Heartworm in the Pacific Northwest

Medical Notes from Dr. Lesley Kovar:

Many of you I have known for years, and many are newer faces to me, or we have not yet met. My name is Lesley Kovar, veterinarian and medical director at Bothell Pet Hospital. I just had my 30 year anniversary here! My plan is to post a monthly blog to you all, to keep you informed on various subjects.

Today we are going to focus on heartworm disease. Heartworm is a roundworm that is transmitted through the bite of an infected mosquito. Once the larvae enter the dog, they develop into adults several months later. These mature worms populate the heart and pulmonary arteries and produce microfilaria (baby heartworms), which live in the bloodstream. Then if a mosquito bites this dog, it ingests the microfilaria, and the cycle continues. The disease can cause severe lung and heart disease, and ultimately be fatal if the parasite load is high.

Historically, heartworm disease has not been an issue in our region due to our cooler

climate. However, recent changes in weather patterns and the influx of dogs from endemic areas suggest that our area can support it. There are reported cases of the disease in dogs that have had no travel history outside of Washington State.

So, while the risk here is considerably less than other states, it is important to consider preventative measures. These medications can help protect dogs from infection if they are bitten by an infected mosquito. It is also recommended that dogs undergo an annual heartworm test, even if they are on preventative medications. This ensures early detection and treatment if an infection does occur. There are several effective and safe prescription medications available, but we recommend Simparica Trio. The advantage of this product is that it not only protects against heartworm, but fleas, ticks, and intestinal parasites as well. Your dog should stay on this preventative year-round because of the increase of warmer days throughout the year.

I personally have treated several dogs that tested positive for heartworm in the past year. These all came from South Korea, however, as I work with a rescue that brings over dogs from overseas. I have yet to treat one that has only lived here in Washington with no travel history, but I suspect that will be changing. What I do know is that the treatment protocol is lengthy, risky, and expensive. It necessitates multiple veterinary visits, chest radiographs, painful injections, and even hospitalization. There are multiple complications which could be life-threatening. The advantage then of putting your pets on preventative is to avoid the stress and expense of this treatment.

For those of you who do adopt a pet from a heartworm endemic area (e.g., southern states like Texas- we see so many rescues from there), it is essential to test at least six (6) months after moving here. This is because the tests only detect female adults and microfilaria, and it can take this long for the larvae to develop to these stages.

So, in a nutshell… Experts in the field are stating that there truly is an increased risk of heartworm now in our area. Simparica Trio costs about the same as the Bravecto we have been recommending for fleas together with a monthly heartworm preventative.

Feel free to reach out to us with questions!

(For more on heartworm and its prevalence in our region, please visit the American Heartworm Society.)