Once an isolated condition found only in warm southern climates, the heartworm epidemic has spread to all fifty states, and can be traced to every continent except Antarctica. Over 30 species of mammals, including dogs, cats, and humans have been known to become infected. Untreated dogs, especially those living within 150 miles of the Atlantic and Gulf coast, along the Mississippi, or those living in an area with high mosquito levels are especially at risk and need to be protected against this potentially deadly disease.
Heartworms are round worms known as nematodes which change through several stages before becoming adults. The larval stage, known as microfilariae, are spread from an infected dog to a mosquito when the mosquito feeds on the dog's blood. The mosquito serves as an intermediate host, and the worm must use the mosquito for several of its metamorphic changes before it can mature to adulthood. Depending on the weather, this process can take anywhere from ten days to six weeks. When the mosquito bites an uninfected host, it burrows into the skin and undergoes several more changes before it eventually moves to and inhabits the right side of the heart. The worms can live here for several years and can reach lengths from six inches in males to twelve inches in females.
Once mature, a female heartworm can give birth to thousands of live young every day. These young microfilariae remain in the bloodstream until taken in by a new mosquito host, sometimes for up to a few years. As the number of adult worms in an infected dog increases, they may spread into and affect the liver, lungs, and other areas of the heart. The disease in some animals, like cats, will mainly affect these other organs instead of the heart, causing severe respiratory problems.
This disease can be difficult to diagnose as its symptoms can take several months to begin to show. The effects and progression of the disease can vary, depending on the size and activity of the animal. Animals that place higher stress on the heart, like active working dogs, can have a more serious reaction with fewer worms present than a less active dog who does not cause as much stress on their heart. A soft cough is usually the first sign of heartworms, getting progressively worse until the animal may begin coughing up blood or fainting with the exertion it causes. Some animals may experience respiratory failure before heart failure as the worms spread to the lungs.
Your veterinarian will need to conduct blood tests to find the adult and microfilariae worms in your dog's system. They may also perform x-rays or other tests to see the extent of the infestation and complications it may be causing on other organs. Once diagnosed, separate treatments are needed to treat the adult and microfilariae forms. During treatment, the animal must remain inactive for several weeks to allow the worms to be absorbed by the body. Excess activity during this stage can cause the worms to become lodged in the lungs and cause respiratory failure in the animal. A month after the treatment for the adult worms, treatment begins to kill the microfilariae for up to two weeks if needed. A follow-up exam and series of tests is performed one year after treatment is completed to ensure that a new infestation has not occurred.
Many over-the-counter and prescription treatments are available to prevent the initial infestation. Preventative treatments vary from daily dosages to slow-release six month injections. Some of these treatments also help to prevent or repel fleas, ticks, and other parasites. Some treatments are applied topically to the skin, but most are oral. Preventing the infestation from occurring is more comfortable, less expensive, and much safer for the animal than undergoing weeks of risky treatments for a serious infection.
Like many other severe and potentially fatal diseases and parasites facing our pets today, heartworms can be prevented and eliminated with proper care. Having an animal vaccinated or given preventative treatment will save it from needing risky treatments and dying unnecessarily of complications from an adult heartworm infestation. If you live in a high risk area for this disease, have your dog tested and placed on a preventative method immediately. Inside the "danger zone" or out, see your veterinarian for more information on heartworm disease. It may save your pet's life.