3, Jun 2022
Heartworm Disease in Dogs: Things You Need to Know

In dogs, cats, and ferrets, heartworm disease causes severe lung disease, heart failure, organ damage, and death. Dirofilaria immitis, a parasitic worm, causes it. Mosquito bites are a vector for the propagation of worms. The dog is the definitive host, which means the worms develop, mate, and reproduce only within the dog. The mosquito is the intermediary host, where the worms dwell briefly before becoming infective (able to cause heartworm disease). Adult worms are found in infected animals’ hearts, lungs, and blood vessels.

What is the heartworm’s life cycle?

The heartworm parasite’s life cycle is complex, needing an intermediary host in the mosquito before infecting the dog. Mosquitoes are the vectors of heartworm. Up to 30 different mosquito species can transmit heartworms.


A female mosquito bites an infected dog during a blood meal and consumes microfilariae. Microfilariae develop for ten to thirty days in the intestines of the mosquito before entering its mouthparts. They are infectious larvae and can mature in a dog at this stage. Infective larvae enter the body when a mosquito bites a dog.

Where can you find heartworm disease?

Heartworm illness in dogs is present globally. It was originally restricted to the United States’ southern and southeast areas. The highest number of documented cases remains within 150 miles of the Gulf of Mexico and Atlantic Ocean coasts and along the Mississippi River and its tributaries. However, the disease is expanding rapidly and is now present throughout the majority of the United States, including California, Oregon, and Washington.

What is the mode of transmission of heartworm disease?

Due to the need for an intermediary host in the mosquito, the disease cannot be transmitted directly from dog to dog. Thus, disease transmission happens concurrently with mosquito season, which lasts all year in many regions of the United States. How many affected dogs and how long the mosquito season lasts affect the incidence of heartworm disease in any given area.

What effect do heartworms have on your dog?

Typically, dogs do not develop clinical signs of sickness until several years have passed. As a result, the disease is most usually diagnosed in dogs between the ages of two and eight years. The disease is uncommon in puppies under the age of one year, as it takes approximately 5 to 7 months for microfilariae to mature into adult heartworms following infection. Regrettably, the disease has typically progressed by the time clinical symptoms show. Which is why it is always essential to take your dog to places like Park Animal Hospital on a regular basis for check ups. 

How is heartworm illness diagnosed?

Generally, simple blood tests can diagnose heartworm infection. Additional testing is frequently required to determine the treatment’s safety in heartworm-positive dogs. One or more of the following tests are recommended before initiating treatment.


Serology of adult heartworm antigens This test requires the collection of a blood sample. For more information, read “Heartworm Disease Testing in Dogs.” x-rays of the chest (X-rays). Radiographs are frequently recommended before initiating treatment for heartworm infection to determine the extent of heart and lung damage. Exams (complete blood cell count, serum biochemistry). Before heartworm therapy, blood testing may be recommended to assess organ damage caused by heartworms. Visit this page to get more info on veterinary procedures that may be performed on your dog.

How is heartworm disease treated?

Melarsomine dihydrochloride is an arsenic-based drug approved by the FDA to treat adult heartworms in dogs. It is thoroughly injected into the back muscles of dogs with stable class 1, 2, or 3 heartworm disease. Another FDA-approved medicine, Advantage Multi for Dogs (imidacloprid and moxidectin), is used to eradicate microfilariae from a dog’s bloodstream. Visit this emergency vet clinic to learn more about emergency treatments. 

Prevention Is Always Better Than Cure

Numerous products for heartworm prevention in dogs are FDA-approved. All of these drugs must be prescribed by a veterinarian. Most products are used every month, either as a topical liquid applied directly to the skin or as an oral pill. Oral pills are available in two formulations: chewable and non-chewable. A single product is injected under the skin every six to twelve months, and a veterinarian can only give the injection.