Both dogs
and cats are susceptible to heartworm infection from mosquitos. However,
the unique differences between each species means that heartworm disease
in cats is very different than in dogs. Cats are not a
natural host for the heartworm parasite, Dirofilaria immitis. So, when a
cat is bitten by an infected mosquito, the cat’s immune system is able to
kill most of the immature worms (microfilaria) before they reach adult
life stages. Therefore, only a few worms usually reach adulthood in
cats. Heartworms thrive in dogs, however, because dogs
are a natural host of heartworm. A dog may have upwards of
50 worms inside him.
Unfortunately,
it takes only one adult worm in a cat to cause clinical signs
such as respiratory distress, coughing, vomiting, and even death.
Furthermore, the immature worms and the cat’s own immune response to them
can cause asthma-like lung disease with lifelong symptoms, known as
Heartworm Associated Respiratory Disease (HARD). In dogs, it
is usually only the adult worms that cause problems by damaging the heart
and surrounding blood vessels. These dogs often develop
a cough, which can progress to difficulty breathing, weight loss, and
ultimately heart failure and death.
Heartworm
is easily diagnosed in most dogs with a simple blood test which detects the
presence of adult worms. Because infected cats usually only
have 1 to 3 worms in their bodies, there are often too few worms for the
blood tests to detect. Diagnosing heartworm infection in cats
can be very challenging because false negative test results are common. When a
dog is diagnosed with heartworm, there is an FDA-approved medication to
eliminate heartworms. However, since there is NO approved treatment for
heartworm infection in cats, the best we can do is try to manage the cat’s
condition and symptoms. The good news is that heartworm is easily
preventable in BOTH cats and dogs with year-round medication.
- By: Stephanie Brittin,
DVM
