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Dear Daisy Dog

My dog was diagnosed with heartworms. My veterinarian recommends that I give her the preventive tablet for several months before he administers injections to kill the heartworms.

Is it safe to give the preventive when she already has heartworms? Why is he waiting so long to treat her heartworms?

Daisy Responds

Your veterinarian’s treatment plan is consistent with the recommendations of the American Heartworm Society, the authority on heartworm prevention and treatment.

I don’t have firsthand experience with heartworms, because I take the preventive medication throughout the year. But I know from a dog friend who had heartworms that they live in the blood and damage the blood vessels, heart, lungs and other organs.

Damage to these organs leads to exercise intolerance, cough, difficulty breathing and other problems.

Furthermore, your dog’s heartworms can spread to other pets through mosquito bites, so it’s important to treat them.

The first step is to kill the immature heartworms, or larvae. The monthly preventive medication does that.
It also kills microfilaria, the babies produced by mature heartworms. Microfilaria spread the infection to other pets when a mosquito ingests them during a blood meal.

Killing most of the larvae and microfilaria first is easier on your dog’s body than killing them — plus the adult heartworms — with the injections.

You see, as the larvae, microfilaria and adult heartworms die and disintegrate, their bodies may partially block the blood vessels to the lungs.

The most common signs of this problem, called pulmonary thromboembolism, are a cough (including coughing up blood) and fever.

The risk can be minimized by restricting your dog’s exercise during and after treatment — and employing your veterinarian’s multi-step treatment protocol.

Follow his recommendations, and your dog should do well. To avoid infections in the future, give her the monthly preventive throughout the year.

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