Heartworm disease in cats is fundamentally different from dogs -- and far more dangerous because there is NO approved treatment. While dogs can be treated with an arsenical drug to kill adult worms, this treatment is lethal to cats. Prevention is literally the only option.
Table of Contents
How Cats Get Heartworm
- Mosquito bites an infected dog or wildlife
- Mosquito picks up heartworm larvae (microfilariae)
- Mosquito bites cat, transmitting larvae
- Larvae migrate through cat's body to the heart and lungs
- Development takes 7-8 months in cats (vs 6 in dogs)
Cat vs Dog Heartworm
| Feature | Cats | Dogs |
|---|---|---|
| Number of worms | 1-3 (often just 1) | Dozens to hundreds |
| Treatment available | NO | Yes (melarsomine) |
| Worm lifespan | 2-3 years | 5-7 years |
| Testing | Unreliable (antigen test often negative with low worm burden) | Reliable antigen test |
| Damage | Severe lung inflammation, sudden death possible from even 1 worm | Progressive heart/lung damage |
Symptoms
- Often no symptoms until crisis
- Coughing (may mimic asthma)
- Difficulty breathing
- Vomiting (not related to eating)
- Weight loss
- Lethargy
- Sudden death: When a worm dies, the inflammatory response can be fatal
Why Indoor Cats Need Prevention
- Mosquitoes enter homes through doors, windows, and screens
- Studies show 25-30% of heartworm-positive cats are indoor-only
- A single mosquito bite can transmit heartworm
- Monthly prevention is inexpensive insurance against a fatal, untreatable disease
Prevention Products
- Revolution Plus: Monthly topical -- also covers fleas, ticks, ear mites, intestinal worms
- Advantage Multi: Monthly topical -- heartworm, fleas, intestinal worms, ear mites
- Heartgard for Cats: Monthly chewable (ivermectin-based)
Frequently Asked Questions
If there is no treatment, what happens to a cat diagnosed with heartworm?
Management is supportive: monitoring, treating symptoms (steroids for lung inflammation, bronchodilators for breathing difficulty), keeping the cat calm and stress-free, and waiting for the worms to die naturally (2-3 years). When worms die, the inflammatory response can be severe and potentially fatal -- steroids and supportive care manage this period. Some cats survive and recover. Others do not. This unpredictability is exactly why prevention is so critical.
