Heartworm disease is a potentially serious problem in every geographic area in the United States. The disease was initially prevelant in the southern coastal ares of the U.S., but due to the movement of dogs with the human population the disease has spread over most of the country. It is currently present in this area, however, with proper preventative therapy heartworm disease will not be a risk to your dog.

What is Heartworm disease?

Heartworm disease is caused by Dirofilaria immitis, a parasitic worm that lives as an adult in the right side of the dog's heart and large blood vessels leading to the lungs. Heartworms do most of the damage in the adult stage, at which time the full grown male worms measure about six inches in length and the females can reach a length of twelve inches.

How do dogs get heartworms?

Heartworms are transmitted from dog to dog by mosquitoes. There are three stages in the development of heartworms in the dog.


1. The adult female, living in the right side of the heart and/or major vessels to the lungs, produces immature worms called "microfilariae" that circulate in the blood stream. The microscopic microfilariae can live up to 3 years.

2. When a mosquito bites an infected dog, it takes in blood containing microfilariae. The microfilariae mature in the mosquito over a period of two weeks to become infective larvae.

3. The mosquito, carrying infective larvae, deposits them in other dogs during blood meals. Larvae develop over 3-6 months and migrate to the right side of the heart. Within 6 months, the larvae develop into adult heartworms that are responsible for the disease process in the heart and lungs. The adult heartworms can live up to 7 years. The adult produce microfilariae, hence completing the life cycle.

What are the signs of heartworm disease?

Signs of heartworm disease may occur within 6 months of infection or may not appear at all depending on the number of adult worms that are present. In most cases, signs will begin within 1-2 years after infection. Typical signs include coughing, labored breathing, weakness, tiring with exercise. Since the signs vary, the disease may be well advanced before the dog begins to show any problems or signs may be mistaken for another problem.

In advanced stages, the heart and lungs can be severely damaged. Eventually, heart failure can occur and the dog can die from damage caused by heartworms unless appropriate treatment is instituted.

How do you diagnose heartworms?

To identify heartworm infection, a blood sample is taken from your dog. This test detects antigens from female worms and is very sensitive and accurate.

How do you treat heartworms?

The elimination of heartworms from your dog requires that your veterinarian give medication to kill the adult heartworms and microfilariae. Immiticide is the recommended treatment to kill the adult heartworms.

There are two treatment options with Immiticide. Depending on the severity of the disease your veterinarian may recommend the two injection method and three injection method. With the two injection method, an injection of Immiticide is given on 2 consecutive days. The three injection method consists of one injection administered intramuscularly and then the pet returns for 2 more injections given on consecutive days. After either method, the pet will return for an oral Ivermectin treatment one month after the last Immiticide treatment to help kill the microfilariae.

Following treatment with Immiticide, your dog must be rested for a minimum of 6 weeks, during which time the dead adult heartworms will slowly be reabsorbed.

The microfilariae must also be elminated so your dog will not be a source of infection for other dogs. This is easy to do using one of the preventative drugs. Ask your veterinarian which prevention is right for your pet.