How Do Dogs Get Heartworm?

Kate Barrington
by Kate Barrington
It’s a potentially deadly disease that can be prevented… but how do dogs get heartworm? Personally, it’ll be one more reason to hate those little blood suckers!

According to the American Heartworm Society (AHS), only about 55 percent of dogs in the United States are currently protected by a heartworm preventive – that leaves more than 27 million dogs at risk for contracting this deadly disease. Unfortunately, many pet owners do not realize the danger of heartworm and don’t even understand the way a dog can become infected. So how do dogs get heartworm? Take the time to learn the basics about heartworm – including the ways dogs can become infected – and you will take the necessary steps to protect your pet.

Related: 5 Heartworm Facts You Need To Know

How Do Dogs Get Heartworm?

There is only one way a dog can become infected with heartworm – if it is bitten by an infected mosquito. The process through which a mosquito becomes infected, however, is a little bit more complicated. First, the mosquito must bite a dog that is already infected with adult heartworms that have begun reproducing. In order to produce heartworms, the dog must be infected with at least one male and one female heartworm. A dog can be infected with up to 250 heartworms at a time, so where there is one heartworm there are typically multiple.

Related: Naturally Safe Mosquito Repellent For Dogs

When the mosquito bites the infected dog and sucks its blood, it takes into its own body some of the heartworm babies – called microfilariae. Once these microfilariae are inside the mosquito, they develop into larvae over a period of 10 to 14 days at which point they become infective. Then, when the mosquito bites another dog it transfers some of those infective larvae into the dog’s bloodstream. A dog does not immediately become infected with heartworm the moment it is bit by an infected mosquito – it isn’t until the larvae develop into adult heartworms and begin reproducing that the dog will actually test positive for heartworm. It generally takes about 6 months for the infective heartworm larvae to travel through the dog’s bloodstream to the heart and lungs where they begin to reproduce. Because it takes so long for the larvae to develop, dogs typically do not show any symptoms of heartworm until the adults begin reproducing.

How to Protect Your Dog

Nearly 100 percent of dogs that are exposed to the infective larvae of heartworms become infected with the disease. Once infected, the expected lifespan of the dog drops severely to an average of five to seven years. The heartworm disease is incredibly dangerous and deadly, but it is also easy to prevent. Giving your dog a monthly heartworm preventive takes only a few seconds but it could provide your dog with a full 30 days of protection. In order to start your dog on a heartworm preventive program, however, you must first have him tested for the disease. Puppies under six months of age can be started on a preventive without being tested because it takes the disease six months to develop, but they should be tested within another 6 months after starting the preventive.

The mosquitoes known to carry the heartworm disease can be found in all 50 states during any time of year, so your dog’s risk for contracting heartworm is ever-present. Because preventing heartworm is so easy, however, there is no reason for you not to do it. The cost of preventing heartworm is significantly lower than the cost of treating it and it will save your dog a great deal of pain and suffering if he never contracts the disease to begin with. If you haven’t already started your dog on a heartworm preventive program, talk to your veterinarian as soon as possible.

Kate Barrington
Kate Barrington

Kate Barrington is the loving owner of two cats (Bagel and Munchkin) and a noisy herd of guinea pigs. Having grown up with golden retrievers, Kate has a great deal of experience with dogs but labels herself a lover of all pets. Having received a Bachelor's degree in English, Kate has combined her love for pets and her passion for writing to create her own freelance writing business, specializing in the pet niche.

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