Heartworm disease is caused by infection with the parasitic worm difilaria. This disease most commonly affects dogs of all ages, but has been reported rarely in cats. Heartworm disease is spread by infective larvae that are transmitted by the bite of an infected mosquito. The larvae mature, live, and reproduce in the pulmonary artery and right ventricle of the heart. The movement and space occupying effects of the worms cause scarring, thickening of the pulmonary artery and other affiliated vessels, as well as scarring and enlargement of the right ventricle of the heart. This combination predisposes the patient to acute death from clot formation or often results in right sided heart failure. Heartworm disease occurs in all areas where mosquitos persist at least part of the year, placing dogs nearly nationwide at risk. Dogs that live in sub-tropical to tropical areas where mosquitos persist year round are particularly at risk. In the State of Florida, for example, hearworm disease is an endemic problem.
The heartworm positive patient often presents with no symptoms at all and is discovered on routine testing regularly performed at the yearly visit. The reason for this is that, unless clinical disease results from clot formation or allergic reaction, it can take several years before chronic changes are observed. Clinical disease is most commonly found in patients who's owners who do not participate in yearly visits, heartworm preventative medication, or vaccines; or, in stray dogs. Patients showing clinical disease present with symptoms including chronic non-productive cough, lethargy and excercise intolerance, syncope (fainting spells), trouble breathing, free fluid in the abdomen (known as ascites), or acute sudden death.
Treatment for heartworm disease is by injections of an arsenic - like drug called Melarsamine. Given the toxic nature of routine blood screening is necessary before treatment. Treatment is in most cases successful, although complications arising from toxicity of the treating drug or reactions to the dead worms sometimes occur. Treatment is always most successful when the disease is caught early, before clinical disease has set in. Therefore, if your dog has never been tested for heartworm disease before, or, more than one year has elapsed since the last test, the dog should be tested A.S.A.P.
Thankfullly, heartworm disease is easily prevented by administration of an oral monthly medication. A number of effective products are available through your veterinarian, including: Heartgard, Interceptor, and Sentinel. Yearly heartworm testing is always recommended as, while the preventative treatments are very effective, nothing is 100 %.
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