Heartworm infections are less common in cats than in dogs, in fact they
are likely accidental hosts as their bodies to not provide an ideal host like the body of a
The heartworm, Dirofilaria immitis, infection begins when larvae in the mouthparts of a mosquito enter the cat
through a bite. They burrow beneath the skin, molt twice and become small, immature worms. The first molt
occurs 1-12 days after the bite. They remain in this phase for up to 68 days before molting again to become the
worms. These worms then make their way into a peripheral vein where they are carried to the right ventricle of
the heart and the pulmonary arteries. In cats, they may also become disoriented and move into body cavities and
the central nervous system. Approximately six months after entering the hosts body, they mature into adults
that can be up to 12 inches long and live for two to three years.
Mature heartworms produce larvae, called microfilaria, that circulate in the blood stream.
This is much less common in cats than dogs, possibly because the cat’s immune system kills the larvae off
Symptoms of Heartworm Disease
Cats have a very small heart, so even a small infestation of only one or two worms can be enough to cause very
serious heart trouble or even sudden death. Symptoms can include a cough made worse by exercise, lethargy,
sudden weight loss and change in coat condition, and bloody sputum or phlegm. It may appear that the cat as
asthma or allergic bronchitis.
If the cat survives this phase, they should be fine until the worms die in two to three years. During this
phase, symptoms including labored breathing and other low-grade but chronic respiratory signs may occur,
congestive heart failure, heart murmur, loss of appetite and change in coat condition may occur again, as well
as intermittent vomiting. If an autopsy is performed, worms may be discovered.
Diagnosis is simple and is generally performed through a blood test that looks for the heartworm antigen and
antibodies. X-rays and echocardiography are also helpful in making a diagnosis
How To Prevent A Heartworm Infection
Heartworms are spread by mosquito’s, so the best way to protect your cat from heartworms is to remove the
threat of mosquito’s. Even indoor cats can be infected if a mosquito makes its way inside. There are also a
number of products that can be administered to help prevent heartworms: Revolution, Heartgard, and Interceptor
are three of the better known.
Your cat does not have to be tested before these preventative measures can be
administered, but it is certainly recommended.
At this time there are few treatments for cats with heartworms. Ivermectin is used but it is still considered
an experimental treatment, and surgery can be utilized but it is very risky. It is best to simply use
preventative measures and be careful in eradicating mosquitos from around your home.
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