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How Do Dogs Get Heartworms And What You Can Do About It

Sad dog with heartworms at the vet Go find yourself a measuring tape. Seriously, go get it. Now, measure out 13 inches. That’s how long a heartworm in your dog can be.

And, it is not uncommon for up to 30 of them to be huddled together in and around the heart of your infected dog.

Yes, heartworms are dangerous. Here’s what you need to know about them and tips on how to deal with this parasite that’s endemic to, pretty much, the entire USA.

What are the Signs of Heartworm Infection?

Here’s the problem: newly infected dogs typically do not exhibit any signs

It takes six months before the infection can even be detected using current methods. As the worm burden increases — this can take years — signs begin to appear.

For example:

  • Mild but persistent cough
  • Lethargy
  • Signs of fatigue with little exercise
  • A lack of appetite
  • Loss of weight.

As symptoms progress, the dog may experience difficulty breathing; ultimately, there could be a sudden collapse with death within a week.

But How Do Dogs Get Heartworms?

Dogs get infected through mosquitoes. But, it’s a bit of an extended process. First, the mosquito bites an already infected animal — this could be a wild animal.

Larvae from the infected animal enter the mosquito along with the blood meal. Heartworm larvae, for some reason, require living within a mosquito to reach the stage that make it dangerous to dogs … and it takes about two weeks for that to happen.

When that mosquito bites your dog, some of those infective larvae make it into his bloodstream. It takes a further six months for these larvae to grow into adult worms. Worms can live in a dog for 5 to 7 years.

Why Should I Take Preventative Action

If you don’t take preventative measures here is what’s in store of you:


Heartworms cause permanent damage to the heart and lungs

Because their presence reduces the efficiency of the right side of the heart, the heart attempts to compensate by growing in size. Trouble is that only makes matters worse.


Treatment to eliminate heartworm is High Risk for dogs

It requires strict cage rest for several months while the body deals with the dying worms — vigorous exercise can, literally, result in sudden death.


Recommended treatment for heartworm is frightfully expensive

Treatment can cost you hundreds of dollars. It’s not uncommon to spend over $1000.

On the other hand, the yearly cost of prevention is around $50, varying a little with the weight of the dog.

Currently, the American Heartworm Society recommends year-round preventative treatment.

What Can I Do to Prevent Heartworms

Clearly, preventing bites by mosquitoes will prevent infection. Equally clearly, that is pretty much impossible to accomplish.

Instead, there are simple monthly medications — chewables or topicals — that will kill larvae before they can become adult heartworms.

There is also a once-in-6-month injection that can be employed. Such medication has the added benefit of protecting your pet from other parasites like roundworms, hookworms, mites, fleas and ticks.

Products containing

  • Ivermectin (injectable or chewable)
  • Milbemycin (chewable)
  • Selamectin (topical)
  • Moxidectin (topical) can be used.

Caution: Ivermectin can be deadly to some dogs of certain breeds like Collies, Sighthounds and others; it should be administered by a licensed veterinarian.

What if My Dog is Already Infected with Worms

There are two ways to treat your pet.

Method #1 – Fastest (Recommended)

The recommended method of killing adult heartworms involves the use of a product containing melarsomine. The American Heartworm Society recommends a single injection followed, in about a month, by two additional injections 24 hours apart.

In addition, treatment for a bacteria found in heartworm is required — azithromycin, doxycycline or rifampin works. During this treatment, it is extremely important that your dog be provided strict cage rest; exercise can kill him. Larvae will be killed by preventative treatment.

Method #2 – Slower

The second method is to employ the relatively passive method of using preventatives (mentioned above). These will kill the larvae quickly; however, adults can take up to two years to die.

The American Heartworm Society does *not* recommend this method because of the additional damage those heartworms will cause to your pet during those two years.

A Final Word

Heartworm is a dangerous parasite that is considered endemic to the US. The American Heartworm Society recommends preventative treatment all year round. Here is a disease that is eminently appropriate for the proverb, “prevention is better than cure”.