For many years, Washington State was considered a low-risk area for heartworm disease. However, recent trends are changing that. Veterinarians across the state have seen a steady rise in heartworm cases in dogs — a concerning shift linked to warmer weather, increased travel, and the movement of rescue pets from other regions.
Why Heartworm Is Increasing in Washington
Several factors are contributing to the growing number of heartworm cases in the Pacific Northwest:
1. Climate Change
Warmer temperatures are allowing mosquito populations to flourish and expand their seasonal range. Since mosquitoes are the primary carriers of heartworm larvae, more mosquitoes mean a greater risk of transmission to dogs.
2. Pet Travel
With more families traveling with their pets, exposure to heartworm in areas where it’s more common — such as the southern United States — is increasing. When infected pets return to Washington, they can bring the parasite back with them.
3. Rescue Animal Relocation
Many shelters and rescue organizations transport animals from high-prevalence areas in the South to Washington for adoption. While this saves lives, it can also introduce heartworm into local communities if the animals are not properly screened or treated before transport.
4. Migration Patterns
There’s growing evidence linking heartworm spread to seasonal workers and travelers moving between heartworm-prevalent regions and warmer parts of Washington, including the Tri-Cities and Yakima Valley. Pets moving with their owners can inadvertently bring the disease into new areas.
What Dog Owners in Washington Should Do
Even though Washington is still considered a lower-prevalence state, it’s important for dog owners to stay proactive about heartworm prevention.
Talk to Your Veterinarian
Discuss your dog’s specific risk factors with your vet. They can recommend an appropriate prevention and testing plan based on your pet’s lifestyle and exposure.
Consider Year-Round Prevention
While some areas used to recommend seasonal prevention, many experts now advise keeping dogs on heartworm preventives all year long. As climate patterns shift, mosquitoes are becoming active earlier in the spring and lingering later into the fall — making year-round protection the safer choice.
Get Your Dog Tested
A simple blood test can detect heartworm infection. All dogs should be tested before starting prevention, as giving preventives to an already infected dog can cause complications.
Know the Symptoms
Early detection is key. Watch for signs such as persistent coughing, fatigue, weight loss, or diarrhea. Contact your veterinarian immediately if you notice any of these symptoms.
Protecting Washington’s Pets Together
Heartworm disease is preventable — but once it develops, it can be costly and dangerous to treat. As heartworm cases continue to rise in Washington, prevention and vigilance are more important than ever.
Talk to your veterinarian today about the best way to protect your dog and help keep our state’s pets safe from this growing threat.