Preventing heartworm in your dog is a year-round task. That’s because mosquitoes exist just about everywhere, even in regions that have long, cold winters. While mosquitoes are a nuisance to us, they pose the threat of heartworms to your dog. Before heading out with your dog for a game of fetch in your potentially mosquito-laden backyard, take a few minutes to learn about heartworms and see why prevention, and regular treatment, are essential.

What are heartworms?

Heartworms (Dirofilaria immitis) are actually a variety of roundworm. These worms mature into adults, mate and produce offspring—all while living inside your dog’s heart, lungs and associated blood vessels. Adult heartworms, which look like cooked spaghetti, can live inside your dog for many years; female heartworms can reach up to 12 inches in length.

The heartworm life cycle

Mosquitoes play a key role in the heartworm’s life cycle. Mosquitoes are the primary means of transporting the disease to dogs (as well as cats and other pets). In the United States, the warm southern regions have historically seen a larger occurrence of heartworms, but the disease has been reported in all 50 states.

Heartworms go through a long series of larval (immature) stages before becoming adults. The first larval stage exists in dogs that already have an infestation of adult heartworms. When an affected dog is bitten by a mosquito, it is possible for these first-stage larvae to migrate to the mosquito. Then they complete two more larval stages before migrating to the mouth of the mosquito, where they can be transferred via a mosquito bite to another dog. (Heartworm cannot be transmitted from dog to dog). Once there, the larvae can continue their progression to adulthood, where they infect areas in and around the dog’s heart and lungs. Breeding-age adult heartworms then produce a new set of first-stage larvae and the cycle begins again. Adult heartworms in dogs can lead to a wide range of health problems, and if left untreated, will almost always result in death.

Heartworm symptoms

It can be difficult to determine whether a dog has adult heartworms just by observation, although a persistent cough—particularly during exercise—is a classic sign, and a cough combined with lack of energy during exercise can potentially be indicative of a more severe case. Veterinary blood tests and other examinations are used to make a definite diagnosis.

It’s possible to cure a dog of an infestation of adult heartworms, but the process is time consuming, expensive and can be very hard on your dog. Treatment typically requires hospitalization while injections of heartworm adulticides are administered, along with several weeks of limited exercise. And this doesn’t even address the issue of previous damage to the dog’s body prior to treatment. You’ll need to work closely with your veterinarian to determine the best treatment options for your pet.

Prevention is key

When it comes to heartworm, prevention is key. Since it isn’t practical (or possible) to protect your dog from getting a mosquito bite, the best solution is to prevent potential heartworm larvae from completing their life cycle in your pet’s body. Prevention is simple and inexpensive. Monthly or semi-annual treatments of prescription oral pills (aimed at killing heartworms at the larval stages) are extremely successful in preventing heartworms from infecting your dog. Topical skin products are also available.

Don’t assume that your dog doesn’t need protection during the winter. Year-round protection helps guard against an accidental lapse in protection (forgetting to administer a pill for one month, for example). Many heartworm prevention products also provide protection against other parasites, making year-round protection essential.

Ask your veterinarian about the best preventative solution for your dog.

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