By Dial A Vet Veterinary Team
Heartworm is famous as a dog disease, so cat owners sometimes skip prevention. Mosquitoes do not respect that logic. When Dirofilaria immitis larvae enter a cat, many die in the lungs and leave asthma-like damage. A smaller number of adult worms may survive. Either way, the cat can become very unwell, and treatment options are limited compared with dogs. Prevention is the practical strategy.
Key takeaways
- Heartworm is present in Australia. Risk varies by region and mosquito season, but many areas justify year-round prevention.
- Cats often show coughing, rapid breathing or vomiting more than classic "heart failure" signs.
- Diagnosis is harder in cats than dogs. Negative tests do not always rule disease out.
- There is no simple adulticide protocol like the one used in dogs. Supportive care and prevention dominate.
- Related: heartworm prevention for cats, heartworm in dogs.
How cats get heartworm
Infected mosquitoes inject larvae while feeding. In cats, the immune system often kills migrating worms in the pulmonary arteries. That death and inflammation cause Heartworm Associated Respiratory Disease (HARD). Surviving adult worms are usually few. Even one or two adults can matter in a small chest.
Indoor cats are not automatically safe. Mosquitoes enter houses. Balcony and enclosed-yard cats still get bitten.
Signs to watch for
- Cough or intermittent breathing effort
- Rapid or open-mouth breathing (always urgent in cats)
- Intermittent vomiting not explained by hairballs alone
- Lethargy, hiding, reduced appetite
- Collapse or sudden death in rare catastrophic worm death events
- Weight loss over time
Some infected cats look normal until a crisis. That quiet course is why prevention beats waiting for symptoms.
When it is an emergency
Open-mouth breathing, blue-tinged gums, collapse, relentless coughing with distress, or a cat that cannot settle needs emergency care now. Do not put a dyspnoeic cat in the car without stabilising advice if an emergency clinic can guide you first. Keep the carrier dark and quiet.
How vets diagnose heartworm in cats
Vets may use antigen tests, antibody tests, chest X-rays, ultrasound and bloodwork. Antigen tests can miss low worm burdens common in cats. Antibody tests show exposure but not necessarily current adults. Imaging looks for lung and artery changes. Your vet interprets the pattern rather than a single tick-box result.
Treatment overview
Unlike dogs, cats are not routinely given the same arsenic-based adulticide protocols. Management focuses on:
- Stabilising breathing with oxygen and medicines chosen by the vet
- Corticosteroids or other anti-inflammatory strategies when lung disease dominates, if appropriate
- Monitoring and time while worms die naturally in some cases, with careful risk discussion
- Surgical removal in rare referral situations with accessible worms
- Strict future prevention so reinfection does not stack damage
Never give dog heartworm treatment products to cats. Species dosing and safety differ.
Prevention in Australian conditions
Many Australian regions have mosquitoes for much of the year. Coastal and warmer inland areas often need continuous monthly (or vet-recommended schedule) prevention labelled for cats. Product choice (spot-on, oral and others) is a veterinary decision based on weight, age, other parasites and health. Keep invoices and set phone reminders. Gaps of a few months can erase protection.
Living with a coughing cat under investigation
While your vet works through asthma, infection, heartworm and other causes, keep a simple diary of breathing rate at rest. Count breaths for 30 seconds when the cat is asleep and double it. Rising resting rates, especially with open-mouth breathing, mean you should not wait for the next scheduled appointment. Use a calm carrier routine for rechecks so stress does not fake-worsen respiratory effort in the waiting room.
Indoor enrichment still matters during work-ups. Puzzle feeders at floor level beat high climbing if breathing is borderline. Ask before starting steroid trials at home for "asthma" when heartworm has not been considered, because anti-inflammatory plans and diagnostics should be coordinated.
FAQ
Can I test once and skip prevention if negative?
A single negative test is not a lifelong all-clear. Prevention remains the reliable shield.
Is heartworm contagious cat to cat?
No. It requires a mosquito intermediate host.
My cat has asthma. Could it be heartworm?
The two overlap clinically. Tell your vet so both are considered.
Do urban apartments have zero risk?
Risk is lower than swampy acreage, but mosquitoes still bite indoors. Ask your local vet about regional advice.
Talk with a vet
Questions about feline heartworm prevention or a coughing cat? A Dial A Vet veterinarian can review your region and history. Book a Dial A Vet consult.
References
- Merck Veterinary Manual. Heartworm disease in cats.
- American Heartworm Society. Feline heartworm guidelines (comparative clinical reference).
- Australian veterinary parasitology guidance on Dirofilaria immitis prevention.
Disclaimer: Educational only. This page does not replace an examination or advice from your own veterinarian. If you are worried about your pet right now, contact your local vet or nearest emergency animal hospital.