What It Is:
Heartworm disease is a serious and potentially fatal condition caused by the parasite Dirofilaria immitis, which is transmitted through mosquito bites. While heartworm is more common in dogs, cats can also become infected. In cats, the disease presents differently. Even a single worm can cause severe respiratory issues or sudden death.
Because cats are not natural hosts for heartworms, the parasites often do not reach maturity, but they still trigger intense inflammatory responses, especially in the lungs.
🐾 Common Symptoms
Symptoms vary and can be subtle or severe. Many cats show:
- Coughing or wheezing
- Labored or rapid breathing
- Vomiting unrelated to eating
- Lethargy
- Weight loss
- Decreased appetite
- Sudden collapse or sudden death in rare cases
Some cats show no signs at all until the disease is advanced or fatal.
🦠 Causes and Transmission
Heartworm disease is caused by immature worms transmitted by mosquitoes. The worms travel through the bloodstream and typically lodge in the heart, lungs, or nearby blood vessels.
Steps in transmission:
- A mosquito bites an infected animal and picks up immature heartworms
- The mosquito then bites a cat and transfers the larvae
- In cats, the worms may die before reaching adulthood, but they can still cause lung damage and inflammation
Unlike dogs, cats usually have fewer worms, but the immune reaction is more intense and unpredictable.
🔍 Diagnosis
Heartworm disease is very difficult to diagnose in cats. There is no single test that is completely reliable.
Your vet may use a combination of:
- Antigen testing to detect adult female heartworms
- Antibody testing to detect exposure to heartworm larvae
- Chest X rays to identify changes in the lungs or arteries
- Echocardiogram (heart ultrasound) to detect live worms
- Bloodwork to rule out other causes of respiratory symptoms
Many cats are misdiagnosed with asthma or bronchitis due to similar signs.
💊 Treatment
There is no approved drug to kill adult heartworms in cats, unlike in dogs. Treatment focuses on supportive care and managing symptoms.
Options may include:
- Corticosteroids to reduce lung inflammation
- Bronchodilators or oxygen therapy for respiratory distress
- Heartworm prevention medications to stop new infections
- Monitoring with X rays or ultrasounds over time
- Hospitalization during severe flare ups
- In rare cases, surgical removal of worms may be attempted
Because treatment carries risks, prevention is the safest approach.
🩺 Prognosis
Prognosis is unpredictable and depends on the number of worms, the cat’s immune response, and access to care.
- Some cats recover fully with supportive care
- Others may have chronic respiratory disease
- Sudden death can occur from a blocked artery or acute lung reaction
With regular prevention and early care, most cats can avoid the disease entirely.
💡 Cat Owner Note
Heartworm might sound like a dog problem, but it can be just as deadly in cats. The scary part is that many infected cats show no signs until it is too late. A once a month preventive is the best, and only, reliable way to keep your cat safe from this invisible threat.
❓ Frequently Asked Questions About Heartworm Disease in Cats
Can cats get heartworm disease?
Yes. Cats can be infected by heartworms through mosquito bites, even if they live indoors.
How many worms does it take to cause illness in cats?
Even one worm can trigger a severe and life threatening reaction in a cat.
Is there a treatment for heartworm in cats?
There is no approved drug to kill adult heartworms in cats. Treatment focuses on managing symptoms.
Can indoor cats get heartworms?
Yes. Mosquitoes can get indoors, and indoor only cats have been diagnosed with heartworm disease.
How can I protect my cat?
Use a monthly heartworm preventive year round. Your vet can recommend the right product.
Is heartworm testing necessary in cats?
Testing can be helpful if your cat shows respiratory signs, but regular prevention is more important than testing.