Canine Heartworm Disease
Reprinted
courtesy Connecticut Veterinary Medical Association.
Copyright
©1996, 1997 HomeVet
What
Is It?
Canine
heartworm disease [also called dirofilariasis (dir-oh-filla-RYE-uh-sis)
is a serious and potentially fatal disease of dogs.
Long white worms, technically known as Dirofilaria immitis
(dir-oh-fill-AY-riah im-MIGHT-iss), are the cause. Adult
worms, which reach a length of 6 to 14 inches, live
in the right side of the heart in the adjacent large
blood vessels. A dog may have several hundred of them
in its system, although the number is usually much less.
Occasionally
canine heartworms are found in other animals such as
foxes, skunks, horses, and cats. In a few isolated instances
they have been reported in people as small disturbances
in the lungs, having little or no effect on the person's
health. Such cases are considered biological oddities.
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What
Does It Do?
Large
accumulations of adult worms impair circulation of the
blood, which can result in serious damage to a dog's
heart, lungs, liver, and kidneys. The important thing
for dog owners to remember is that a great deal of damage
can occur before any outward signs of heartworm disease
are noticed. Although a dog can lead a nearly normal,
healthy life with a few heartworms in its system, in
advanced stages the disease may cause its victim to
have difficulty breathing, cough, tire easily, become
listless, lose weight or faint. If not detected and
controlled with proper treatment, the disease can lead
to congestive heart failure and death.
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How
Does a Dog Get Heartworm?
Heartworm
infection is spread by mosquitoes. When a mosquito bites
an infected dog, it takes up blood which may contain
microscopic immature forms of heartworms called microfilariae.
The microfilariae incubate in the mosquito for about
two weeks, during which they become infective larvae.
Then, when the mosquito bites another dog, the infective
larvae are passed into the second dog, infecting it.
The infective larvae migrate through the tissues of
the body for about three months, then enter the heart
where they reach adult size in another three months.
The mosquito is the only natural agent of transmission
for canine heartworms. As you might expect, heartworm
infection is more common in areas where mosquitoes are
numerous, and outdoor dogs constantly exposed to mosquitoes
are the most frequent victims.
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How
Is It Detected?
The only
way to detect heartworm disease in its early states
in through a blood test. A veterinarian, using relatively
simple diagnostic procedures, can usually detect the
tiny heartworm microfilariae in an infected dog's blood.
But occasionally, an infected dog will have adult heartworms
but no microfilariae. In such cases an x-ray or echocardiogram as well as other laboratory tests may be needed to confirm heartworm
infection.
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Can
Infected Dogs Be Treated?
Most
dogs can be successfully treated for heartworms if the
disease is detected early. The adult worms are killed
with an arsenical drug given through a series
of carefully administered injections. A few days after
treatment, the worms die and are carried by the bloodstream
to the lungs where they may lodge in small blood vessels.
They then decompose and are absorbed by the body over
a period of several months. There is always some risk
involved in treating a dog with heartworms. However,
fatalities resulting from treatment are rare among dogs
that are otherwise in good general health. The patient
should be given a thorough physical and laboratory examination
prior to treatment, and any other problems that might
cause complications should be corrected before heartworm
treatment begins. Following treatment, complete rest
is needed to prevent lung damage from the dead and decomposed
worms. Excitement and exercise should be avoided for
a period of time, followed by gradual return to normal
activity. After all adult heartworms are eliminated,
another drug must be given to rid the bloodstream of
microfilariae, which are not affected by the drug used
to kill adult heartworms.
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Can
It Be Prevented?
The best way to prevent infection is to keep your dog healthy by minimizing drug and vaccine exposure, feeding a proper diet (fresh food in moderation and variety) and homeopathic care. Minimize mosquito bites by using topical essential oil sprays (or similar non-toxic products). In certain cases your veterinarian may recommend a low dose of a drug that keeps the infective larvae from
developing into adult worms. This drug should only be given during mosquito
season. It is actually not a preventative, but rather, early treatment of disease (remember it is always better to prevent disease than to have to treat it). When a dog takes this drug (usually Heartgard or Interceptor) any microfilariae that have been transmitted by a prior mosquito bite are killed (hence the monthly administration though there is good evidence that the so-called "throwback period" is actually 6-8 weeks).
Like most animal
health problems, canine heartworm disease still holds
mysteries that veterinarians and other scientists are
trying to solve. But adequate treatment and preventative
procedures have been developed, and the conscientious
dog owner, cooperating closely with his veterinarian,
can keep his pet free from this disease.
Heartworm disease is very preventable but potentially difficult and dangerous to treat. As always, prevention through holistic care is
the best answer.
Please note:
The information provided here is meant to supplement
that provided by your veterinarian. Nothing can replace
a complete history and physical examination performed
by your veterinarian. - Dr. Jeff
I greatly value your feedback. Please let me know what
you think of this site and what you would like to see
on it. drjeff@homevet.com
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Last modified
at 10:17 PM on 1/5/98.
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