Heartworm Season Tracker — Belleview Animal Clinic

Consecutive days · lows ≥ 60°F—/14

Source: Open-Meteo · Denver (39.74°N, 104.99°W) · °F

🦟 Heartworm Disease

What every Colorado pet owner should know

How Is It Transmitted?

Heartworms (Dirofilaria immitis) are spread exclusively by mosquitoes. A mosquito bites an infected animal, picks up microscopic heartworm larvae, and transmits them to the next pet it bites. The larvae migrate through the body and develop into adult worms in the heart and lungs.

The 60°F / 14-Day Rule

Heartworm larvae can only develop inside a mosquito when ambient temperatures remain consistently above 57–60°F, especially overnight. It takes approximately 130 Heartworm Development Units (HDUs) for larvae to reach the infective stage — roughly 14 consecutive days of sustained warmth.

This is why heartworm transmission in Denver is seasonal — our cold nights break the cycle for much of the year.

Why Prevention Matters

Treatment for heartworm disease is expensive, painful, and can be life-threatening
Prevention is safe, effective, and far more affordable
Monthly preventives kill larvae before they mature into adult worms
A simple blood test can confirm your pet is heartworm-free

Signs of Heartworm Disease

Persistent cough
Reluctance to exercise or fatigue after moderate activity
Decreased appetite and weight loss
Swollen belly (fluid accumulation)

Early stages may show no symptoms. Annual testing is recommended.

Schedule an Appointment

Book your pet's exam, heartworm test, or wellness visit online. Or call us directly.

Call 303-794-2008