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Pet Health
Heartworm

What Is Heartworm?

Heartworm disease is a serious and potentially fatal condition caused by parasitic worms
living in the arteries of the lungs and occasionally in the right side of the heart of dogs,
cats and other species of mammals, including wolves, foxes, ferrets, sea lions and (in
rare instances) humans.

Dogs and cats of any age or breed are susceptible to infection

The worms travel through the bloodstream—harming arteries and vital organs as they go—
ultimately completing their journey to the vessels of the lung and the heart chamber about
six months after the initial infection. Several hundred worms can live in one dog for five to
seven years. Heartworm disease is serious, and can be fatal.

What Causes Heartworm?
Heartworms are transmitted from animal to animal by mosquitoes. The lifecycle of the
heartworm is complex. An animal must carry at least two heartworms (a male and a female)
in order for female heartworms to reproduce. Females produce babies, called "microfilariae,"
which are shed into an animal’s bloodstream but are not capable of directly causing
heartworm without first passing through a mosquito. The microfilariae must be taken up by
biting mosquitoes, and transform into infective larvae over a two-week period inside the
insect. When the mosquito next bites a susceptible animal, the infective larvae enter the
tissues and begin a migration into the blood vessels.

Heartworms enter an animal’s bloodstream as tiny, invisible larvae, but can reach lengths of
more than twelve inches at maturity.
What Are the General Symptoms of Heartworm?
Symptoms of heartworm infestation can include labored breathing, coughing, vomiting,
weight loss and listlessness, and fatigue after only moderate exercise. However, some dogs
exhibit no symptoms at all until late stages of infection.

How Is Heartworm Diagnosed?
Heartworm disease is diagnosed by examination, radiographs or ultrasound, and a
veterinarian-administered blood test. All dogs should be routinely screened with a blood test
for heartworm either annually in spring, at the start of mosquito season, or before being
placed on a new prescription for a heartworm preventive.

Which Dogs Are Prone to Heartworm?
Heartworm infestation can happen to any dog (as well as cats and some wild animals), but
since mosquitoes are their carriers, dogs who live in hot, humid regions—conditions in which
mosquitoes thrive—are at the greatest risk. The disease has been seen in every state except
Alaska, but is most common in or on the East Coast, southern United States and Mississippi
River Valley.

How Can Heartworm Be Prevented?
The good news is that heartworm is easy preventable with an inexpensive, chewable pill
available with a vet’s prescription. The pills—highly palatable to most dogs—are usually
administered monthly and manufactured by several companies. The pills can be given to dogs
under 6 months of age without a blood test, but older animals must be screened for the
disease prior to starting medication. You can opt to give your dog a pill only during mosquito
season (spring through first frost), but the most recent recommendation from the American
Heartworm Society is to keep giving them all year—not only does this avoid errors, but many
of the products also prevent other intestinal parasites. There are also topical products
available that you can apply to the skin.

How Is Heartworm Treated?
After diagnosis, a thorough examination of the infected dog should be conducted to evaluate
the best course of treatment and the potential risks involved. The most common course of
treatment is a series of injections of drugs called adulticides into the dogs’ muscle. This cure
has a high success rate and usually requires hospitalization; in certain circumstances,
however, it may be performed on an outpatient basis. However, all treatment protocols
require several weeks of exercise restriction after treatment and are not without risk.
Disease prevention is a much better and safer option. After treatment, your dog should be
placed on a preventative medication to reduce the risk of infection.

When Is It Time to See the Vet?
If you notice that your dog’s energy has decreased, she seems ill, or she’s exhibiting any of
the general symptoms described above, please contact your veterinarian immediately.

Need to find a qualified Veterinarian?  Go to  the  AAHA's online Hospital Locator
Heartworm disease prevention is easy. In most cases, a once monthly prescription treatment is
all that is needed to effectively protect your dog or cat from parasites. Save today on discount
Heartworm pet meds and medications including; Heartgard Plus, Interceptor, Sentinel,
Revolution and Iverhart Max.