We are independent & ad-supported. We may earn a commission for purchases made through our links.

Advertiser Disclosure

Our website is an independent, advertising-supported platform. We provide our content free of charge to our readers, and to keep it that way, we rely on revenue generated through advertisements and affiliate partnerships. This means that when you click on certain links on our site and make a purchase, we may earn a commission. Learn more.

How We Make Money

We sustain our operations through affiliate commissions and advertising. If you click on an affiliate link and make a purchase, we may receive a commission from the merchant at no additional cost to you. We also display advertisements on our website, which help generate revenue to support our work and keep our content free for readers. Our editorial team operates independently from our advertising and affiliate partnerships to ensure that our content remains unbiased and focused on providing you with the best information and recommendations based on thorough research and honest evaluations. To remain transparent, we’ve provided a list of our current affiliate partners here.

What is Heartworm?

By S. Mithra
Updated Mar 05, 2024
Our promise to you
AllThingsNature is dedicated to creating trustworthy, high-quality content that always prioritizes transparency, integrity, and inclusivity above all else. Our ensure that our content creation and review process includes rigorous fact-checking, evidence-based, and continual updates to ensure accuracy and reliability.

Our Promise to you

Founded in 2002, our company has been a trusted resource for readers seeking informative and engaging content. Our dedication to quality remains unwavering—and will never change. We follow a strict editorial policy, ensuring that our content is authored by highly qualified professionals and edited by subject matter experts. This guarantees that everything we publish is objective, accurate, and trustworthy.

Over the years, we've refined our approach to cover a wide range of topics, providing readers with reliable and practical advice to enhance their knowledge and skills. That's why millions of readers turn to us each year. Join us in celebrating the joy of learning, guided by standards you can trust.

Editorial Standards

At AllThingsNature, we are committed to creating content that you can trust. Our editorial process is designed to ensure that every piece of content we publish is accurate, reliable, and informative.

Our team of experienced writers and editors follows a strict set of guidelines to ensure the highest quality content. We conduct thorough research, fact-check all information, and rely on credible sources to back up our claims. Our content is reviewed by subject matter experts to ensure accuracy and clarity.

We believe in transparency and maintain editorial independence from our advertisers. Our team does not receive direct compensation from advertisers, allowing us to create unbiased content that prioritizes your interests.

Heartworm is a parasite that infects and debilitates some animals, especially pets such as cats and dogs. The worm requires mosquitoes to complete its reproductive cycle, so it is most common in moist, warm areas like the Mississippi River Valley and Gulf of Mexico. Although entirely preventable, veterinarians can only treat it in the early stages, so it leads to many deaths per year.

Heartworm is classified as a parasitic roundworm. The most common species is Dirofilaria immitis. Worms spread their infection to animals, like wolves, coyotes, ferrets, and foxes, through mosquitoes, but not directly from one mammal to another. Like other parasites, they have a multi-stage reproductive cycle of dormancy and activity to improve their chances of survival.

Heartworm starts with tiny, egg-like young that circulate in the bloodstream of an infected animal. These microfilariae make themselves available to mosquitoes. When a mosquito drinks the mammal's blood, it ingests microfilariae, allowing them to develop into mature larvae inside the insect. This takes a few weeks, after which the mosquito inevitably deposits the heartworm larvae back into a mammal through another bite. The larvae grows and matures into a fertile, adult roundworm in the heart and lungs of the infested animal.

Dogs and cats slightly differ in their quality of infection and related symptoms. In dogs, the heartworm is more likely to migrate to the pulmonary vessels and the right chamber of the heart. Here, a worm can grow for many years, winding through the heart and eventually strangling it. In cats, the worms seem to prefer the lungs. After a few months, pets may develop symptoms.

A cat or dog with heartworm will be tired, easily exerted, listless, eventually exhibiting congested breathing, coughing, weight loss, coughing blood, shallow breathing, and the inability to walk long distances. Perhaps after a period of years, an animal can die from congestive heart failure caused by heartworm.

Just like flea infestations, heartworm can be prevented by monthly doses of medicine. These are available at your veterinarian's office in the form of topical gels, pills, or injections. In climates where the incidence of the parasite is higher, most vets recommend yearly tests to make sure your pet is still healthy, even if they are on preventative medication.

Heartworm can be diagnosed by a blood test. Once diagnosed, other methods of assessing how much damage has been caused to the liver, kidney, heart, and lungs are necessary to begin treatment. In the early stages, shots and surgery may rid an animal of a weak infestation. Some animals may be past the point of confidant treatment. Consult with your veterinarian to make sure your cat or dog is adequately protected.

Frequently Asked Questions

What is heartworm and how do animals get it?

Heartworm is a serious parasitic infection caused by Dirofilaria immitis, which is transmitted through the bite of an infected mosquito. When a mosquito bites an infected animal, it picks up microfilariae, which mature into larvae within the mosquito. These larvae are then transmitted to other animals through mosquito bites, where they can grow into adult worms in the host's heart and lungs.

What are the symptoms of heartworm disease in pets?

Symptoms of heartworm disease may not be apparent until the disease is advanced. Early signs can be subtle, but as the condition progresses, pets may exhibit a persistent cough, fatigue after moderate activity, decreased appetite, and weight loss. In severe cases, animals can develop heart failure and the appearance of a swollen belly due to excess fluid.

Can heartworm disease be treated, and how?

Heartworm disease can be treated, particularly when diagnosed early. Treatment usually involves a series of injections with a drug called melarsomine dihydrochloride, which kills adult heartworms. Additional medications may be prescribed to help reduce inflammation and manage symptoms. Treatment can be costly and lengthy, with strict rest required for the animal during the recovery period.

Is heartworm disease contagious between animals or from animals to humans?

Heartworm disease is not directly contagious between animals or from animals to humans. It can only be spread through the bite of an infected mosquito. This means that an infected animal cannot directly transmit the disease to another animal or a human. However, mosquitoes can transmit the disease from an infected animal to other susceptible animals.

How can I prevent my pet from getting heartworm?

Preventing heartworm disease is much easier and safer than treating it. Monthly heartworm preventatives, available in pill, topical, or injectable form, are highly effective when administered properly. Year-round prevention is recommended by the American Heartworm Society, as heartworm-carrying mosquitoes can be active even in cooler months. Regular testing and veterinary guidance are also crucial for prevention.

Are certain animals more at risk for heartworm disease than others?

All dogs and cats are at risk for heartworm disease if exposed to infected mosquitoes, regardless of their age, breed, or living environment. However, animals that live outdoors or in regions with high mosquito populations are at greater risk. Heartworm disease has been reported in all 50 states in the U.S., so preventive measures are important for all pets.

AllThingsNature is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Link to Sources

Discussion Comments

By serres47 — On Mar 01, 2008

My 7yr old German shepherd developed a gradual swelling in the left leg from mid thigh to toes. recently it started oozing clear fluid. I doubt if it's filariasis. Does dirofilariasis present this way with unilateral leg swelling?

AllThingsNature, in your inbox

Our latest articles, guides, and more, delivered daily.

AllThingsNature, in your inbox

Our latest articles, guides, and more, delivered daily.