Heartworm Disease in Dogs
Canine Heartworm - A Disease Caused by Worms in the Heart of a Dog
May 3, 2009
Heartworm disease in dogs is caused by the bite of an infected mosquito. Heartworms are actually nematode worms which are called Dirofilaria immitis. Adult heartworms live inside of the heart of an infected dog.
The Life Cycle of the Heartworm - How Dogs Become Infected
Mosquitoes bite in order to feed on the blood of their victim. When a mosquito feeds on the blood of a dog infected with heartworms, that mosquito then becomes infected with heartworms also. When the mosquito then feeds on another dog, the mosquito can pass heartworms on to the dog which he is feeding on.
Mosquitoes are infected with microfilaria, a larval form of heartworm, when feeding on an infected dog. As time progresses, the heartworm microfilaria develops into an infectious stage. When the infected mosquito feeds on another uninfected dog at this stage, the microfilaria can then be passed on to that dog. Once inside the dog, the heartworm microfilaria continue to develop and mature and eventually reach the heart, where the heartworm finishes its maturation cycle.
The length of time necessary for the microfilaria to develop into an adult heartworm is normally four to six months. During that four to six month time period, standard heartworm blood tests will usually remain negative.
Symptoms of Heartworm Disease in Dogs
Canine heartworm disease is characterized by damage to the heart caused by the worms which live inside the heart of the infected dog.
Infected dogs can have hundreds of adult heartworms living inside of the heart. Symptoms caused by heartworm infection in dogs include:
- difficulty breathing
- coughing
- exercise intolerance
- depression
- listlessness
- fluid accumulation with the abdomen (ascites)
- fainting (syncope)
How is Heartworm Disease in Dogs Diagnosed?
Heartworm disease is usually fairly easily diagnosed by heartworm blood tests which detect an antigen to heartworms within the blood of the infected dog.
Evaluation of the heartworm positive dog may also include:
- routine blood screens
- radiographs of the chest
- ultrasonography of the heart
Treatment of Heartworm Disease in Dogs
Treatment of dogs infected with heartworms and suffering from heartworm disease involves injections of a drug known as Immiticide. Immiticide is an arsenic compound which is injected into the muscle of the heartworm infected dog.
Heartworm treatment in dogs is unpredictable with no guarantee of success. Some dogs remain infected with heartworms even after treatment with Immiticide, though the numbers of heartworms may be reduced from the previous pre-heartworm treatment level.
Prevention of Heartworm Disease in Dogs
Prevention of heartworm disease is dogs is a fairly simple task. There are many heartworm preventive medicines which are effective in keeping dogs free of heartworm infection. Most heartworm preventive medications are administered monthly. Options include chewable tablets, non-chewable tablets, topical spot-on medications and, in one case, an injection which is repeated every six months (Proheart 6).
Most heartworm medications are considered to be very safe and very effective. The use of Proheart 6 remains controversial because of prior adverse reactions which originally lead to the product being recalled. It has been relicensed for use in dogs as a heartworm preventive medicine but it currently has conditional licensure by the FDA which governs the usage of the product. Many veterinarian feel that the monthly options are safer for dogs, but there are also a significant number of veterinarians who believe the Proheart 6 injection to be safe if used under optimal conditions.
One certainty about heartworm disease in dogs remains. Heartworms are much more easily prevented than treated. Heartworm treatment is risky and not always successful and heartworm infections can be fatal for dogs.
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