Heartworm is a serious, life-threatening disease of dogs. It is due to the presence of the adult stage of the parasite, Dirofilaria immitis, in the pulmonary arteries and right ventricle of the dog's heart. Until the early 1970s, the occurrence of heartworm in the United States was primarily confined to the southeastern part of the country. Today, it is found almost everywhere in the continental United States and is a major threat to the dog population of Canada.
After the microfilariae have gone through their development, they are ready to infect a new victim. During a blood meal (mosquito bite), the mosquito injects the microfilariae into a new dog. These small, microscopic worms migrate under the skin and eventually enter the dog's blood stream. About 6 months after the initial mosquito bite, the microfilariae arrive at the heart. The final maturation and the mating of the heartworm occur in the pulmonary arteries. The adult worms live in the pulmonary arteries and right side of the heart, where they can survive for several years.
What Are the Signs of Heartworm Disease?
For both dogs and cats, clinical signs of heartworm disease may not be recognized in the early stages, as the number of heartworms in an animal tends to accumulate gradually over a period of months and sometimes years.
Recently infected dogs may exhibit no signs of the disease, while heavily infected dogs may eventually show clinical signs, including a mild, persistent cough, reluctance to move or exercise, fatigue after only moderate exercise, reduced appetite and weight loss.
Cats may exhibit clinical signs that are very non-specific. Chronic clinical signs include vomiting, gagging, difficulty or rapid breathing, lethargy and weight loss.
Not only is heartworm dangerous, but the treatment for heartworm disease is dangerous as well.
Administration of preventive medication is the best method for keeping a dog free from heartworm disease.