General Information
Heartworm disease is transmitted by mosquitoes. This disease cannot be transmitted directly to other animals, however animals affected with hearworm disease act as a reservoir of potential infection for other animals in the area. Although named as such, heartworms normally do not live in the heart, but actually live in the arteries inside the lungs.
Diagnosis
Heartworm disease is generally diagnosed by a blood test, which is recommended annually. When a positive test result is obtained, thoracic radiographs are recommended to evaluate for changes to the lungs and blood vessels in the lungs. Depending on symptoms, or if heart enlargement is seen on radiographs, an echocardiogram may be recommended. Full lab work (complete blood count, biochemistry panel with electrolytes, and urinalysis) is indicated to evaluate overall health prior to treatment for heartworm disease, and also to evaluate for possible complications associated with heartworm disease.
Complications and Sequelae
Pets associated with heartworm disease are often asymptomatic. However heartworms can cause a significant inflammatory reaction in the lungs, leading to build-up of inflammatory cells and debris in areas around the airways and even inside the airways. This can lead to coughing, wheezing, difficulty breathing, and can also contribute to making PH worse.
While present, the heartworms cause irritation to the walls of the arteries in the lungs, leading to increased blood pressure in the lungs, or pulmonary hypertension (PH). PH makes it more difficult for blood to flow through the lungs and pick up oxygen to be taken to the vital organs. This leads to clinical signs of difficulty breathing, cyanosis (blue gums), weakness, lethargy and collapse.
Kidney insult can also occur with heartworm disease secondary to poor blood flow to the kidneys and clumps of antibodies that do damage to the filtration system in the kidney. This leads to protein in the urine, which contributes to ongoing kidney damage.
Rarely, a mass of heartworms can migrate backwards into the heart, and obstruct blood flow through the heart. This causes sudden weakness, lethargy, intolerance to exercise, episodes of collapse, and abdominal distension. In addition, difficulty breathing and cyanosis (blue gums) can be seen. Red blood cells are damaged as blood flows through the mass of worms, which ultimately leads to anemia (low red blood cell count) and discoloration of the urine (port wine color).
Treatment
Immiticide therapy is the treatment of choice for dogs, and consists of intramuscular injections (deep lumbar). A “split protocol” is recommended to facilitate a slower kill of adult heartworms, which decreases (but does not eliminate) the risk of life-threatening complications as the worms die. The first injection is followed by a one month period of exercise restriction and cage confinement (with short leash walks only); during this time, the male adult heartworms die off and the body takes its time to clean up the debris. After one month, your dog will return for two injections given 24 hours apart. Thereafter, they will again be exercise restricted and cage confined for one month. As Heartgard is a preventative drug, this should be continued indefinitely and without interruption. Heartgard also causes slow kill of the microfilaria (heartworm larvae) in the bloodstream.
Prevention
There are multiple heartworm preventative medications, which are given monthly, either orally or topically. Please consult with your veterinarian and/or cardiologist regarding the best preventative medication for your pet.
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