For years, Pacific Northwest pet owners got a free pass on heartworm. Our cool, damp climate meant mosquitoes — the sole carriers of heartworm disease — just weren't active enough to spread it. That was the old story.
The new story: climate shifts, pet travel, and urban mosquito populations have changed the game. Snohomish County veterinarians are seeing locally acquired heartworm cases. It's no longer theoretical.
🦟 The Bottom Line
Heartworm is 100% preventable, but once a dog has it, treatment is expensive ($1,500–$3,000), risky, and takes months. Prevention costs about the same as a cup of coffee per week.
What Exactly Is Heartworm?
Heartworm disease is caused by a parasitic worm (Dirofilaria immitis) that lives in the heart and lungs of dogs, cats, and some wild animals. The worms can grow up to 12 inches long. A single infected dog can harbor hundreds of them.
The worms don't spread directly from pet to pet. They need a middleman: a mosquito. Here's the cycle:
- A mosquito bites an infected animal and picks up baby heartworms (called microfilariae).
- Those babies mature inside the mosquito for 10–14 days.
- The mosquito bites your dog and transmits the mature larvae.
- Over 6 months, the larvae grow into adult worms in your dog's heart.
Why the PNW Is No Longer Safe
Three things changed:
1. Warmer, wetter winters
Mosquitoes used to die off in November. Now they're surviving mild winters in sheltered spots — culverts, standing water, even plant pots on covered patios.
2. Pet travel
People move to Arlington from California, Texas, Florida — all high-heartworm regions. Their dogs bring the parasite with them, and local mosquitoes pick it up.
3. Urban mosquito species
Aedes and Culex mosquitoes have expanded into suburban Snohomish County. They breed in tiny pools of water — bird baths, gutters, dog water bowls left outside.
Symptoms You'd Actually Notice
Here's the tough part: early heartworm has no symptoms. By the time a dog is coughing, tired, or losing weight, the worms have already been in the heart for months.
- Early (months 1–6): Nothing visible. Only a blood test catches it.
- Middle: Mild persistent cough, fatigue after normal exercise.
- Advanced: Labored breathing, weight loss, fainting, swollen belly (fluid accumulation).
- Severe: Sudden collapse, possible death.
💡 Why Testing Matters
A simple blood test catches heartworm before symptoms appear — which means cheaper, safer treatment. We recommend testing annually for all dogs on prevention, and before starting prevention for any dog over 7 months old.
The 3-Step Prevention Plan
Step 1: Get a baseline test
If your dog hasn't been tested, start here. A heartworm test is a quick blood draw — we offer it at Arlington Pet Clinic, and right now it's 50% off as part of our spring mosquito-season promotion.
Step 2: Pick a prevention method
Three options, all effective when used correctly:
- Monthly chewable tablet (Heartgard, Interceptor) — most common, easy to remember with a monthly reminder.
- Monthly topical (Revolution) — also covers fleas and some parasites.
- 6-month injection (ProHeart) — single shot twice a year, done at the clinic. Good for pet owners who forget monthly doses.
All three require a vet prescription — heartworm prevention can be dangerous if given to a dog that's already infected.
Step 3: Stay on schedule year-round
Skipping doses during winter used to be fine. Not anymore. Year-round prevention is now the standard recommendation for the PNW.
What About Cats?
Cats can get heartworm too — but it's much less common, and there's no approved treatment. Prevention for indoor-outdoor cats is recommended. Indoor-only cats are low risk, but mosquitoes do get into houses.
Cost Comparison
| Scenario | Annual Cost |
|---|---|
| Monthly prevention + annual test | $120–$180 |
| 6-month injection + annual test | $200–$280 |
| Treatment if infected | $1,500–$3,000+ |
Get the 50% Off Heartworm Test — This Month
Walk in Monday through Friday, 9 AM to 5 PM. No appointment needed.
📞 Call (360) 691-9371FAQ
My dog is indoor-only. Do I really need prevention?
Mosquitoes get inside. Even "indoor" dogs go out to potty. The risk is lower but not zero — and the cost of prevention is so low that most vets still recommend it.
Can I buy heartworm prevention online without a prescription?
No — legitimate heartworm prevention requires a vet prescription in the US. If a site sells it without one, it's either counterfeit or illegal.
What if I forget a dose?
Give it as soon as you remember and get back on schedule. If you've missed multiple doses, contact us — we may want to test before resuming.
Straight talk: we'd rather you come in once a year for a $30 test than once in a lifetime for a $3,000 treatment. And yes, the 50% off promo is real — just mention you read this article.