Heartworm (Dirofilaria immitsi) disease primarily affects dogs, but also affects cats. Heartworm infection can significantly damage the heart, lungs, and other organs, and can be fatal if left untreated. Heartworm infection is transmitted through mosquito bites: a mosquito bites an infected dog and ingests heartworm larvae (microfilaria), which are passed to the next dog it bites. Microfilaria penetrates the dog's skin and travel through the body to the heart. It usually takes a few months for the infection to reach the heart; once there, the worms can grow to 14 inches.


Common symptoms of heartworm infection in dogs include:

* Coughing
* Diminished strength and vitality
* Lethargy

Severe infestation can cause sudden death. Heartworms can

* obstruct the heart chambers and blood vessels,
* lead to the development of pulmonary hypertension (high blood pressure), and
* cause heart failure.

Diagnosis is made by testing a small blood sample for the presence of microfilaria (heartworm larvae) or heartworm antibodies (proteins that defend the body against infection).

Treatment depends on the severity of the disease and usually involves administering 2 doses of injectable Immiticide�.

Several preventative monthly medications are available (e.g., Sentinel�, Interceptor�, Heartgard�). These medications are generally safe and can be administered year round, depending on the risk for the disease in certain geographical areas.

Cats and heartworm
Cats are not natural hosts for heartworms and the risk for infection is lower than in dogs; however, cats can develop heartworm disease. According to the American Veterinary Medical Association, heartworms can cause severe reactions and death in cats. Heartworm infection in cats occurs more often in warm climates and in areas where dogs are at a increased risk.

Symptoms of heartworm in cats include the following:

* Breathing difficulties
* Coughing
* Lethargy
* Vomiting
* Weight loss

These symptoms are easily confused with other disorders, especially bronchial asthma, making feline heartworm infection difficult to diagnose.

There is no approved product for treating heartworm infection in cats. Infected cats may suffer symptoms and die even after treatment.

Pet owners who are concerned about heartworm infection should discuss prevention with their veterinarian. A monthly preventative medicine is available, depending on the risk for the disease in cats in certain geographical areas.