How to Protect Your Pet from Heartworm Disease
Symptoms and Treatment of Dirofilaria Immitus
Nov 25, 2008
Heartworm disease is caused by an organism called Dirofilaria Immitus, found in the nematode family. It can be transmitted by up to 70 different species of mosquitoes. The adult heartworms primarily reside in the pulmonary artery and the right ventricle of the heart. The pulmonary artery is the main artery which carries blood from the lungs to the heart. The worms damage the artery walls, cause scarring and lesions in the lungs, and may obstruct the arteries if there is a high worm burden (Merck and Co., Inc, 2008).
There are five classes of heartworm disease in dogs, depending on the severity of infection and symptoms. They range from class I, which has mild symptoms to class IV, where the disease is usually fatal without emergency surgery.
Symptoms in Dogs (Merck and Co., Inc, 2008)
Heartworm symptoms usually appear 5-6.5 months post infection and often correlate with the dog’s activity level. For example: a hunting dog may show no signs of infection, until taken out hunting. Symptoms include:
- Coughing
- Excersize intolerance
- General state of illness
- Difficulty breathing
- Blue mucus membranes
- Fainting
- Bloody nasal discharge, or sneezing of blood
- Fluid in the Chest Cavity
Symptoms in Cats (Merck and Co., Inc, 2008)
- May show no symptoms
- Coughing
- Dyspnea
- Vomiting
- Anorexia
- Weight loss
- Death as a result of respiratory distress, shock, and blood clots or worms lodged in the pulmonary artery, which obstructs blood flow to the lungs.
Diagnosis
In dogs, heartworm is easily diagnosed by a snap test, which detects the presence of heartworm antigen from female worms in the dog’s blood. This test can be run at the dog’s regular veterinarian, and is often a regular part of yearly physical exam and vaccines. Heartworm larvae or microfilaria, can also be occasionally seen on a blood smear, wound around cells.
The snap test in cats is not a reliable indicator of heartworm. Therefore heartworm disease is usually diagnosed by x-rays, a physical exam, blood serum tests, and echocardiography. The American Heritage Science Dictionary describes an echocardiogram as, “An ultrasound image of the heart that demonstrates the size, motion, and composition of cardiac structures and is used to diagnose various abnormalities of the heart.”
Treatment in Dogs
Current treatment in dogs according to the Merck Veterinary Manual is an injection of melarsomine dihydrochloride, usually given in two doses 24 hours apart. The doses may also be given as a first injection and then in one month, the next two doses at 24 hour intervals. This latter method is considered safer, especially in dogs with a high-worm burden. In some cases, it is also recommended to first give a dose of ivermectin 1-6 months before the injections of melarsomine dihydrochloride. This lessens the number of microfilaria, stunts immature heartworms, and reduces the female worm mass. Following treatment, exercise is severely restricted, and the possibility of serious and sometimes fatal complications is a very real concern.
In very severe cases, surgical removal of worms from the right atrium and tricuspid heart valve may be the dogs only chance at survival.
Treatment in Cats
There is currently no satisfactory treatment for cats, making the infection often lethal, and there are many complications. Many cats are managed with restricted activity and steroid therapy. The Merck Veterinary Manual estimates that approximately 25-50% of patients survive. Surgical removal of the worms may also be attempted if the worm burden is high.
The good news is that heartworm disease is completely preventable with a regular preventative such as Heartguard or Proheart. Year-round medication is recommended especially in warmer climates, along with an annual heartworm test. It is recommended that all cats and dogs be placed on regular preventative regardless of whether the pet goes outside or not.
For more information about heartworm disease read: Heartworm Disease in Pets
Works Cited
echocardiogram. (n.d.). The American Heritage® Science Dictionary. Retrieved November 19, 2008, from Dictionary.com website: http://dictionary.reference.com/browse/echocardiogram
Merck and Co., Inc (2008). Heartworm Disease: Introduction. Retrieved November 3, 2008 from The Merck Veterinary Manual. www.merckveterinarymanual.com.
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