Canine Heartworm Disease

The dog is considered to be the "definitive host" for heartworms. This means that the heartworm parasite prefers dogs as their favorite species in which to reside. The term "dog" in this instance includes wolves and coyotes as well as our domesticated pets.

Signs of Canine Hearworm Disease

Depending on the number of worms present in the heart and the pet's sensitivity to their presence, the signs of heartworm disease are quite variable. The traditional signs are coughing and "exercise intolerance." These signs often do not occur until later in the course of the disease or go undetected because they occur gradually. Occasionally a patient will react severely to the presence of the parasites and his immune system will produce widespread vasculitis (inflammation of the vascular tissue) resulting in damage to many organ systems.

American Heartworm Society - Hearworm Disease Information

Life Cycle

The parasites are NOT passed directly from one pet to another but must be spread by a mosquito. The adult worms living in the heart will produce baby (immature) worms or larvae called microfilaria. The baby heartworms will circulate throughout the blood vessels but will not develop into adults in this particular animal. These microfilaria must be ingested by a mosquito. As the mosquito feeds on the blood of the infected dog, it will also pick up some of the microfilaria. These microfilaria must undergo further development within the mosquito's mouth parts in order to become infective to another animal. When the infected mosquito bites another dog, the microfilaria will leave the mouth parts, enter the circulation of the bitten animal, proceed to develop into an adult heartworm in the heart and large vessels leading from the heart, and the life cycle will be repeated. It takes about 7 months after exposure before evidence of heartworm infection can be detected. Dogs that have the circulating microfilaria are a source of infection for all other canines that live within range of the mosquito.

Canine Heartworm Disease | Canine Heartworm Lifecycle | Canine Heartworm Treatment
Feline Hearworm Disease | Feline Heartworm Lifecycle
Heartworms in the USA | Preventative Comparisons