What is heartworm? Symtoms and treatment

Heartworms, Dirofilaria immitis was once considered a parasite of southern climates, however is now considered a a serious, worldwide pest affecting dogs, cats, wolves, coyotes, foxes, and some other animals. From its discovery in dogs more than a century ago and the documentation in cats in the 1920s, researchers have devised diagnostic tests, preventives and treatments, but the disease has spread to all 50 states. According to the Heartworm Society, the highest infection rates occur in dogs (not maintained on heartworm preventive) within 150 miles of the Atlantic and Gulf coasts and along the Mississippi River and its major tributaries. Other areas with large mosquitoe populations also have a high rate of infestation.

Heartworms belong to the same class of worms as roundworms. In fact, they look a bit like roundworms, but that is where the similarity ends.

Dogs and cats can only be infected by the bite of an infected mosquito. There’s no other way dogs get heartworms. And there’s no way to tell if a mosquito is infected. That’s why prevention is so important.

Both male and female live within the chambers of’ the heart, usually extending through the valves. The worms prohibit proper valve closure as blood is pumped from one chamber to the next, seriously impairing the operation of the heart. In heavy infestations the woworms in infected dog heartrms migrate up the pulmonary artery and clog the blood vessels of the lungs.  Upon reaching the heart, the young adults continue to grow. Up to now there has been no evidence of disease in the dog. It is only after adult worms mate and start to discharge tiny motile microfilariae that circulate in the blood that disease becomes apparent. Microfilariae appear in the blood about 200 days after infection.

Typically the symptoms of heartworm infestation include:

· Coughing

· Inability to exercise without wheezing, coughing or retching

· Abnormal lung sounds

· Loss of consciousness

The treatment of heartworm starts with the administration of parasite-killing drugs. This is a two-step process.  The adult worms and the microfilaria are eliminated separately.  No one medication kills both.  The adults are treated first then a different treatment is used to kill the microfilaria and migrating larvae.

Before making the decision to treat a heartworm infection, the stage of the disease must be evaluated. Heartworm disease is broken into three classes:

* Class one - asymptomatic to mild heartworm disease symptoms
* Class two - moderate heartworm disease symptoms
* Class three - severe heartworm disease symptoms

The most serious side effects commonly occur with the treatment of the adult worms.  As the worms die they lodge in the lung arteries and block even more blood vessels than before treatment.  Besides the usual inflammation caused by the presence of the worms, the inflammation is amplified due to the decomposing worms within the blood vessels.  This worm destruction releases foreign substances in to the dog’s circulation as the worms break down and are eliminated from the dog by the immune systems.  A large amount of inflammation and swelling generally occurs during this period.