Most pet owners are aware of heartworms and the fact that heartworms can infect dogs. However, fewer pet owners realize that heartworms can also be a threat to cats.
How Do Cats Become Infected with Heartworms?
As in dogs, cats become infected with heartworms when bitten by an infected mosquito. The infected mosquito injects a larval form of the heartworm into the cat. Eventually, usually roughly 3-4 months after infection, the larval heartworms find their way to the arteries and blood vessels in the lungs. There they may continue to develop into adults and will begin to reproduce as well, producing a larval form of heartworm called microfilaria.
However, cats are more resistant to heartworm infections than dogs. As a result, there are differences in the way feline and canine infections occur and differences in the clinical disease they cause as well.
Cats usually have far fewer adult heartworms than dogs. In fact, an infected cat may have only one or two adult worms whereas an infected dog may have dozens, even hundreds.
Cats also rarely have circulating microfilaria in their blood stream. Infected dogs usually do unless they are treated with medication to kill the microfilaria. Apparently, the feline immune system is more efficient in finding and killing the heartworm microfilaria than the canine system.
Symptoms of Feline Heartworm Disease
Though heartworm infection is somewhat different in cats than in dogs, the result is no less dangerous.
Cats infected with heartworms often develop respiratory symptoms in response to the presence of the immature heartworms in the lungs. This has become known as heartworm-associated respiratory disease, or HARD.
Heartworm-associated respiratory disease is frequently misdiagnosed or confused with feline asthma. The symptoms are similar and making the distinction between the two diseases can be difficult.
Symptoms seen with feline heartworm disease include:
- lack of appetite
- weight loss
- difficulty breathing
- rapid breathing
- sudden death
Diagnosis of Heartworm Disease in Cats
Diagnosing heartworm infections in dogs is a relatively easy procedure. However, in cats, the diagnosis is more difficult.
Complicating diagnosis is the fact that many of the symptoms seen in feline heartworm disease are a result of immature heartworms and the damage they produce in the lungs.
- Blood tests that are frequently done to help diagnose feline heartworm disease include the heartworm antigen test and the heartworm antibody test. The antigen test detects a protein in the cat’s blood that is created by the heartworm itself. The antibody test detects a protein that the cat’s body produces in response to the heartworm. However, neither of these tests are 100% accurate in diagnosing an active heartworm infection. Frequently, both tests are performed to aid in diagnosis.
- Chest radiographs (xrays) are sometimes recommended to evaluate the size and shape of the heart and the extent of damage to the lungs.
- An echocardiogram (an ultrasound-based study of the heart) can be useful in detecting any adult heartworms living within the heart of the cat.
Treatment of Heartworm Disease in Cats
There is no cure for heartworms in cats. Treatment is symptomatic and based on the the cat’s physical condition and clinical signs.
- Corticosteroids such as prednisolone are frequently used to control the inflammatory process in the lungs of the infected cat. These medications are generally used when there is evidence of damage to the lungs in an otherwise stable cat.
- For cats with more severe signs of heartworm disease, intravenous fluids, oxygen administration, bronchodilators (medicines used to open the airways), antibiotics, and other medications may be needed in addition to hospitalization and nursing care.
- In rare instances, surgical or endoscopic extraction of the heartworms from the heart or vena cava (the large vessel leading from the heart) may be attempted.
Preventing Feline Heartworm Infections
There are various medications that may be administered monthly to your cat to prevent heartworm infection. Consult your veterinarian for advice about which medication is best for your cat.
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