Dog owners are hyper aware of the dangers heartworms pose to their pet, but many cat owners forgo heartworm prevention because they mistakenly believe cats aren’t affected. However, these dangerous parasites can cause life-threatening consequences for your cat. Our team at Just Cats Clinic wants to dispel some common misconceptions about heartworm disease in cats, to ensure your cat gets the protection they need.

Misconception: Heartworms don’t affect cats

Fact: Dogs are natural heartworm hosts, meaning the heartworms can mature, mate, and produce offspring while inside the dog’s heart. Cats are considered atypical heartworm hosts, and the parasites rarely grow to the adult stage, typically dying three to four months after infection. However, the immature parasites can significantly damage your cat’s lungs and pulmonary vasculature before and after they die, resulting in severe respiratory disease. This condition, called heartworm associated respiratory disease (HARD), occurs when the migrating larval heartworms reach the cat’s pulmonary arteries, causing a strong immune response. The cat’s immune system breaks the parasites down in an attempt to remove them, causing significant inflammation that leads to serious lung disease. Signs include coughing, increased respiratory effort, and vomiting.

A bacteria called Wolbachia also commonly infects heartworms, and this pathogen enhances the parasite’s ability to induce inflammation. In addition, the parasites do reach adulthood in some cases, and can cause life-threatening consequences, including heart disease and saddle thrombosis, a condition that occurs when turbulent blood flow in the heart causes formation of a clot that lodges at the base of the aorta where the vessel branches to supply the hind limbs. The condition causes acute paralysis or partial paralysis of one or both hind limbs. 

Misconception: My cat seems perfectly healthy, so they cannot be affected

Fact: Cats are great at hiding illness of any kind, because they have retained their ancestors’ need to mask vulnerability, and they frequently will act completely normal until a disease has caused irreparable damage. Initially, subtle signs may include decreased appetite, mild lethargy, and weight loss. Heartworm disease has two phases where signs are likely to be apparent. 

  • Immature worms reach the lung — About 75 to 90 days after infection, the immature worms reach the lungs and pulmonary arteries, resulting in severe inflammation. These inflammatory cells enter the lung, and interfere with your cat’s ability to breathe.
  • Worms die — As the cat’s immune system attempts to remove the dead worms, widespread inflammation occurs. This response can affect other body systems such as the kidneys, gastrointestinal tract, and the nervous system.

Misconception: My cat lives indoors, so is protected from heartworms

Fact: Heartworms are transmitted by infected mosquitoes, and cats who live outdoors are indeed at greater risk for being bitten by a mosquito. However, according to the Mosquito Control Association, mosquitoes are adept at finding their way indoors through screens, open doors or windows, and bathroom exhaust vents. They tend to congregate near doorways, so can gain access at an opportune moment to take a blood meal from your cat. In addition, many indoor cats are allowed outdoors on balconies or protected patios, making them vulnerable to mosquito bites. 

Misconception: My cat is in the clear because their heartworm test was negative

Fact: Heartworm disease in cats is more difficult to diagnose than in dogs. The antigen test, which is the most common heartworm test used in dogs, accurately detects adult female heartworms. Heartworms in cats rarely mature to adulthood, and when they do, the infection is usually limited to a single gender population. This means that antigen testing does not detect the majority of heartworm infections in cats. Antibody tests are more sensitive when testing cats for heartworm disease, because they can detect infection as early as two months after the mosquito bite occurred. However, a negative test doesn’t mean the cat isn’t infected, and a repeat test should be performed in about two to three months. Imaging modalities, such as X-ray and ultrasound, may also be needed to help confirm a heartworm disease diagnosis.

Misconception: Heartworm prevention for my cat is too expensive

Fact: No treatment is currently available for heartworm disease in cats, and treatment is focused on supportive care and close monitoring to manage affected cats. Strict exercise restriction is needed, since physical exertion increases the rate the heartworms cause damage. Corticosteroids can be used to help decrease the inflammation, and antibiotics may be prescribed to address the Wolbachia infection. If your cat is not exhibiting significant clinical signs, their condition will be monitored every few months with chest X-rays. In severe cases, oxygen therapy may be needed, and extracting the worms through a surgical procedure is also an option. However, this procedure is extremely dangerous, and many cats don’t survive. Heartworm prevention is the only way to successfully address heartworm disease in cats, and is much less expensive than the ongoing costs of treatment and monitoring your infected cat.

Heartworm disease is a concerning issue in cats, but you can easily protect your cat by providing year-round heartworm prevention. If you would like your cat tested for heartworms before starting a heartworm preventive, contact our American Animal Hospital Association (AAHA)-accredited team at Just Cats Clinic, so we can ensure they remain parasite free.