Heartworm Prevention

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Heartworm Disease – An Update

Prevention is your dog's best bet against heartworm disease.

 April is the time of the year when veterinarians start to check dogs for exposure to heartworm disease and start heartworm prevention that they may have been infected with during the previous mosquito season.

If mosquitoes are biting you, chances are they're biting your pet too and one mosquito bite can cause the parasite to enter a pet’s body and mature into long worms that live in the heart and major vessels surrounding the heart. Once there, the worms grow, feeding off the lining of the heart and plugging essential blood vessels.  Untreated, the disease leads to significant and deadly damage to the pet’s heart, lungs, kidneys and liver. Clinical signs seen in dogs include cough, difficulty breathing, weight loss, exerciseintolerance, and eventually heart failure and death.

Unlike intestinal parasites, which can be easily treated, treating a heartworm infestation is very expensive, sometimes difficult and dangerous. It is far easier and more effective to prevent the problem in the first place. In theory, the best way to prevent heartworms is to keep your dog from being bitten by a mosquito. Unfortunately, preventing mosquito bites can never be 100 percent effective. 

A prevention program should be started at 6 to 8 weeks of age in endemic areas, or as soon thereafter as climate conditions dictate. In the Deep South, where mosquitoes are a year-round problem, dogs should be kept on preventive drugs all year long. In areas where it is not necessary to administer the drug year round, start one month before the mosquito season and continue one month beyond the first frost (generally from May or June to November or December).

If your dog is not taking preventive medicine and is six months or older, he may already be infected with reproducing adult heartworms. Your veterinarian needs to use a blood test to confirm that your pet is heartworm-free before your dog can start taking the medication.

Why? If an infected dog takes heartworm prevention he runs the risk of an anaphylactic-shock reaction because the treatment involves a sudden killing of microfilaria, or baby heartworms, present in the bloodstream.