As spring settles in and outdoor activity picks up, there’s another seasonal shift to be aware of: mosquito season—and with it, an increased risk of heartworm disease.

Recent trends show a growing number of heartworm cases in Northern Colorado, including Fort Collins and surrounding areas. This rise in cases highlights a crucial reminder for pet owners: year-round prevention and regular veterinary care are essential to keeping your pet safe.

What is heartworm disease?

Heartworm disease is caused by parasitic worms that live in the heart of infected pets. It is spread through the bite of an infected mosquito and can result in severe lung disease, heart failure, and even death if left untreated.

While dogs are the primary hosts, cats are also at risk—even indoor cats. Because heartworm is harder to detect and treat in cats, prevention is the best (and only) defense.

Why Northern Colorado?

Although heartworm was once considered a disease of the South, climate change, travel, and shifting mosquito habitats have made it a growing concern in Colorado. Local veterinarians, including our team at CSU, are diagnosing more positive cases each year.

How you can protect your pets

  • Get tested annually. Annual heartworm testing ensures early detection and safe continued use of preventive medications.
  • Use monthly prevention year-round. There are safe and effective oral and topical preventives for both dogs and cats. Your veterinarian can help you choose the right one for your pet and lifestyle.
  • Remember your cats. Indoor cats are not immune. Because there is no approved treatment for heartworm in cats, prevention is essential.

Prevention is protection

Preventive medicine is a cornerstone of accessible veterinary care. By keeping pets protected from preventable diseases like heartworm, we can reduce the need for more expensive and intensive treatments down the road.

At CSU’s Primary Pet Care service, we believe every pet deserves access to quality, proactive care. If your pet hasn’t been tested or started on prevention, we encourage you to reach out to your veterinarian.

And stay tuned — our new primary care clinic, opening in 2026, will provide community-centered care right here in Fort Collins, built on values of inclusion, education, and accessible health for all pets and people.

📅 Schedule your pet’s annual exam and heartworm test today.
💊 Ask about monthly prevention options during your visit.
🐾 Let’s keep our pets — and our community — heartworm-free.