Canine Heartworm Disease
Heartworm disease is a serious problem affecting dogs in almost every area of the United States. The disease was initially prevalent in the southern coastal area of the U.S.; however, due to the movement of dogs with the human population, the disease has spread readily over most of the country. It is currently present in this area, and cases are reported year-round. Heartworm disease is a condition in dogs caused by Dirofilaria immitis, a parasitic worm that lives as an adult in the right side of the heart and large blood vessels in the lungs. The heartworm does all of its damage in the adult stage, at which time the full-grown male worms measure about 6 inches and the females reach a length of 12 inches. Heartworm disease is much more common in dogs, but also affects cats.
Heartworms are transmitted to the dog by mosquitoes. There are three stages in the development of heartworms in the dog:
- The adult female, living in the right side of the heart, lays immature worms, called microfilariae, in the blood stream. These microfilariae do not grow into adult worms but can persist for up to 3 years in the blood.
- When a mosquito bites an infected dog, it takes in blood containing microfilariae. The microfilariae are then able to develop further only in the mosquito. The development process takes about 2 weeks, at which time the microfilariae mature into infective larvae.
- The mosquito carrying the infective larvae, deposits them in other dogs during blood meals. The larvae migrate to places under the skin, where they continue to grow for the next 3-6 months. By 6 months, the larvae have developed into adult heartworms and have migrated to the right side of the heart and lung vessels. Once within the heart, these young adult heartworms can start to produce microfilariae of their own.
Signs of heartworm disease may occur within 6 months of infection or may not appear at all. However, in most cases, signs will begin within 1 to 2 years after infection. Typically, infections result in coughing, labored breathing, weakness and tiring with exercise. Unfortunately, since the signs vary, the disease may be well advanced before the dog begins to show any problems, or the signs may be mistaken for another problem. In advanced stages, the signs become more frequent and severe. The heart and lungs can become severely damaged, as may the liver and kidneys. Eventually, heart failure can occur.
Your veterinarian will take a small blood sample to test for the presence of microfilariae and/or antigens to the adult heartworms. If your dog is infected, treatment should be started to eliminate the adult heartworms.
To control heartworms in the dog population and to provide your pet with the best possible protection against heartworms, the following guidelines are provided:
- All puppies should be started on preventative medication during the time of their vaccination series. The dosage must be adjusted as the puppy grows.
- All dogs should be tested on an annual basis, whether or not they are on a preventative medication, as nothing is 100%. It is convenient to have this done at the time of the yearly vaccinations.
- All dogs in our area should be on a preventative medication year-round. Missing just one month of the preventative medication can render your pet susceptible to infection.
- If your dog does have heartworms, it should be treated by a veterinarian as soon as possible to prevent permanent damage to the heart and lungs.
AS WITH ANY DISEASE, WE FEEL THAT PREVENTION IS THE BEST COURSE OF ACTION. IF AGGRESSIVE PREVENTATIVE AND MONITORING PROGRAMS ARE FOLLOWED, THE UNNECESSAY TREATMENT AND PERMANENT HEART AND LUNG DAMAGE CAN BE AVOIDED. IF YOU, AS AN INFORMED OWNER, FOLLOW THESE GUIDELINES, THEN YOUR PET WILL HAVE A SIGNIFICANTLY REDUCED RISK OF HEARTWORMS AND SHOULD HAVE A HEALTHY LIFE; FREE OF THESE PARASITES.