BY DR. MICHAEL J. WATTS
MY friend’s dog was taking the same type of heartworm medicine that I give my dog. Her dog died last week at the emergency clinic from an illness called IMHA. The ER doctor told her it could be related to the heartworm medication she had been given two days prior or the Lyme disease vaccine given a week earlier. Should I change my type of heartworm medicine?
Please do not switch heartworm medications, or even worse, stop giving heartworm preventive medications, because of this story. IMHA, or immune-mediated hemolytic anemia, is an immune system malfunction where the body attacks and destroys its own red blood cells.
We don’t understand the immune system well enough to know for sure why it sometimes malfunctions. We know that there is a genetic component to IMHA disease. Certain breeds and bloodlines may carry the gene. This is the only certain cause in all cases. But we also know that in sensitive animals any stimulation of the immune system can trigger an attack.
The immune system is stimulated by thousands of different challenges every day. Bacteria in the mouth or skin stimulate the immune system. Viruses and pollens in the air stimulate it. Chemicals and detergents in the environment cause immune stimulation. Insect bites and protein in food can trigger an immune reaction.
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Vaccines are designed to stimulate an immune reaction, so they can indeed trigger an attack in patients with IMHA. Any drug has the potential to stimulate the immune system if an animal is sensitive to it. When a patient with IMHA has a seizure event, it’s usually impossible to tell exactly what triggered it, unless it’s associated with a known vaccine or insect bite.
Although details will have to wait for a future column, I am also a firm believer in Lyme disease vaccination for almost all dogs. I recommend newer recombinant-DNA vaccines which are very gentle on the immune system over older “whole cell” products which are more likely to cause a negative reaction.
A pet with a history or family history of IALA should probably limit vaccines as much as possible. Discuss with your veterinarian which program is most appropriate for your pet.
Heartworm medications are often blamed for IMHA reactions by pet owners, but there is no scientific evidence that the preventatives currently on the market boost the immune system more than other medications. and chemicals to which pets are exposed. It turns out that about one in five dogs with an attack of IMHA have had heartworm preventative treatment in the past week.
Many people take the easy answer and suggest it’s proof of a link. But correlation does not mean causation. The same percentage of dogs who get hit by cars also took a heartworm pill in the past week. Why? Because most dogs get these pills once a month, not because the pills cause car accidents!
The main point here is that unless your pet is directly related to your friend’s, you shouldn’t alter your pet’s diet based on their unfortunate situation. The risk of heartworm disease is very high in Virginia. Four to six thousand dogs are diagnosed with the disease each year in our state.
Preventatives also reduce the incidence of intestinal parasites, which infect up to one in three dogs and pose a very real risk to human health. Almost all Virginia dogs should be given a monthly dose.
We are also seeing more and more Lyme disease every year. I see dogs getting sick and even dying from Lyme disease much, much more often than I see IMHA.
Dr. Michael J. Watts is the owner of Clevengers Corner Veterinary Care in Amissville.