HEARTWORMS IN DOGS…

Cause of Heartworm Disease

Heartworm disease is caused by a roundworm called Dirofilaria immitis. Adult heartwormsare long and skinny, and can be up to 12 inches long. They live mostly within blood vessels of the lungs and in the heart. Heartworms cause irritation and inflammation in the blood vessels, leading to damage. When there are large numbers of worms, or the worms die, serious complications can develop from blockages in blood vessels.

Heartworm Life Cycle

Adult heartworms reproduce and release their larvae, called microfilaria, into the bloodstream of infected dogs. When mosquitoes feed on a dog (or other animal) with microfilaria in the blood, the mosquitoes ingest the larvae. The larvae undergo changes within the mosquito, after which the infected mosquitoes can transmit the larvae to other dogs. The larvae migrate through the skin and tissues, and undergo further development, ultimately ending up in the blood stream where they grow into adult worms and settle in the blood vessels of the lungs and in the heart, a process that takes about 6 months. These worms can then reproduce, starting the cycle over again.

Risk Factors for Heartworm

Where heartworm is found, all dogs are susceptible to infection. Those that spend a lot oftime outdoors may be at greater risk, but indoor dogs are at risk as well. Small dogs tend to be more severely affected by the worms than larger dogs. Heartworm can only be transmitted where temperatures are warm enough to allow the larvae to complete their developmental stages within mosquitoes. It is found in widely throughout the world, mainly in areas with relatively warm climates. Heartworm has been found in all 50 US states, though spread between dogs has not been documented in Alaska.

Signs and Symptoms of Heartworm Disease in Dogs

The severity of symptoms depends on several factors including the number of wormspresent and how long the infection has been present. In mild cases, symptoms may be absent or take years to develop. Signs of infection can include:

􀁸 Coughing

􀁸 Low tolerance for exercise

􀁸 Labored or rapid breathing

􀁸 Bluish tinge to skin

􀁸 Coughing up blood

􀁸 Nose bleeds

􀁸 Fainting

􀁸 Weight loss

􀁸 Fluid accumulation in abdomen

Diagnosis of Heartworm Disease

Diagnosis is made by a blood test to detect proteins produced by the worms (“antigen”) inyour dog’s blood. The test may be falsely negative early in an infection or if only a small number of worms are present, so repeating the test after six months may be necessary to detect an infection. An older test method involves checking the blood for circulating larvae, but this test is not as accurate. In addition to blood testing, radiographs and ultrasound can be used to assess changes in the heart and lungs associated with heartworm disease.