University of Florida

Preventing Heartworm Disease

From chikungunya to malaria to West Nile, many of us are familiar with the diseases mosquitoes can give to humans. However, mosquitoes can also transmit disease to pets. Dog heartworm disease, which can be life-threatening and disabling, has been diagnosed in pets from Alaska to Florida. 

Fortunately, for you and your furry friend, heartworm disease is preventable.

How It Works

Heartworm disease begins to spread when a mosquito bites an infected animal. The worms are transferred to the mosquito and then complete their lifecycle inside the mosquito. When they’re done, the worms move to the mosquito’s mouth. The next time the mosquito bites an uninfected dog, the worms are passed along.

After the mosquito bites the dog, the infective larvae burrow into the dog’s skin near the bite and stay there. It’s not until 70–90 days after the dog has been bitten that the young worms move and reach the dog’s heart.

The worms continue to grow and mate, sending the larvae throughout the blood. This is when the disease can be diagnosed in the dog; however, the dog may not show symptoms until one year after it’s infected. The worms infect the animal’s heart, lungs, and blood vessels, which can lead to heart failure, lung disease, and circulatory problems.

Preventing Heartworm Disease

Prevention is the most important factor in protecting your dog against heartworm disease. Visit your veterinarian to get a prescription for monthly heartworm mediation for your pet. If your dog is already infected with heartworms, then your dog needs to undergo treatment, which is often expensive and risky.

If you forget to give your pet its heartworm preventative, then be sure to test the animal for heartworm disease during its next vet visit.

Signs of Heartworm Disease

While some dogs may not show any symptoms until the disease has progressed, be sure to look out for the following signs:

  • Easily tired
  • Insistent cough (may cough up blood and worms)
  • Weight loss
  • Reduced appetite
  • Extra fluid in the stomach, causing an enlarged belly
Adapted and excerpted from:

Mosquito-Borne Diseases,” American Mosquito Control Association (Accessed 10/2014).

J. K. Nayar and C. R. Connelly, “Mosquito-Borne Dog Heartworm Disease” (ENY-628), UF/IFAS Entomology and Nematology Department (07/2011).

Prevent Heartworms in Pets Year-Round,” US Food and Drug Administration (10/2013).


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