🩺 Vet 2025 Guide: Heartworm Infection in Cats – Symptoms, Risks & Prevention 🐱❤️🦟

Most cat owners are familiar with heartworm disease in dogs, but few realize that cats are also at risk—and the disease presents very differently. In this comprehensive 2025 veterinary guide, Dr Duncan Houston explains the symptoms, diagnostic challenges, treatment approaches, and crucial prevention tips for heartworm infection in cats. 🐾

💡 Do Cats Get Heartworm?

Yes! While heartworms are more commonly associated with dogs, cats can and do get heartworm. However, feline heartworm is primarily a lung disease, not a heart disease. This is because cats are not natural hosts for the parasite, which results in severe inflammatory reactions in their lungs—even when only a few worms are present.

🧬 Heartworm Lifecycle in Cats

The life cycle begins with a mosquito bite:

• 🦟 A mosquito feeds on a heartworm-infected dog and picks up microfilariae (baby worms).
• 🧪 These develop in the mosquito and are transmitted to the cat during another bite.
• 🧬 The larvae struggle to develop in the cat’s body, and most are destroyed by the cat’s immune system.

💔 When worms do survive to adulthood, they often die prematurely, triggering intense lung inflammation. Even a single worm can cause serious disease—or death—in a cat.

📊 How Common Is Feline Heartworm?

• 🧾 About 10–20% of infected cats show no symptoms at all.
• 🏠 25–30% of infected cats are considered indoor-only pets.
• 🧩 This means feline heartworm is likely underdiagnosed and more common than expected.

🚨 Symptoms of Heartworm in Cats

Feline heartworm often mimics asthma or other lung diseases:

• 😾 Coughing or wheezing
• 🤢 Vomiting (common but not well understood)
• 😿 Difficulty breathing
• 🧠 Neurological signs (in rare cases)
• 💀 Sudden death in up to 20% of infected cats

These symptoms often appear during the immature larval stage (within 75–90 days of infection) or after the sudden death of an adult worm.

🌬️ What is HARD (Heartworm-Associated Respiratory Disease)?

HARD refers to lung disease caused by larval heartworms in cats:

• 🐛 Larvae reach the lungs and are destroyed by the immune system
• 🔥 Inflammation causes severe damage to delicate lung tissues
• 😮‍💨 Symptoms are identical to feline asthma

🎯 HARD is often the first and only sign of infection. Testing is needed to differentiate it from other respiratory issues.

🔬 Diagnostic Challenges

Diagnosing feline heartworm is tricky:

• 🧪 Antigen Tests: May miss infection, especially if only male worms are present
• 🧫 Microfilaria Tests: Useless—microfilariae are rarely found in cats
• 🧬 Antibody Tests: Helpful but can’t distinguish past vs current infection

🩻 Chest radiographs and echocardiograms are often needed. Testing is typically reserved for symptomatic cats—not as a routine annual screen like in dogs.

💊 Treatment Options

There is no safe adulticide for cats like there is for dogs. Treatment is mostly supportive and includes:

• 🧘 Prednisolone: Reduces inflammation and immune response
• 🦠 Doxycycline: Treats Wolbachia bacteria that live inside heartworms
• 🛌 Monitoring: Chest X-rays every 6 months to evaluate disease progression

If a cat is not sick, the recommendation is to wait out the worm’s 2–3 year lifespan while monitoring lung health. 🐱

⚠️ Risks of Adulticide Therapy

Using dog-style adulticide drugs in cats is very dangerous. One-third of cats treated this way experience fatal embolic reactions. Because of this, adulticide therapy is considered a last resort and only used when absolutely necessary.

🛡️ Prevention is Essential!

💉 The best way to protect your cat is to prevent infection altogether. Monthly heartworm prevention is safe, effective, and strongly recommended—even for indoor cats. 🦟

🚫 Why Indoor Cats Still Need Protection:

• 🏠 25–30% of infected cats were indoor-only
• 🦟 Mosquitoes enter homes easily and are active year-round in many areas

🧴 Heartworm Preventive Options:

• Heartgard® (Ivermectin): Oral monthly chewable
• Interceptor® (Milbemycin): Oral; also protects against roundworms & hookworms
• Revolution® / Revolution Plus® (Selamectin): Topical; covers fleas, mites, worms & heartworm
• Advantage Multi® (Moxidectin + Imidacloprid): Topical; protects against multiple parasites
• Bravecto Plus®: Topical; adds tick control

📆 Year-Round Protection Recommended

🧪 Use monthly prevention year-round in all heartworm-endemic regions. Talk to your vet about which product is best for your cat’s lifestyle and risk factors. 🐾

📱 Need Help Choosing Prevention?

Confused about which product is best for your cat? Visit AskAVet.com or download the Ask A Vet app to speak directly with a veterinary expert like Dr Duncan Houston. We’ll help you navigate prevention, diagnosis, and care—so your kitty stays safe and healthy all year. 🐱🩺

🌟 Heartworm is preventable. Don’t wait—protect your cat today! 🌟