Sunday, April 5, 2015

WHAT YOU NEED TO KNOW ABOUT HEARTWORM


Spring is officially here and with it, mosquitoes have begun their emergence.  Besides being terribly annoying, mosquitoes can carry the nematode parasite known as Dirofilaria immitis, which causes that deadly disease known as heartworm.  In companion animals, heartworm is diagnosed mainly in dogs and less frequently in cats and ferrets.  However, heartworms also live in other wild animal hosts such as wolves, coyotes, foxes, California gray seals, sea lions, and raccoons.  Make no mistake, even though the disease is easily preventable, it is prevalent, and it is a killer.

Mosquitoes acquire the parasite while feeding on an infected host.  Once ingested by the mosquito, the parasite develops into mature infective larvae.  These larvae then migrate to the “mouthpart” of the mosquito so that when it bites, they move into the wound created and deposit themselves into the bloodstream where they will then begin the harmful portion of their life cycle.  Heartworm is only conveyed through the bite of an infected mosquito, therefore an infected dog cannot transmit the disease to either people or other pets. 

It will take these deposited larvae approximately 6 months to mature into adult heartworms.  If untreated, these adults will mate and produce progeny, thus increasing their numbers.  In addition, adult heartworms can live for 5 - 7 years in dogs, thus each mosquito season can potentially increase the number of worms in an already infected pet.

As these heartworms move through the body they can cause extensive damage to many vital organs such as liver, lungs, kidneys, and heart.  They can cause inflammation of the blood vessels, and too many of them can cause heart failure, resulting in the pet’s death.  However, by giving a relatively inexpensive monthly oral medication, heartworm in dogs is preventable.  One may wish to give the dog the chewable pill only during the typical mosquito season.  However, because many of these preventatives also include a control for roundworms, whipworms, or tapeworms, it is best to give it throughout the year.  When initially choosing a method of prevention, discuss it with your veterinarian.  They can make recommendations based on your pet's requirements.

One of the first symptoms that the animal has heartworm is coughing.  Coughing up bloody mucous and chest pain follow.  Other symptoms are vomiting, weight loss, fatigue, and difficulty breathing.  Some dogs may not have any symptoms until the infection is in its late stages.  Even though they may have a large number of worms present, symptoms may not be observed in inactive dogs until a dramatic increase in activity causes symptoms to manifest.

The best way to treat heartworms is, initially, to have x-rays and blood tests done to establish how serious the infection is.  After this, a series of injections of drugs called adulticides is administered to the dog.  The two adulticides used most commonly are derivatives of arsenic.  Depending on whether all the pre-treatment tests are done, or just the treatment given, costs can range anywhere between a few hundred dollars to over a thousand.  However, if you opt instead to use the common monthly preventative in a dog with the disease, you can expect the dog to remain heartworm positive for about two years.  Unfortunately, while being treated the heartworms continue to cause permanent damage to the heart.  Nevertheless, if someone cannot afford the actual treatment, using the monthly preventative is certainly better than not doing anything.

It is also important to remember that during and after treatment, for several months the dog must remain quiet.  After the worms begin to die, they break into pieces that may cause blockage of vital blood vessels, which could also result in death.  Keeping the dog quiet allows his/her body time to absorb the dying worms.

If you are interested in learning more, The American Heartworm Society (https://www.heartwormsociety.org/pet-owner-resources) provides information and resources available for pet owners. 


Our pets depend on us to take care of them.  Heartworm prevention is one of the ways we can protect our faithful companions from disease and help insure that they will have long, active lives and healthy hearts.

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