Dogs and Heartworm

Dogs and Heartworm: What You Need to Know to Keep Your Dog Safe

Heartworm disease is a parasitic infection that often leads to heart failure, organ damage, lung disease, and death in dogs. The parasitic worm, ‘Dirofilarial immitis’ is spread via the bite of a mosquito. The dog’s body then acts as a host for the parasite. The parasites are commonly called ‘heartworms’ because the adults live in the heart, blood vessels, and lungs of the canine. 

The Life Cycle of the Heartworm

The offspring, known as microfilariae, reside within the infected dog’s bloodstream. When a mosquito bites a dog with heartworms, the microfilariae infect the mosquito.

Inside the mosquito, the microfilariae live for about 10 to 14 days. The mosquito can then spread the microfilariae to other dogs via the bite. Once the microfilariae infect the dog, it takes about six to seven months for the larvae to fully mature into adult worms. The adult worms’ mate within the dog’s system and the female then releases her microfilariae into the animal’s bloodstream. 

Heartworms are not contagious so your dog cannot catch the parasite from other canines but instead must become infected via a mosquito bite. 

The adult heartworms can easily live five to seven years inside the pet. The adult male works will reach six inches in length and the females up to 12 inches. The number of worms that can reside within a canine is referred to as the ‘worm burden’   A worm burden can consist of 15 to 250 worms. 

How to Check a Dog for Heartworms

Your dog’s veterinarian will perform a blood test to determine if the animal has heartworms. Ideally, all dogs should undergo testing for heartworms at seven months of age before the owner puts the dog on a heartworm preventative. If a dog is infected and you start prevention, the prevention will not cure the infestation. Heartworm preventatives do not effectively kill adult heartworms. In fact, giving a heartworm preventative medication to a dog with heartworms can lead to the animal’s death by triggering a shock reaction within the animal. 

Treatment of Heartworms in Dogs

Treating a dog infected with heartworms is a costly and dangerous endeavor. The medication used to kill the adult heartworms is  toxic and can have a negative impact on your dog’s health and might even lead to dangerous blood clots. The necessary injections are also expensive, require a multitude of visits to the veterinarian, blood work and sometimes hospitalization. 

Prevention of Heartworms in Dogs

Prevention of heartworms is far easier than treatment. Most heartworm preventatives are given month as either a topical or oral tablet. One product does require an injection every six or 12 months. Many of the heartworm preventive measures are effective against a variety of intestinal parasites that the dog can also contract. They are all highly affordable and effective. Ideally, you should make an appointment with your veterinarian to determine the best course of treatment for your canine companion. 

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Good article and advice. Thank you!


In what part of north America do I need to be worried about this? I live in B.C. Thanks

joseph munn

why? Excellent explanation

mel fernald

Excellent explanation.

mary Ellen fernald

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