Heartworm Disease in Dogs: What You Must Know

Heartworm disease causes severe lung disease, heart failure, organ damage, and death in dogs, cats, and ferrets. Dirofilaria immitis is a parasitic worm that causes it. Mosquito bites spread the worms. The dog is the definitive host, which implies that the worms grow, mate, and reproduce solely within the dog. The mosquito serves as an intermediate host, where the worms can live for a short time before becoming infective (able to cause heartworm disease). The adults of the worms live in the hearts, lungs, and blood vessels of infected animals.

What is the heartworm’s life cycle?

The heartworm parasite’s life cycle is complicated, requiring the mosquito as an intermediary host before residing in the dog. Mosquitos spread heartworm. Up to 30 different mosquito species can transmit heartworms.


A female mosquito bites an infected dog during a blood meal and consumes microfilariae. Before entering the mosquito’s mouthparts, microfilariae proliferate in its intestines for 10-30 days. They are infective larvae at this stage and can mature in a dog. When a mosquito bites a dog, infective larvae enter the body.

Where can you find heartworm disease?

Heartworm disease in dogs is seen all over the world. It was originally restricted to the southern and southeast regions of the United States. The greatest number of reported cases remains within 150 miles of the Gulf of Mexico and Atlantic Ocean coasts and along the Mississippi River and its tributaries. On the other hand, the disease is spreading and is now present across the majority of the United States, including California, Oregon, and Washington.

What is the mode of transmission of heartworm disease?

Because transmission requires an intermediate host in the mosquito, the disease is not transmitted directly from dog to dog. Thus, disease transmission happens concurrently with mosquito season, which lasts all year in many parts of the United States. The number of infected dogs and the length of the mosquito season are directly proportional to the frequency of heartworm disease in any given area.

What effect do heartworms have on your dog?

Typically, dogs do not show clinical signs of sickness for several years. As a result, the illness is most commonly found in dogs aged two to eight years. The disease is uncommon in puppies under one-year old since it takes 5 to 7 months for microfilariae to mature into adult heartworms after infection. Regrettably, the disease is typically advanced by the time clinical symptoms appear. Check the “visit them hereportion of your vets website to learn more on other treatments for your dogs. 

How is heartworm illness diagnosed?

Simple blood tests can usually detect heartworm illness. Further testing is frequently required to assess the safety of treatment in heartworm-positive dogs. Some or all of the following tests are recommended before beginning treatment.


Serology of adult heartworm antigens. This test requires a blood sample. For more information, see “Testing for Heartworm Disease in Dogs.” X-rays of the lungs (X-rays). Before beginning treatment for heartworm disease, radiographs are frequently recommended to assess the extent of heart and lung damage. Exams (complete blood cell count, serum biochemistry). Blood testing may be recommended before heartworm therapy to assess heartworm-associated organ damage. Click here to learn more about additional veterinary procedures that may be performed on your dog. 

How is heartworm disease treated?

Melarsomine dihydrochloride is an arsenic-containing drug approved by the FDA to treat adult heartworms in dogs. It is injected directly into the back muscles of dogs with stable class 1, 2, or 3 heartworm disease. Advantage Multi for Dogs (imidacloprid and moxidectin) is another FDA-approved drug for removing microfilariae from a dog’s bloodstream. Visit the best emergency vet Simi Valley has available to treat diseases such as heartworm. 

Prevention Is Always Better Than Cure

There are numerous FDA-approved products for heartworm prevention in dogs. All of these medications require a veterinarian’s prescription. The majority of products are administered on a monthly basis, either as a topical liquid applied directly to the skin or as an oral pill. Oral pills are available in both chewable and non-chewable varieties. Every six to twelve months, a single substance is injected under the skin, and only a veterinarian may deliver the injection.