Heartworm disease is less common in cats than in dogs because cats
are not the 'natural' host for the heartworm parasite,
Dirofilaria immitis. However, any cat living in or visiting an area
that has mosquitoes and infected cats is at risk of getting
heartworm disease. When they do become infected, cats with
heartworm disease typically show less severe signs than dogs with
the disease. However, heartworm disease in cats can be quite
dangerous, even deadly.
What's the Heartworm Hype?
Heartworm infection in cats does not follow the same pattern that
is seen in dogs. Immature heartworms, called microfilariae, do not
survive well in cats. Likewise, mature worms do not live as
long-just 2 to 3 years in cats as opposed to 5 to 7 years in dogs.
Also, fewer worms migrate to the cat's heart, and they are
generally smaller than the worms found in dogs. This makes them
much harder to detect.
Yet just one worm can cause big problems in cats because of the
small size of the cat's blood vessels. The primary sign of
trouble is inflammation of the arteries and tissues around the
lungs. Other signs of heartworm disease include gagging or
vomiting, weight
loss, and lethargy.
When the worms die, they sometimes block blood vessels. Depending
on which vessels are blocked and the amount of inflammation
involved, significant portions of the lungs can
be affected, causing sudden, severe breathing difficulty for the
cat and possibly even sudden death.
Diagnosing and Treating the Disease
Detecting
immature or adult heartworms in cats is more difficult than in
dogs, as there is no single reliable test to diagnose the disease.
In addition to evaluating your cat based on clinical signs and
performing a physical examination, your veterinarian may conduct a
number of different tests, including blood work, x-rays,
electrocardiograms (EKGs), and/or echocardiograms. Even then,
however, results may be inconclusive.
If your cat is diagnosed with heartworm disease, your veterinarian
will determine the best treatment approach based on the nature and
severity of your cat's infection. The medications used to treat
heartworm disease in dogs are not commonly used in cats
because of serious side effects, including respiratory problems and
even death due to blockage of vessels when the worms die. Many
veterinarians instead choose conservative
treatment, which focuses on managing the signs of the disease until
the worms die (about 2 years). Some veterinarians opt to remove the
worms surgically.
Preventing Heartworm
All cats can be exposed to mosquitoes, even indoor cats, but
keeping your cat inside certainly reduces the likelihood that he
will come into contact with an insect carrying the parasite. Your
veterinarian can also prescribe an oral or topical medication that
prevents heartworms from maturing and reproducing.
THE HEARTWORM LIFE CYCLE IN CATS
• A
mosquito ingests tiny, immature worms, called microfilariae, in a
blood meal from a heartworm-infected host animal.
• The microfilariae develop inside the mosquito, becoming
infective larvae within 2 to 3 weeks.
• The mosquito transmits the infective larvae when it bites a
new host.
• The larvae develop inside the cat's body tissues, then
enter the bloodstream and move toward the heart and blood vessels.
The larvae grow into adult worms inside the heart, where they will
live until they die (about 2 to 3 years).
• In some cats, female worms release microfilariae into the
blood, and the cycle starts again.
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