Heartworm Update

Even as a veterinarian who knows the risks associated with heartworm, I think it is easy to become complacent. We see so many negative tests that it can come as a shock when one comes back positive. That’s what recently happened in our clinic and it had us all revisiting the subject of heartworm disease and how to prevent it.

Monterey County is an area where 1 out of every 205 dogs test positive for heartworm or, put another way, the average veterinary hospital in Monterey County has 1-5 dog patients with heartworm each year and the incidence is gradually increasing.

There are plenty of articles out there on heartworm disease and I don’t think I need to rehash them, but if you are interested in learning more I would point you towards the Companion Animal Parasite Council website (www.capcvet.org) for basic information or the American Heartworm Society website (www.heartwormsociety.org) for more in depth information.

What I did want to go over were some interesting points about treatment that make it more obvious why we recommend prevention for all dogs and cats so that treatment isn’t even a necessity.

• One of the most important parts of treatment is exercise restriction. This is because as we kill off the heartworms, or even as they die naturally, they drift off in the blood vessels and lodge in the little arteries of the lungs, stopping blood flow to parts of the lungs. With exercise it is thought that bigger chunks of worms will lodge in bigger arteries and make the lung disease that comes secondary to treating heartworm disease that much worse, even fatal. Exercise restriction should begin at diagnosis and continue for up to 2 months after the final treatment resulting in a total of about 5 months of exercise restriction. Can you imagine only taking your dog out on a leash to go to the bathroom, not walk around, and then bring them inside and cage rest them for close to 5 months? If your dog is needing to be cage rested, please see this video of how to keep him/her mentally active during his/her confinement: Crate Rest Activities for Dogs

• Another difficulty with treatment has to do with the expense and supply of the medications used. Melarsomine is the drug used to treat heartworm and it is, and has been for over a year, on manufacturer hold which means they are not making more. There is a small supply available, but as you might expect, this costly drug is now even more expensive due to its scarcity. In addition to Melarsomine, part of the treatment for heartworms is giving an antibiotic, Doxycycline to kill the bacteria that live within the worms. This antibiotic has been back-ordered and, again due to scant supply, is quite expensive and can be difficult to get in stock.

• As if those two issues weren’t enough then we come to cats who are always a little different than dogs. In the first place, the testing that we routinely do for dogs doesn’t really work in cats. This makes diagnosing cats with heartworms more of a challenge, but it doesn’t mean that they don’t get the disease. Even being inside is not protective enough as 25-30% of cats that are diagnosed with heartworms are, according to their owners, indoor-only cats. Cats get more respiratory problems than dogs do with heartworms and sometimes they can have gastrointestinal or even neurologic symptoms. In addition to being harder to diagnose and getting different disease symptoms, there is also no drug for the treatment of heartworms in cats, so in their case we have to put them on a preventative and other supportive care and then either surgically remove the heartworms or wait the 2-4 years for the heartworms to die of natural causes.

I think when one considers the difficulties of treatment in terms of cost, changes in daily routine, and with cats the difficulties of diagnosis as well as treatment, that prevention becomes a much more obvious choice. If you would like to discuss heartworm prevention for your dog or cat or have other questions or concerns about heartworm disease, please call us (831) 346-0600.