Heartworm Disease

March 10, 2014

By Dr. Abiagil Messina



Heartworms cause serious and sometimes fatal damage to the heart, lungs, and other organs. Common clinical signs include coughing, difficulty breathing, and exercise intolerance. Heartworm disease can easily be prevented with monthly preventative pills. Although it is possible to rid your pet’s heart of adult worms, serious complications can develop during treatment.

What Are Heartworms?

Adult heartworms are spaghetti-shaped parasites that live in the blood vessels of the heart and lungs. Mature female heartworms release offspring, called microfilaria, into the blood stream. Microfilaria are very tiny – small enough for a mosquito to ingest when it takes blood from an animal. Mosquitoes transmit heartworms from animal to animal. Although heartworms can occur in cats, they are much more common in dogs.Microfilaria develop for six months in dogs and eight months in cats before they become adult heartworms, and until this time, they migrate through various body tissues until they reach the heart and lungs.

How Do You Detect Heartworm Disease?

Heartworm infection in apparently healthy animals is usually detected with blood tests that either test for a heartworm substance called an “antigen” or for the microfilaria themselves.   Neither test is consistently positive until about seven months after infection has occurred.  Heartworm infection may also occasionally be detected through ultrasound and/or x-ray images of the heart and lungs, although these tests are usually used as further diagnostics in those animals who are already known to be infected.  When we draw blood from your pet at their yearly physical, we are testing for heartworm antigen.  It is important to test your pet every year, so if they are to become heartworm positive, treatment can be instituted as soon as possible to prevent further damage to the heart and lungs.

Treatment and Home Care

If your dog is diagnosed with heartworm disease, treatment will be necessary to kill the microfilaria and adult worms.  Adult heartworms in dogs are killed using a drug that is injected into the muscle through a series of treatments.  During this phase of therapy, short-term hospitalization of your pet is recommended so they can be closely observed in the time immediately following the injection. Once your pet goes home after a heartworm treatment, you will need to strictly confine it for another month to prevent fragments of the dead adult heartworms from obstructing blood vessels in the lungs. Monitoring your pet for fever, coughing, and lethargy is important after heartworm treatment.  These are most often seen 5 to 10 days after treatment.

Unfortunately, there is no effective treatment for heartworm disease in cats.


Pets can easily be protected from heartworm infection with preventative medications. These medications are ideally given after your animal tests negative for heartworms. Most preventative medications are formulated so that they are given at monthly intervals, and are often times flavored to make their administration quick and easy.  For cats, there is a heartworm preventative available that is topically administered. It is widely recommended that you continue to give your pet their heartworm preventative every month, year round.  As discussed, treatment for heartworm disease in dogs is possible, but it is a complicated and expensive process, taking weeks for infected animals to recover.


If you have any further questions about this topic, or any concerns about your pet, please don’t hesitate to call us at Chase Farm Veterinary Hospital (508) 995-9935. 


Not a client here? That’s ok! We are always happy to add new members to our Chase Farm family.  Please call if you are interested in scheduling an appointment, and we would be happy to accommodate you and your pets’ needs as best we can.  If you would like a complimentary hospital tour before, or at the time of your appointment, one of our friendly receptionists are always happy to show you around.


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