How is Heartworm Disease Treated in Cats?

Reviewed and updated for accuracy on April 29, 2019 by Dr. Hanie Elfenbein, DVM, PhD

It's true—cats become infected with heartworms, too, even though they are more resistant to them than dogs.

Transmitted by the bite of an infected mosquito, heartworm disease can only be prevented with pet prescription heartworm medicine that kill off the immature larvae in the cat’s body before they can become adults.

Therefore, prevention is much easier, safer and cheaper than treating a case of heartworm disease.

If your cat is not protected by monthly preventive heartworm medicine for cats, he/she is at definite risk of being infected with heartworm disease. This potentially fatal disease could result in your cat having adult heartworms living in their lungs and heart, causing many serious problems.

Cats with heartworms will cough, tire easily, have difficulty breathing, vomit and sometimes cough up blood. The symptoms of heartworm in cats vary depending on where the worms lodge in the cat’s body and how many of them are present.

Assessment of Heartworm Disease in Cats

If your cat does contract heartworm disease, your veterinarian will determine the stage of the disease (severity) before suggesting a course of treatment.

There are four stages, or classes of heartworm disease: Class 1 is the least severe and easiest stage to treat. Class 4 is the stage that is the most difficult to deal with, and these animals have the worst chance of recovery.

Cats with Class 4 heartworm disease need some initial care before drugs and treatment are used to stabilize them. This may involve a surgery where the largest worms are physically removed from the heart and largest blood vessels.

Typically, cats are more resistant to developing heartworms than dogs, and in many cases are able to clear a minor infection themselves without treatment. Because their bodies handle the infection differently, there is no approved treatment for heartworm in cats like there is for dogs.

Cats can react very severely to the treatment used for dogs, and it is not recommended except for the most advanced cases where the cat is likely to die without urgent care.

Many veterinarians will choose to treat the symptoms instead of trying to kill off the worms with drugs. Steroid prescription pet medication can be used to reduce some of the reactions associated with infection, and cat antibiotics can weaken the heartworms so that your cat can clear the infection faster.

Your veterinarian will still want to monitor your cat closely for complications.

Heartworm Treatment in Cats

Before prescribing any cat medications, your veterinarian will want to look for any underlying conditions in the cat that may cause problems with recovery.

Chest X-rays will be taken to look for signs of heart disease or lung damage. Blood tests will be run to look for liver or kidney problems that could hamper the cat’s ability to clear the infection from the body. Any such problems discovered will be dealt with first.

If your veterinarian does decide on a course of drugs, your cat must be kept from running or playing, as this may cause a rapid movement of dying or dead worms to the lungs, where they can cause a blockage. The dead worms can also trigger a severe immune reaction similar to anaphylaxis.

During this time you will need to watch your cat closely for signs of coughing, vomiting, depression or diarrhea. Any abnormal signs should be checked by your veterinarian.

Success Rate After Treatment for Heartworms in Cats

There are risks no matter which treatment course you take, whether you allow your cat to clear the infection naturally or use cat heartworm medicine.

Many cats will clear the infection and not require additional treatment, but in some cases, the symptoms may be severe enough to require oxygen therapy and intravenous fluids.

It can take 2-3 years or more for the cat to clear the infection entirely if they survive. Even then, heartworm antigen tests and antibody tests may return false negative and false positive, respectively.

Your veterinarian can check further for the presence of heartworms by taking ultrasound readings of the heart and lungs, and X-rays of the arteries.

To protect your cat against future infections, you will need to keep your cat on heartworm preventive medications for life. It is always safer and less expensive to prevent heartworm infections than to treat them.

By: Jennifer Kvamme, DVM

Featured Image: iStock.com/Stegarau