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What is Heartworm
Disease?
Heartworm disease is
caused by infection of dogs (and sometimes cats) with the heartworm;
Dirofilaria immitus. The mosquito transmits the worms from pet to
pet. When the mosquito bites an infected pet and takes a blood meal, it
also ingests the immature form of the heartworm known as a
“microfilaria”. Once inside the mosquito, the microfilaria matures into
an infective larval stage of the heartworm. When the mosquito feeds on
an uninfected pet, the infective larvae are transmitted into the
animal’s blood stream. From there, the larvae circulate through the
body for up to 6 months as they mature. Then, they ultimately settle
down in the heart and arteries that supply the lungs (pulmonary
arteries). As the worms develop into adults, they can grow to be 2-3
inches in length. There presence in the heart and arteries obstructs
the flow of blood and causes inflammation of the blood vessel walls
which leads to their thickening. This causes the heart to work harder
to pump the same amount of blood, which eventually leads to
heart
failure. Occasionally, there may be so many worms in the heart that
they can lead to a complete obstruction of the blood vessels and acute
heart failure. The life cycle of the heartworm is depicted below:
What are the symptoms
of Heartworm disease?
It can take up to 2
years from the time a pet is infected with heartworms to the time
symptoms begin to show. Unfortunately, during this time, much of the
damage that occurs is irreversible. The symptoms that develop as a
result of heartworm infection are directly related to the failure of the
heart. They include:
How do we diagnose
heartworm disease?
A simple blood test that
can be run in the office can tell us if your pet is infected with
heartworms well in advance of any symptoms. If a pet is found to be
infected, then x-rays of the chest, ultrasound of the heart and blood
tests would be indicated. We recommend that all dogs be tested yearly
for the presence of heartworms.
Can Heartworm disease
be treated?
Heartworm disease can be
treated with drugs, which will kill the worms in the body. Once they
are dead, the body will slowly remove them. This treatment has risks
and can even cause the pet to die. While killing the worms is essential
to slow progression of the heart failure, it will not usually correct
the heart failure. Instead, various drugs must be employed to help
decrease the symptoms of heart failure.
Can Heartworm disease
be prevented?
 There are very safe and
effective drugs available that can be given once a month to prevent
heartworm infestation. We recommend a drug called Trifexis
for this purpose. It has the advantage of protecting dogs from
heartworm as well as fleas and intestinal parasites (roundworms, hookworms, and
whipworms). Before being placed on this drug, it is necessary to
have a blood test to check for the presence of heartworms in the body.
If they are present, then they must be treated before Iverhart
can be administered to prevent a severe reaction. We recommend that
all dogs in our area be placed on heartworm prevention starting as early
as 4 weeks of age.
Which pets are at
risk of developing heartworm infection?
Heartworm disease has
been found in San Bernardino and surrounding counties. We have
diagnosed and treated 2 cases in the past few months who have never been
out of this area. Pets that are subject to being bitten by mosquitoes
are at risk of getting infected. The mountainous areas around us
currently appear to have a higher incidence of heartworm infestation.
In our area, the risk of cats developing the disease is not very high.
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