This stage migrates into the mosquito's salivary glands. When the mosquito bites a dog the worms are injected into the dogs skin. The larva remains in the dog's skin and underlying tissue for up to four months and then migrates into the bloodstream. Through the bloodstream the larval heartworms are carried to the heart where they live in the blood within the chambers on the right side of the heart. In the heart and lungs the larval worms mature into adults and may reach twelve inches in length or more.
Many infected dogs exhibit no symptoms until the disease is in an advanced state.
Then one may notice a decrease in activity, often accompanied by a cough. Left untreated, dogs with heartworm will eventually die from failure of the heart. This is an autoimmune disease in which the body attacks its own red blood cells. Antibodies are normally formed by the dog's immune system when needed to destroy invading bacterial or viral signs. However, with AIHA, the dog's immune system see its own red blood cells as foreign, and therefore produces protein molecules to destroy them.