What is Heartworm Disease?

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Fleas and ticks can be harmful to your dog because they transmit disease, but did you know that some species of mosquitoes can cause health problems to our pets, as well? Female mosquitoes feed on the blood from people and other mammals (like our pets).

Geographically, there areas more at risk for different types of diseases. Heartworm disease is spread globally but most frequently exists in coastal regions and areas with warmer climates. Heartworm disease, also known as the “heart parasite” (because adult parasites end up in the heart and main blood vessels) is caused by a parasite called Dirofilaria immitis. When mosquitoes bite our pet, they become at risk of being infected with this gruesome parasite.

Parasite lifecycle

Dogs are infected during the bite of mosquitoes that contain and inject immature forms of the parasite (the microfilariae) into the skin. These are tiny microscopic versions of the parasites that migrate through the subcutaneous tissues and organs of our animals. Once developed, the adult parasites will lodge in the heart, pulmonary artery and lungs. Here, they will reproduce and release new immature forms into the bloodstream.

A mosquito that feeds on the blood of an animal that carries these immature forms becomes infected and will then proceed to transmit the parasite when it feeds an another mammal. Did you know that adult parasites can grow up to 30 cm in length and cause serious damage? Not to mention that human cases of dirofilariasis have also been reported. An infected pet does not mean that their humans are at risk as human infection only occurs from mosquito bites as well. However, the parasite behaves differently in the human body, sometimes not reaching its adult form (forming only cysts) and not being able to reproduce and form the tiny microfilariae that would infect others.

The importance of controlling these agents by protecting our pets is important. If our pets are protected, we reduce the possibility of their becoming infected by parasites or spreading the disease.

What are the signs?

Heartworm disease has a slow progression – it requires about 6 months until the lifecycle of the parasites is complete. As the disease progresses, the animal suffers from cough, respiratory difficulty, weight loss, intolerance to exercise and heart failure, liver and/or kidney disease.

The diagnosis of heartworm disease can be made based on the clinical history and evolution of the symptoms, along with some blood tests that detect the immature forms of parasites in the blood or, more specifically, through the detection of proteins released by the adult parasites.


Though not risk free, heartworm disease can fortunately be treated. In order to achieve a complete cure, adult and immature forms of the parasite must be eliminated. However, there is a danger of embolism (when parasite forms clog a blood vessel). The animal may endure severe shock if the dying parasites release too many foreign substances into the bloodstream at once. Therefore, the treatment requires hospitalization and continuous monitoring.


Taking preventive measures and avoiding the risk of infection is your best course of action. The treatment is so risky, as well as the disease, that making sure your pet doesn’t become infected in the first place is the only responsible thing to do. There are several forms of protecting your pet: preventives (like insect repelling collars and deworming pills), reducing exposure to mosquitoes and periodically testing for heartworm.


You may think that if your pets don’t exhibit any symptoms around mosquito season, they’re fine. The truth is yes, mosquitoes are around in certain times, mostly when temperatures rise. However, the progression of disease is so slow, that it is possible to remain undiagnosed for weeks or months until adult parasites are grown enough to start causing symptoms.

Ask your veterinarian if you live in an endemic region for this disease and what the most appropriate measures are for someone who resides where you reside, follows your disease prevalence and has your pet’s lifestyle. And use the Petable app to add the deworming and prevention events to your pet’s upcoming events so that you never forget another treatment.

Author: Petable Team

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