What is heartworm?

Heartworm is a common disease in dogs and cats which can be deadly if left untreated.  Heartworm disease (dirofilariasis) is caused by a parasite (Dirofilaria immitis). It is transmitted through blood from an infected mosquito.  The mosquito injects the parasite larvae into the animal where it travels via the bloodstream to the heart.

Over time the larvae mature and reproduce, causing the worms to obstruct blood flow to the heart and causes damage to the lungs, heart and arteries.  If untreated, the disease will result in health complications and eventually the death of the animal. Heartworm affects the animal’s health and quality of life long after the heartworms are gone.  This parasitic infection is easy to prevent, but difficult and costly to cure.

How to Test, Treat and Prevent Heartworms?


Regular visit with a veterinarian is important as your pet has to be tested for the presence of  heartworm.  It can take up to six months after infection for a blood test to reveal a positive heartworm infection. A chest x-ray may also be used for diagnosis but this will only be helpful once the parasites have matured and can be seen on an x-ray. It takes the larvae about 7 months to mature into adult heartworm from the time of infection. If the first test is negative, you need to repeat the test six months later.


If a pet tests positive for heartworm infection then treatment needs to be commenced as soon as possible. A drug known as melarsomine is used to eradicate the parasite. However, it is difficult to treat and prevention is a better option. Any larvae which are still circulating need to be eradicated and this treatment and management needs to be supervised by a veterinarian. Treating heartworm infection without professional assistance can delay eradication and complicate the case.


There is preventative medication available for heartworm. However, it is not needed for every pet. Certain regions have a higher incidence of heartworm infection. Pets in these areas may need to use these preventative drugs. Even if a pet has been successfully treated for heartworm infection. preventative medication should still be administered to prevent a new infection.