We have always thought the organisms that cause cat-scratch disease, gram negative bacteria of the Bartonella genus, cause disease in people, but not in cats. New research shows this is not always the case. Cases of various disorders in cats and dogs are being traced to infection with Bartonella organisms.

In dogs, many affected pets are also affected with ehrlichiosis or babesiosis, other more commonly diagnosed tick-borne diseases. In cats, there is a correlation between Bartonella and chronic oral disease (gingivitis, ulcers, etc.). Other diseases, specifically feline leukemia virus and feline immunodeficiency virus (AIDS) also cause chronic oral disease. Testing cats for bartonellosis is recommended, as well as testing for these viral diseases if the cats have chronic oral disease. Healthy cats in contact with people with immunosuppressive diseases should also have a blood test for bartonellosis. Cats infected with the bacterium can easily be treated with azithromycin or doxycycline, as well as herbs and supplements.

New research has increased our understanding of the cause of ivermectin toxicity in some dogs. We have known for many years that collies and related herding breeds are more susceptible to toxicity from the same doses of the medication ivermectin when used to treat various disorders (such as mange). The drug, which is normally prevented from entering the nervous system by way of the blood-brain barrier, somehow escapes this barrier and affects the brain.

Now a mutant gene has been shown to be responsible for the toxicity in the herding breeds. The gene code acts to pump medications such as ivermectin out of the brain and back to the bloodstream where they are properly metabolized and excreted from the body. Collies lack the complete gene, thus preventing ivermectin from being removed from the brain.

Two points should be noted: when possible, safer, more natural therapies can be used to treat various problems, reducing the potential for toxicity. Also, the amount of ivermectin in commercial heartworm medications is well below the toxic amount for any canine breed. Collies and herding breeds can be safely given heartworm preventive without concern for toxicity.

— Shawn P. Messonnier is a veterinarian and pet care advocate.