Heartworm Disease in Cats

Collage of cat images

Content Validated by Dr. Walt Ingwersen, DVM, DVSc, DACVIM (SAIM)

Both cats and dogs are at risk for heartworm disease. Infected cats tend to have fewer heartworms than dogs —typically less than 6—while infected dogs can have up to hundreds. Additionally, infection rates in cats are about 5%-15% of that in unprotected dogs.1 Although it’s less common in cats, as few as one worm can be fatal for cats. Read on to learn more about heartworm disease in cats, and how to help prevent your cat from getting heartworm disease.

Cat sitting by a plant

How Do Cats Get Heartworms?

Cats get heartworms through the bite of an infected mosquito. Because heartworms require 2 host animals to complete their life cycle, the mosquito acts as the intermediate host. Once the mosquito bites an infected animal, it ingests the microfilariae, which develop into infective larvae in the mosquito in about 10-14 days. When an infected mosquito bites a cat, it transfers the infected larvae to the cat, continuing the heartworm larval life cycle and infecting the cat with heartworms.

Signs of Heartworms in Cats

Most heartworms in cats won’t survive to the adult stage of their life cycle. Due to cats’ smaller size, and strong immune response, the presence of even 1 or 2 adult worms can be considered heavily infected. 

Although cats typically have fewer heartworms than dogs, an infection can still be deadly. Heartworms in cats can trigger an intense immune reaction that can cause severe or even fatal symptoms. 

Signs of heartworms in cats include:

  • Coughing, gagging, and rapid breathing (often confused with asthma)
  • Intermittent vomiting of food or blood (in severe cases)
  • Loss of appetite and weight loss
  • Lethargy
  • Rapid heart rate
  • Blindness
  • Collapse
  • Convulsions
  • Sudden death

How Are Heartworms in Cats Diagnosed?

Heartworms in cats can be difficult to diagnose because most cats don’t show signs of infection. If they do show signs, the symptoms can be easy to confuse with other conditions. Typically, your cat will require multiple tests and procedures to confirm a heartworm diagnosis.

These tests include:

  • Several types of blood tests
  • Physical exam
  • X-ray of the lungs and heart
  • Ultrasound of the heart
Cat being pet

How to Treat Heartworms in Cats

There is no treatment to kill adult heartworms in cats. Most cats who are infected will fight off the infection on their own. It’s important to note that since cats are more resistant to heartworms, most cases in cats will resolve within 2-3 years. Unfortunately, the death of worms can cause fatal reactions in cats. If your cat is diagnosed with heartworm disease, your veterinarian will most likely recommend the following depending on their condition.

Monitor for Symptoms

Many cats may be asymptomatic. Therefore, your veterinarian may recommend monitoring for symptoms and supportive therapies as needed.

Supportive Therapies

As symptoms arise, your veterinarian may recommend supportive therapy and monitoring to help manage the symptoms until they pass. Therapies may include corticosteroids, antibiotics, and cardiovascular drugs.

How to Prevent Heartworms in Cats

Heartworm prevention is important, which is why veterinarians recommend starting your cat on prevention at a young age. This is especially true for cats cohabitating with a dog, or any other pet that spends time outside.

Indoor cats who do not interact with outdoor pets are still at risk for heartworm infection, as the mosquito is the intermediate host. All it takes is one infected mosquito to enter the home and bite your cat to transmit the infection.

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