Heartworm disease is caused by a worm called \”Dirofilaria immitis.\” Heartworms are most commonly found in dogs. However, they can infect a wide variety of mammals, including cats, ferrets, sea lions, bears, foxes, wolves, coyotes, and even people. Adult heartworms generally live in the heart and major arteries of the lungs, although they may be found in other areas of the body.

Heartworms can be transmitted from one animal to another only by mosquitoes. Adult worms produce microfilariae (small, immature heartworms). Microfilariae generally are found in the blood of dogs and rarely in cats. The mosquito ingests heartworm microfilariae when biting an infected host (usually a dog). The microfilariae develop in the mosquito into \”infective larvae\” and are deposited with saliva on the cat’s skin as the mosquito is feeding. The infective larvae pass through the skin and migrate through the body tissues.

Clinical signs of heartworm disease in cats vary. Some cats do not show any significant clinical signs. Vomiting and/or respiratory signs (such as coughing and difficulty breathing) are seen commonly in chronic heartworm disease. Cats may have severe, acute disease with signs of respiratory collapse. They may suddenly die.

If your cat is heartworm positive and develops clinical signs, see your veterinarian immediately.

Indoor cats may have lower risk of becoming infected than outdoor cats due to reduced exposure to mosquitoes. However, heartworm infections have been reported in indoor cats. If a mosquito carrying heartworm infective larvae enters the house, it can bite your cat and the larvae may infect your cat.

Your veterinarian may recommend testing in any of the following situations:

• Prior to prescribing heartworm prevention medication

• Pre-anesthetic or pre-surgical screening
• When your cat has signs suggestive of heartworm disease
• When monitoring a cat with heartworm disease
• During an annual health check