Heartworm illness infects the lungs of dogs, cats, and ferrets, causing severe lung disease, heart failure, organ damage, and death. A parasitic worm, Dirofilaria immitis, is the cause. Mosquito bites spread the worms. The dog is the model host, meaning the worms grow, mate, and reproduce only within the dog. The mosquito serves as an intermediary host, where the worms dwell briefly before becoming infectious (able to cause heartworm disease). Adult worms reside in sick animals’ hearts, lungs, and blood vessels.

What is the heartworm’s life cycle?

The heartworm parasite’s life cycle is complex, requiring an intermediary host in the mosquito before it can infect the dog. Mosquitoes spread heartworm. Up to 30 mosquito species carry heartworms.


A female mosquito consumes microfilariae when she bites an infected dog during a blood meal. Microfilariae develop for ten to thirty days in the intestines of the mosquito before they enter its mouthparts. They are infectious larvae capable of maturing in a dog at this stage. Infectious larvae enter the body when a mosquito bites a dog.

Where can you find heartworm disease?

Heartworm disease in canines is prevalent throughout the world. It was formerly restricted to the United States’ southern and southeast areas. The biggest number of documented cases continues to occur within 150 miles of the Gulf of Mexico and Atlantic Ocean coasts and along the Mississippi River and its tributaries. However, the disease is growing rapidly and has already spread to the United States, including California, Oregon, and Washington.

What is the mode of transmission of heartworm disease?

The disease is not transmitted directly from dog to dog because transmission requires an intermediate host in the mosquito. Thus, disease transmission occurs concurrently with mosquito season, and in many regions of the United States, throughout the year. The number of infected canines and the length of the mosquito season closely correlate with the incidence of heartworm infection in any given area.

What effect do heartworms have on your dog?

Dogs typically do not show clinical signs of sickness for several years. As a result, the illness is most usually found in dogs between two and eight. The disease is uncommon in puppies under one year, as it takes between five and seven months for microfilariae to mature into adult heartworms following infection. Unfortunately, the disease has typically progressed by the time clinical symptoms show. That is why it is important to take your dog to a simi valley animal hospital on a regular basis. 

How is heartworm illness diagnosed?

The majority of the time, simple blood tests can diagnose heartworm infection. Additional testing is frequently necessary to determine the treatment’s safety in heartworm-positive dogs. A few or all of the following tests are recommended before initiating treatment.


Serum antigens of adult heartworms. Blood sampling is required for this test. “Testing for Heartworm Disease in Dogs” contains additional information. Radiology of the chest (X-rays). Radiographs are frequently recommended before initiating treatment for heartworm infection to determine the extent of heart and lung damage.


Prior to initiating heartworm therapy, blood testing may be recommended to screen for heartworm-associated organ damage. Heartworm disease is treated in the same way as other parasitic infections. Visit ParkAnimalHospitalSimi.com to learn more on different veterinarian procedures for your dog.

How is heartworm disease treated?

Melarsomine dihydrochloride is a medicine containing arsenic that the FDA has approved for the treatment of adult heartworms in dogs. It is injected subcutaneously 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 used to eradicate microfilariae from a dog’s bloodstream. To learn more about emergency veterinary problems, click here.

Prevention Is Always Better Than Cure

Numerous heartworm prevention products for dogs are FDA-approved. Veterinary prescriptions are required for all of these drugs. The majority of products are prescribed every month, either as a topical liquid applied directly to the skin or as an oral pill. Oral tablets come in chewable and non-chewable varieties. A single substance is injected beneath the skin every six to twelve months, and a veterinarian can only give the injection.