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Allison is a
2-year-old short-haired cat who was adopted 2
days prior to coming to us. She was previously
a stray in the Detroit area. Allison came in because
she had intermittent episodes of coughing and
sneezing, and at times seemed to be having a difficult
time catching her breath. These difficulty breathing
episodes typically lasted less than 30 seconds.
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Allison (select to enlarge)
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On physical exam Allison was calm, alert and responsive.
Her heart sounded normal, with no murmurs or arrhythmias.
Her lungs sounded harsh on inspiration. The rest
of her physical exam was normal. Chest X-rays
and a feline heartworm test were recommended due
to the age and presentation of the cat. The owner
elected to start with a heartworm test initially,
and follow-up with X-rays at a later date. Feline
heartworm tests are sent out to a specialty lab
where they test for antigen and antibody to the
heartworms themselves. The antigen that is tested
for is a protein that is produced by the female
heartworm itself, and a positive result indicates
that a cat is infected with adult female heartworm,
or that the cat has been recently infected with
adult female heartworm but the infection had recently
cleared. The antibody heartworm test detects circulating
proteins that the cat immune system produces to
attack the heartworms. A positive result indicates
adult heartworms are present or have recently
been cleared.
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Allison's heartworm antigen
and antibody tests both came back positive, indicating
a current or recent infection. Allison came in
for a recheck appointment so that follow-up X-rays
could be performed to see the extent of involvement
with the heart and lungs. Allison's X-rays revealed
a severe bronchial pulmonary pattern in the lungs
as well as a very prominent pulmonary artery of
the heart and a mild amount of heart enlargement.
Her right caudal lung lobe showed a lesion that
could be consistent with the presence of a worm,
possibly dying off.
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Chest Radiograph (select
to enlarge)
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The results of Allison's X-rays were
consistent with an active heartworm infection. Unfortunately
there is no good treatment for heartworm disease
in cats. The treatment options that are available
in dogs could cause sudden death in a cat, and therefore
prevention of infection is the only way to be sure
that a cat can survive heartworm disease. Heartworm
prevention comes in oral tablets or topical products
that can be given once monthly to prevent an infection.
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Heartworm disease is transmitted by mosquitoes.
The mosquito bites an infected animal and 'ingests'
baby heartworms, it then bites an uninfected animal
and the baby heartworms are injected into the
healthy animal. The baby heartworms migrate through
the circulation system of the animal until they
get to the heart, where the heartworms grow to
be adults and cause congestive heart failure.
These adult heartworms produce baby heartworms,
which then migrate through the circulation system
and the cycle perpetuates itself. (Oftentimes
in cats, heartworms do not reproduce, whereas
they do in dogs.)
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Chest radiograph
(select to enlarge)
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The more common manifestations of heartworm
disease are difficulty breathing, lethargy or
sudden death, and occasionally we will see coughing.
Oftentimes cats will show no clinical signs of
heartworm disease until the heartworms begin to
die off, which can result in a severe allergic
reaction.
Because the death of heartworms causes a severe
allergic reaction in cats, and this is what can
often cause death, we treat the allergic component
of the heartworm disease in cats with steroids
to help prevent a severe allergic reaction as
they die off. Allison is currently being monitored
on a steroid, and her owner is watching her closely
for signs of difficulty breathing and coughing.
The heartworms take 18-24 months to die off, and
they will die off on their own. Most cats do very
well, but we can see episodes of severe allergic
reaction and death even on a steroid. Allison
is currently doing very well.
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