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Have You Given Your Dog Heartworm Prevention This Month?

By: Sarah Hilario, DVM


Heartworm disease is very common in Florida due to our warm weather.  As pet owners, we should all be familiar with this disease, as the consequences of this condition can be fatal without proper treatment.  In this article I will discuss one of the most misunderstood treatments of heartworm disease, the so called “slow-kill” method of treatment.  But first, what is heartworm disease?  The scientific name of the responsible parasite is Dirofilaria immitis and it is spread by mosquitoes.  It is not contagious between dogs; it is only passed by the bite of a mosquito.  It takes 6 months from the time a mosquito bites a dog for the worm to develop into an adult and travel from the skin into the heart and lungs.  At this point, a simple blood test can be performed by your veterinarian to determine if your dog has heartworm disease.   However, if a dog is tested before 6 months have passed since the mosquito bite, the test will be negative even though the dog is infected.  A positive test result is distressing news, but thankfully there are treatment options.

The American Heartworm Society recommends treatment with a drug called Melarsomine to kill adult heartworms.  This drug is given intramuscularly two to three times over a month’s period and kills greater than 95% of the worms.  This is the only FDA approved treatment option for heartworm disease.  However, there is an alternative method of treatment meant for dogs with specific conditions that prevent them from receiving Melarsomine injections safely.  This technique has become known as the “slow-kill” method, but contrary to its name, it does not kill heartworms.  Typically, a heartworm prevention containing Ivermectin such as Heartgard is used monthly in this alternative treatment plan.  This medication will prevent the pet from obtaining new infections from mosquito bites and may even help shorten the lifespan of adult worms.  Unfortunately, it may take years before the worms finally die a natural death and during this time they could permanently damage the structures of both the heart and lungs.  Also, during these years the dog must be exercise restricted to help prevent a severe side effect of dying heartworms, pulmonary thromboembolism, a condition in which a dead heartworm blocks blood flow to the lungs.

If you are faced with a positive heartworm test, consult with your veterinarian about the different treatment options before deciding which will be the best for your dog.  Even though treatment of heartworm disease usually has a positive outcome, it is still much safer and less expensive to prevent heartworm disease in the first place by giving monthly heartworm prevention year round.  So, did you give your dog its heartworm prevention this month?