Is Canine Cognitive Dysfunction (CCD) Caused by an Infection?

By Jennifer Coates, DVM on Oct. 11, 2011

Owners of older dogs are all too frequently faced with a beloved pet that seems to have issues with memory loss and confusion. Canine Cognitive Dysfunction is often the diagnosis and is characterized by the following symptoms:

Behavioral changes, including alterations in how dogs relate to people and other animals
Anxiety
Panting
A loss of house training
Restlessness and wandering (dogs may get stuck in corners)
Changes in sleep patterns

Cats can also undergo similar changes as they age, but the feline condition hasn’t received as much attention as it has in dogs (isn’t that always the case?).

Canine Cognitive Dysfunction is common enough that I have found I need a quick and easy way to give owners an idea of what they are dealing with — the phrase "doggy Alzheimer’s" is what I (and others) use. These diseases are very similar, not just in their symptomatology but also in their pathology.

For this reason, a new study in the Oct. 4, 2011 online issue of Molecular Psychiatry got my attention. It reports that Alzheimer’s may develop as a result of infection with a prion (an odd type of protein). A University of Texas press release reports:

"Our findings open the possibility that some of the sporadic Alzheimer’s cases may arise from an infectious process, which occurs with other neurological diseases such as mad cow and its human form, Creutzfeldt-Jakob disease," said Claudio Soto, Ph.D., professor of neurology at The University of Texas Medical School at Houston, part of UTHealth.

"The underlying mechanism of Alzheimer’s disease is very similar to the prion diseases. It involves a normal protein that becomes misshapen and is able to spread by transforming good proteins to bad ones. The bad proteins accumulate in the brain, forming plaque deposits that are believed to kill neuron cells in Alzheimer’s.

"We took a normal mouse model that spontaneously does not develop any brain damage and injected a small amount of Alzheimer’s human brain tissue into the animal’s brain," said Soto, who is director of the Mitchell Center. "The mouse developed Alzheimer’s over time and it spread to other portions of the brain. We are currently working on whether disease transmission can happen in real life under more natural routes of exposure."

This begs the question; could the canine and feline forms of "Alzheimer’s" also be caused by infection with prions? I don’t see why not, since prions seem to be able to jump the species barrier with relative ease.

Hopefully, this and continued research will advance our understanding of these terrible diseases, no matter what species is affected, and lead to better treatment options and prevention strategies.