Feline
Heartworm Disease


What is feline heartworm disease?

Heartworm disease is caused by a roundworm called Dirofilaria immitis. Heartworms are most commonly found in dogs although they can infect a wide variety of mammals including ferrets, sea lions, bears, foxes, wolves, coyotes, and cats. Adult heartworms live in the heart and major arteries of the lungs, where they interfere with the function of the heart and lungs.

How Are Heart Worms Transmitted?

Heartworms can only be transmitted from one animal to another by mosquitoes. Adult worms living in the heart and arteries of the lungs produce microfilariae (small immature heartworms) which are found circulating in the blood of the infected animal, usually a dog.

If a mosquito feeds on an infected dog with microfilariae in the blood, the mosquito will ingest some of these immature heartworms along with the blood meal. Inside the mosquito, the immature heartworms develop to a stage called the infective larval stage. When the mosquito feeds on another dog or a cat, some of these infective larvae will escape from the mosquito during the blood meal. The larvae pass through the animal's skin through the bite wound left by the mosquito. Once the infective larvae have entered an animal, they will begin migrating through the tissues. They eventually make their way to the heart and lungs where they will mature and begin producing microfilariae.

How Does My Cat Get Heartworms?

Although dogs are the most commonly infected mammals, cats can also get heartworms. Current research suggests infected dogs are the source of most infections for other animals. If your cat lives in an area where heartworm infection is seen in dogs, your cat could be bitten by a mosquito that was infected by a dog.

What are the Signs of Heartworm Disease in Cats?

In cats, heartworms live for one to two years and it is uncommon for cats to have more than two or three adult heartworms. Small numbers of heartworms, however, may cause serious disease in cats.

Clinical signs of heartworm disease in cats vary considerably. Some cats do not show any significant clinical signs of may appear normal. Other cats develop chronic (long-lasting) ,disease. Vomiting or respiratory signs (coughing and difficulty in breathing) are commonly seen in chronic cases of heartworm disease in cats. Vomiting tends to be sporadic and may or may not be related to eating. Coughing may be intermittent or occur in severe, sudden attacks that may take place days apart. in some cases, cats may have severe, acute disease with signs of respiratory collapse and, in some cases, sudden death. In acute cases, death may be so rapid that there is insufficient time to make a diagnosis or offer treatment. Cats that die from heartworms can appear clinically normal one hour before death.

Many other diseases can cause similar clinical signs so it is almost impossible to diagnose feline heartworm disease based on clinical signs alone.

How do I Know if My Cat Has Heartworm

If your cat lives in an area where heartworm is seen in dogs or if your cat is showing signs suggestive of heartworm disease, you should take your cat to your veterinarian. Because the clinical signs of heartworm infection in cats are also seen with other diseases, your veterinarian will probably need to perform diagnostic tests in addition to conducting a thorough physical examination. Many diagnostic tests, such as radiography (X-rays), ultrasound of the heart and lungs, and blood tests, including a new test developed specifically for diagnosis of heartworm infection in cats, are helpful in diagnosing the disease. Ask your veterinarian at the time of your pets next annual exam.

My Cat is an Indoor Cat, Can it Be Infected With Heartworms?

Cats that remain indoors are at much lower risk of getting infected than are cats that go outdoors because of the reduced exposure to mosquitoes. Despite this, heartworm infections have been reported in strictly indoor cats; These infections are thought to be caused by infected mosquitos that gained access to the house.

Should I Get My Cat Tested for Heartworm Infection?

If you lives or travels to an area where heartworm is seen in dogs, or if your cat has signs suggestive of feline heartworm disease, you should consult your veterinarian to discuss having your cat tested.

What Can Be Done if My Cat Has Heartworms?

Unfortunately, treatment to remove heartworms from infected cats can be difficult and hazardous to your cat's health. Various medications can, however, be used to help minimize the clinical signs (coughing, vomiting, difficulty in breathing) your cat may be exhibiting. See your veterinarian for advise on management of feline heartworm disease.


Berkshire Veterinary Hospital
730 1/2 Crane Avenue
Pittsfield, MA 01201
(413)499-2820