How Do Dogs Get Heartworms and More

Heartworm medication is perhaps one of the most common medicine prescribed to dogs at their check ups. Following their initial shots and boosters, heartworm prevention medicine is a huge piece of the puzzle in maintaining your dogs health. But how do dogs get heartworm, what are the symptoms and how can it be treated should they receive them? We’re answering all of that this time on the Acoma Animal Clinic blog!

How Do Dogs Get Heartworms?

I know the big question is how dogs get them, but first, let’s take a look at what heartworms are to better understand the entire process.

What are Heartworms

Heartworms, also known as Dirofilaria immitis, are parasitic roundworms. They are spread through mosquitos bits and while their traditional host is the dog, they can also infect coyotes, wolves, jackals, foxes, cats, and even humans, though this is very rare.

The Circle of Life

The life cycle of a heartworm begins when adult worms mate and produce the larvae. The larvae are then released into the blood of the host animal. A mosquito will feed on the infected animal and ingest some of the larvae. While instead the mosquito, the heartworm larvae will progress through a couple of states, from L1 to L3. When the mosquito feeds on another healthy dog, it unknowingly transmits the larvae to the dog, typically in the tissues just beneath the skin. There the larvae will mature in the muscles and blood vessels until they are ready to infest the heart and pulmonary artery. There they will mate and create new larvae, the cycle beginning again.

You may have noticed, we just answered how dogs get heartworms, but let’s mentioned it again, big and bold:

How do dogs get heartworms? Through bites from infected mosquitos!

Signs and Symptoms of Heartworms

During the first six months of the infection, while the worms are still maturing, it is likely that the dog will show no signs. Early signs of infection include a cough, especially during or after activity. If the infection has advanced the signs of a severe infection include weight loss, coughing up blood, fainting, and congestive heart failure. Many dogs show no or little signs of infection so it’s important to stay vigilant, either with their prescription medicine or vet appointments.


If your dog has heartworms, don’t fret! Treatment is available! But before you can begin any treatment, your vet must first examine your pet’s heart, kidney, and liver function. So long as they are functioning correctly, your vet will recommend a course of treatment. The prescription typically prescribed can be tough on the body and if any of their organs aren’t functioning correctly it may make their symptoms and status worse. Once they have undergone treatment, your dog must rest, and be limited in their activity for a number of weeks to allow the dead worms to be safely absorbed into their bodies. If the dog exerts itself, there is the potential for the dead worms to beak loose and apart and travel into the lungs, putting them at risk for respiratory failure.


An ounce of prevention is worth a pound of cure as the saying goes. The most popularly recommended drug is ivermectin, sold under the brand name Heartgard (as well as others). These are usually administered in chewables or pill form and when done correctly and regularly they are over 99% effective in preventing heartworm infections. You can layer on top a mosquito preventative as well to ensure that should any mosquito attempt to feed on your dog they don’t live long enough to transmit the parasite.

Well there you have it! We’ve answered how dogs get heartworms, the signs and symptoms, treatment and prevention. With all this knowledge tucked under your belt, make an appointment with your vet today and get your pet’s health taken care of! If you’re in the Tucson area and need a vet, give us a call at Acoma Animal Clinic. We’ll see you next time!

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