HEARTWORN DISEASE IN DOGS Prepared and released by the AMERICAN HEARTWORM SOCIETY WHAT IS HEARTWORM DISEASE? Canine heartworm disease develops when a dog is bitten by a mosqito carrying microscopic heartworm larvae (juvenile worms) of a parasite called Dirofilaria immitis. As a mosquito feeds, these microscopic larvae are deposited on the dog and quickly penetrate the skin to begin their migration into the dog's bloodstream. Adult heartworms can grow 10 to 12 inches in length and make their home in the right side of the heart and pulmonary (lung) arteris, often causing lung disease and heart failure. Although easy to prevent, heartworm disease continues to be a major health problem for dogs living in the United States and throughout the temperate and tropical regions of the world. HEARTWORM LIFE CYCLE When a dog or other suitable host has a mature heartworm infection, female worms releae their young (microfilariae) directly into the animals bloodstream. When a susceptible mosquito bites an animal with microfilariae in the blood, it ingests the microfilariae along with the blood. Over the following 10 to 14 days, these microfilariae develop and mature into infective larvae inside the mosquito. When the mosquito bites another dog, the larvae are left behind to enter the fresh wound. In six to seven months, these microscopic larvae migrate to the heart and vessels of the lungs where they can grow up to a foot long.The larvae also become sexually mature and produce microfilariae of their own, which are availble in the dog's blood to other mosqitoes. SIGNS OF HEARTWORM DISEASE Since some dogs can be infected for many years before symptoms develop, heartworm disease in dogs may not be obvious. But, as heartworms slowly cause damage to the pulmonary arteries of the lungs, signs of disease may include a mild persistent cough, reluctance to exercise, fatigue after moderate activity, decreased appetite, and weight loss. Eventually, as blood flow through the diseased lungs becomes more restricted, some dogs can develop heart failure. This is commonly recognized by a buildup of fluid in the abdomen and the apperance of a "swollen belly." Although less common, a large number of heartworms can lead to a sudden obstruction of blood flow through the heart and longs. This blockage often becomes a life-threatening form of cardiovascular collapse and is referred to as "caval syndrome." Symptoms of caval syndrome often include a sudden onset of labored breathing, pale gums, dark red or "coffee-colored" urines, and an inability or unwillingness to move. Without prompt surgical removal of the heartworm blockage, few dogs suffering from caval syndrome survive. DETECTING HEARTWORM INFECTION Numerous blood tests are available for detecting heartworm infections in dogs, and your veterinarian will perform the test most appropriate for your dog. WHO SHOULD BE TESTED? Annual testing is recommended for monitoring the success of any heatworm prevention program. Sometimes, individual risk factors, clinical signs, preventive changes and testing limitations might warrent more frequent testing. TREATMENT There are several things to consider once a dog is diagnosed with heartworm disease. Without treatment, heartworm disease will worsen and may lead to more serious illness. Unless medical reasons identify a dog as a poor candidate, heartworm-positive dogs should be treated. A thorough physical examination, radiographs, and blood and urine tests may be needed prior to treatmentto asses your dog's level of risk to serious health issues after treatment. PREVENTION Heartworm preventives are effective when given properly and on a timely schedule. It is important to monitor your pet's weight to insure your pet falls within the weight range listed on the package. All approved heartworm preventives are highly effective, safe, easy to use, relatively inexpensive, and often provide treatment for additional parasites. Prevention is always more safe and affordable than treating dogs with adult heartworm infections. Please remember, it is your responsibility to faithfully maintain the program you have selected in consultation with your veterinarian. The best way to eliminate the risk of heartworm infection in your dog is to institute a year-round prevention program. Be certain to have all pets tested prior to initiating or restarting any heartworm prevention program, as administration of some preventives can cause life-threatening reactions when given to heartworm-infected pets.