Heartworms in dogs occur almost everywhere in the United States, although some regions have a much higher infection rate than others. This easily-prevented disease in dogs can lead to heart failure and potentially death. Learning about the complex lifecycle of the heartworm parasite and signs of the disease are an important part of understanding heartworms in dogs.
Heartworms in Dogs: The Heartworm Lifecycle
Dirofilaria immitis is a large worm that prefers to live not in the heart of a dog, but in the
pulmonary arteries. The pulmonary arteries are large vessels that leave the heart and deliver blood to the lungs where it will be oxygenated. Dogs contract heartworms by being bitten by an infected mosquito. Mosquitoes pick up larval heartworms from infected dogs and carry them to new dogs. These larval heartworms, called microfilaria, are picked up from an infected dog when the mosquito takes a blood meal. Microfilaria then mature within the mosquito until they reach a stage where they can be infective to a new dog. This process can take a few weeks at a minimum, but depends on the environmental temperatures. If the temperature drops below 57 degrees F, the process will cease. This explains why heartworm disease cannot be transmitted during cooler months. When the infected mosquito bites a dog, the infective larva are transmitted to the dog through the bite. The larva then spend several months in the dog’s skin before maturing to a circulating adult worm. Once it is in the dog’s bloodstream, it finds its way to the pulmonary arteries and lives there while being nourished by the surrounding blood.
Heartworms in Dogs: Clinical Signs of Heartworms in Dogs
Once infected with heartworms, dogs can have a variety of signs. In cases low numbers of worms, dogs may not show outward signs; however, the presence of worms in the pulmonary arteries starts a potentially irreversible inflammatory reaction that can cause changes in the blood’s ability to clot. Once there are enough worms living in the pulmonary arteries, dogs can show signs including shortness of breath, exercise intolerance, or cough. Dogs with heavy worm burdens do not have enough blood getting to the lungs, and can develop heart rhythm disturbances and heart failure.
Heartworms in Dogs: What You Can Do For Your Dog
If you live in an area where heartworms in dogs are endemic, or you suspect that your dog has heartworms, see your veterinarian as soon as possible and have your dog tested.
Click here to learn about how your veterinarian will diagnose your dog with heartworm disease.
Click here to learn about treatments for heartworm disease in dogs.