Heartworm Disease in Dogs

General Information

The life cycle of the heartworm begins when an infected dog, carrying tiny immature heartworms (microfilariae) circulating in its blood, is bitten by a mosquito. The mosquito takes in microfilariae (larvae) when it feeds.

During the next two-three weeks, the larvae develop within the mosquito into the infective stage.

When the mosquito feeds again, it can
transmit infective larvae to the healthy dog. The larvae penetrate the dog's skin and migrate through the tissues and develop over the next few months, eventually reaching the dog's heart.

Once in the dog's heart, the worms can grow to as long as 14 inches and cause significant damage to the heart, lungs and other vital organs. If left untreated, heartworm disease can result in death.

Heartworm FAQs

Can my dog get heartworm disease?
Yes. Your dog can get heartworm disease, whether he's an "outside" dog or even if he stays inside most of the time. Dogs get heartworm disease from mosquitoes. It is the female mosquito that bites and transmits the infection. Female mosquitoes are very tiny and can easily slip through cracks around windows, doors or screens. Every dog can be at risk, indoors or out.

Are some dogs more susceptible than others?
Unfortunately, no dog, or breed of dog, is immune to heartworm disease. The mosquito that bites your dog could be carrying this common and deadly parasite. One bite from an infected mosquito is all it takes for your dog to become infected.

How can I know for sure if my dog already has heartworm?
The only way to know for sure is to have your family veterinarian examine and test your dog. The procedure is quick and easy. But don't delay in calling your veterinarian to arrange for a heartworm test. If your dog gets heartworm disease, treatment can be dangerous for him and expensive for you.

When is the right time to get my dog tested?
Mosquitoes, the carriers of heartworm disease, can be found at varying times of the year depending on the climate. Ask your veterinarian when the best time is to have your dog tested.

How can I prevent my dog from getting heartworm disease in the future?
If your veterinarian determines that your dog is free of heartworms, he or she will tell you how easy and convenient prevention can be. It's important to follow your veterinarian's instructions; if you don't, your dog could still be at risk. Remember, the first, most important step is to have your dog tested for heartworms.

Heartworm and Traveling with Your Dog

Dog owners, be aware of the following:
Alex, a Labrador retriever, lives in a heartworm-endemic state. He has heartworms, but his owners don't know it because the disease is not easily detected until its later stages. Alex travels with his owners on vacation to states where there are fewer incidences of heartworm disease like Alaska. While in Alaska, Alex is bitten by a mosquito, which picks up the heartworm larvae from his bloodstream. Later, the same mosquito bites a healthy local dog, infecting him with heartworm. The cycle continues.

A problem can also result if a dog from a low-incidence state like Alaska travels into a state where heartworm disease thrives, is bitten by a mosquito and then brings the disease back home.

What Does This Mean For All Dog Owners?
Now that greater numbers of people are traveling across the country with their dogs, on vacation or visiting friends and relatives, no state is entirely heartworm-free. Heartworm disease continues to pose a threat to dogs across the United States. Because heartworm disease is potentially fatal, owners should visit their family veterinarian to learn how easy and convenient prevention can be.

When Traveling, Help Protect Your Dog from Heartworm Disease

1. Many states require that owners traveling with their dogs obtain an up-to-date health certificate from a licensed veterinarian.
2. As a part of the examination, your veterinarian may check for heartworm disease. If your dog is not infected, the veterinarian can recommend preventive measures. Prevention is the key to protecting a dog both at home and away.
3. Upon returning home from a trip, owners should revisit their family veterinarian for an examination to make sure their dog did not pick up any parasites, either internal (e.g., heartworm, hookworm, roundworm) or external (fleas and ticks).
4. Remember, annual heartworm tests are important whether or not your dog is traveling.