Treatment of Heartworms in Cats
By Jennifer Kvamme, DVM
Cats become infected with heartworms, too. It's true. Transmitted by the bite of an infected mosquito, heartworm disease can only be prevented with heartworm medications 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 heartworm preventive medications, 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 his/her lungs and heart, causing many serious problems.
Cats infected with heartworms will cough, tire easily, have difficulty breathing, vomit, and sometimes cough up blood. The symptoms vary depending on where the worms lodge in the cat’s body and how many of them are present.
Assessment of Heartworm Disease
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 One is the least severe and easiest stage to treat. Class Four is the stage that is the most difficult to deal with, and these animals have the worst chance of recovery. Cats with Class Four 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 heartworm drug for cats, as there is for dogs, but in some cases, an adulticide — a drug that kills the adult worms — may be used to lessen the infection. This is not the ideal course of treatment, however, since cats can have a severe reaction to the dying worms. A single worm can break off and lodge in an artery, causing sudden shock and even death if treatment with medication is attempted. In the most severe cases, surgery to remove the worms may be recommended.
Many veterinarians will choose to treat the symptoms instead of trying to kill off the worms with drugs. Anti-inflammatory drugs can be used to reduce some of the reactions associated with infection. Your veterinarian will still want to monitor your cat every six months for complications.
Treatment and After-Care of Heartworm Disease
Before giving any medication, 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 problems discovered will be dealt with.
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 a large number of dying or dead worms to the lungs, where they can cause a blockage. 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 and the Future after Heartworm Disease
There are risks no matter which course you take; whether you allow your cat to clear the infection naturally or use drugs. 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 for the cat to clear the infection entirely, and 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 radiographs of the arteries.
To protect your cat against future infections you will need to keep your cat on heartworm preventive medications for life.