Canine Heartworm Disease
Heartworm disease is caused by the parasitic nematode (worm) Dirofilaria immitis.
The adult form of the parasite can reach six to 12 inches in length, and resembles a piece of cooked spaghetti.
Heartworms live primarily in the dog's large pulmonary arteries and within the heart itself.
How exactly do they get there? Heartworm disease is carried and transmitted by our friend, the mosquito. A mosquito carrying the infective form of the heartworm larva bites the dog, transferring the larva to the bite wound.
The heartworm larva then undergoes several stages of development within the subcutaneous (just beneath the skin) tissues, and migrates through the circulatory system to the right side of the heart.
Adult heartworms are present in the heart approximately four to six months after the bite of an infected mosquito. After reaching the heart, the parasites produce microscopic larva called microfilariae, which are released into the dog's circulation.
These microfilaria can be picked up by another mosquito when it bites the affected dog. The microfilaria then develop into infective larvae within that mosquito, and the life cycle is ready to repeat.
Clinical signs of heartworm disease in an affected dog include coughing, weight loss and exercise intolerance. However, some cases may show no clinical signs.
Fortunately, there are a number of readily available, excellent tests for heartworm disease. Antigen tests are the preferred type. They are run on a blood sample, and test for the presence of a protein produced by the adult worms. Antigen testing is preferred over testing for the presence of microfilaria, as up to 20 percent of dogs with heartworm disease do not have microfilaria present in the circulation.
Treatment of a dog with heartworm disease can be complex, and may involve additional diagnostic procedures such as chest radiographs (X-rays) and blood profiles. There are two drugs available to treat heartworm disease, melarsomine and thiacetarsamide.
After treatment, it is vital that the dog be confined and have its exercise restricted to short leash walks for the first month. Exercise restriction helps reduce the incidence of thrombo-embolic pneumonia, a potentially serious complication of heartworm disease which can occur as the heartworms die and break apart within the pulmonary circulation.
Left untreated, heartworms can cause severe pathologic changes within the heart and lungs, and possibly lead to heart failure and even death.
Now for the good news about canine heartworm disease: it can be easily prevented! Most vet practices will test adult dogs for heartworm in the spring months, and then place them on a monthly heartworm preventative medication that the owner administers at home.
An additional benefit of the heartworm preventative is that it helps control intestinal worms such as roundworms and hookworms as well.
Canine heartworm disease is a potentially life-threatening parasitic disease of dogs that is much more easily prevented than treated. Please contact your family veterinarian and follow his/her recommendations regarding heartworm disease and your dog's health.