Heartworm Disease in Cats

Heartworm Disease in Cats

Feline heartworm disease is a serious and potentially fatal disease that is becoming more common. Heartworms most commonly affect dogs, but cases involving cats are on the rise. The veterinary community is spending an enormous amount of money to improve the public education level on the disease in hopes of decreasing the high numbers of cases being diagnosed.

Signs & Symptoms of Feline Heartworm Disease

The signs and symptoms of heartworm disease in cats are vaguer than those seen in dogs. The most common signs are:

An acute cough and rapid breathing


Weight loss

Lethargy/Low energy


There have been cases documented where cats have died suddenly due to respiratory failure.

Causes of Feline Heartworm Disease

Heartworms are a species of roundworms that live in the arteries of the lungs and heart, and the blood vessels that surround both. The infected worms are transmitted from mosquito to cat after the mosquito has picked up the parasite from an infected cat. The mosquito is the carrier of the disease and the cat is the host for the disease. The mosquito carries the young immature heartworm, known as microfilaria. This young heartworm matures into the infective stage in the mosquito and then is passed to a cat once the mosquito bites it. The deposited heartworm lands on the skin and begins to migrate through the skin and connective tissue, where it eventually makes it to the cat’s bloodstream. Once in the bloodstream, the worm is transported to the lungs, where it continues maturation and will begin to reproduce offspring. This entire process generally takes six months, while the adult heartworm can live in the cat up to seven years. Cats of any age or breed are susceptible to infection.

As the heartworms multiply and take up space in the pulmonary arteries, a tremendous amount of damage is often the result. These worms will also take up residence in the right side of the heart. Once inside the heart, the flow of blood becomes restricted and this reduces the amount of blood to other organs in the cat’s body. If there are a large number of heartworms residing in the heart, this disrupts the function of the valves, causing heart damage. Congestive heart failure can be a complication with the more severe cases of heartworm disease. While the worms are lodged in the pulmonary arteries, this causes a decrease in blood flow and, most importantly, the amount of oxygen that is getting to vital organs. These are worms that have been measured to be 6 to 20 inches long. Heartworms are NOT contagious from one cat to another by any kind of direct contact.

Diagnosis of Feline Heartworm Disease

Diagnosing heartworms can be done at your veterinarian’s office with a few simple in-house blood and antigen tests. Currently there is a test that requires just a few drops of whole blood from your cat and can be run in about 10 minutes. This test will show a positive if there is enough of the heartworm antigen in the bloodstream. If it is positive, an additional blood test known as a direct test, a sample again of whole blood, is examined under the microscope and the young heartworms can be seen. The number of baby heartworms that are present on the direct test gives an indication of how advanced the disease is. If your veterinarian suspects the positives from the blood tests are correct, he or she will want to do some radiographs and ultrasounds of the heart to determine what condition the organ is in. Once all of this information has been examined, your veterinarian will stage the disease from mild to severe and this will determine what treatment plan will be best.

Treatment for Feline Heartworm Disease

Heartworm disease is generally a very treatable disease in dogs; however this is not the case with cats. Currently there is no drug available that is labeled for the use of heartworm treatment in cats. One of the drugs for treating dogs has been used in cats, but there are potentially significant side effects. Generally, your veterinarian will offer two choices for treatment:

Treat with the drug labeled for dogs, knowing that there is a high risk of complication.

Treat the symptoms of heartworm disease with the hope your cat’s life will be longer than that of the heartworms. Heartworms can live in a cat for two years, so several months of treatment are needed.

Prevention of Feline Heartworm Disease

Heartworm disease is absolutely preventable. There are currently several once-a-month heartworm preventive drugs that are available through your veterinarian. A heartworm prevention plan is essential to a complete wellness plan for your cat.

If your cat has heartworms and is treated successfully, he/she can get the disease again if you do not follow a monthly heartworm preventive program.

Your veterinarian should recommend yearly heartworm testing for your cat.

Your veterinarian should recommend the first heartworm test to be done when your cat is six months old.

Heartworm prevention can be started as early as six weeks of age.

Indoor cats can GET heartworms. It only takes one infected mosquito to come in and bite them