by Morgan Medeiros

Created on: February 12, 2009   Last Updated: November 16, 2009

Although canine heartworm is common in dogs throughout the United States, it often goes untreated because of its vague symptoms, with newly infected animals showing no signs of the disease. Heartworms are parasitic worms that live inside the heart and the arteries of the lungs. The worms prevent valves from closing as blood is pumped from one chamber of the heart to the next, which may cause organ failure and eventual death if left untreated. However, once treated, the animal faces a very high chance of recovery.

Especially prevalent amongst the Gulf and Atlantic coasts because of a high mosquito population, heartworms are contracted when a mosquito bites an infected, or "Host" dog. When the mosquito extracts blood from the host dog, it also extracts the larvae of the heartworm flowing through the dog's bloodstream. When the mosquito bites the following, uninfected dog, the larvae are transferred, and the uninfected dog becomes infected. The larvae live in the newly infected animal's skin for several months before becoming large enough to burrow deeper into the tissue and force their entry into the wall of a vein. After entering the vein, the larvae are carried through the dog's blood system to the heart, where they lodge themselves in the right side of the heart, and continue to grow to full size, resembling thin spaghetti, reaching nine to sixteen inches in length. The adult worms remain in the heart, and may also occupy the arteries of the lungs. While in the heart, the worms breed, and produce more larvae that are released into the bloodstream.

Symptoms of a heartworm infection are more acute in an animal that has been infected for a longer period of time, as the number of heartworms accumulates gradually over a matter of months. Recently infected dogs will show no symptoms, while severely suffering dogs will cough, show reluctance in physical activity, be easily fatigued, and have a reduced appetite that results in weight loss. If an animal is believed to be infected, a blood test is performed, checking for larvae in the blood. However, this test will not detect an infection until about seven months after the contracting the disease. An ultrasound can also be performed to check the heart and lungs of the animal for the adult form of the worms.

Luckily, the prognosis for recovery is high if the dog is indeed infected. All but the most severe cases can be treated through a series of injections, with hospitalization recommended but not necessarily required. Physical activity will also be restricted for up to six weeks. Dogs who are the most seriously ill, however, may require surgery.

Preventative medications are available under the distribution and direction of a veterinarian. Preventative medications allow a dog to be bitten by an infected mosquito, with the medication preventing the larvae from maturing, thus avoiding the disease. This can be done by giving oral tablets once daily, with a drug like Pfizer Filaribits, or once monthly, with a drug such as Interceptor or Sentinel. Topical liquids squeezed into a pet's fur, and a vaccination given by a veterinarian is also available.

Heartworm Disease can cause serious health complications, and dogs should be tested if they are suspected to be infected. Preventative measures may save the life of a dog, and should be seriously discussed with veterinarians in order to avoid a harmful infection.

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