that it interferes with calcium and potassium channels in smooth muscles and may cause the degeneration in the cerebellum region of the brain. The first would lead to tremors and the second would lead to lack of coordination during movement, particularly walking.

What to look for: The first clinical signs of intoxication by penitrem A are usually panting, restlessness, and drooling. Within a couple of hours, the signs can progress to mild-to-moderate muscle tremors and a stumbling gait. A large amount of ingested mold may cause seizures, increased body temperature, liver damage, and possibly death.

Diagnosis: Whether or not you witnessed your dog eating moldy walnuts, the clinical signs described above are serious and you should seek immediate veterinary attention. Other poisons that can cause a similar presentation include strychnine, metaldehyde (snail bait), organophosphates/carbamates (pesticides and insecticides), methylxanthines (chocolate), and pyrethrins (insecticides), and eclampsia in pregnant animals. Your vet may diagnose moldy walnut toxicity from your dog’s stomach contents or may choose to treat based on clinical signs. The treatment is likely to be the same either way. The real benefit to identifying the specific toxin is that you can begin looking for the source in your environment.

Treatment: Appropriate treatment for these toxicities often begins by inducing vomiting (if signs indicate ingestion was fairly recent) and using activated charcoal to absorb any toxin remaining in the upper GI tract. Your vet will also begin controlling the tremors with valium or a similar medication. In some cases, he may need to use stronger drug like Robaxin (methylcarbamol), a muscle relaxant, to stop the tremors/seizures. Your vet will likely also start IV fluid therapy to counter dehydration, reduce body temperature, and protect your dog’s liver and kidneys from the toxin.

With early intervention and proper treatment, most dogs recover within one to two days.