Heartworm in dogs – how to keep your dog safe

Almost every dog owner has heard about heartworm in dogs. If you haven’t, don’t worry—you’re in the right place! ☺️

Heartworm is a serious disease caused by an internal blood parasite called Dirofilaria immitis. It’s widespread and, in my opinion, often underestimated. The treatment is lengthy and can be potentially fatal, but the good news is that it’s preventable.

Many people know that dogs can get heartworm. However, in my experience, it’s more of an “I’ve heard of it” rather than an “I need to protect my dog” mindset. This isn’t the best approach when dealing with a preventable, life-threatening disease that’s endemic in many areas 😟

I also believe it’s every veterinarian’s responsibility to educate their clients about the risks, especially during the summer travel season.

Since you’re here on my blog, I’ve got a complete guide for you 🤗

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This post may contain affiliate links, which means I may receive a commission, at no extra cost to you, if you make a purchase through a link. Please see my full disclosure for further information.

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While I am a veterinarian, this article is not intended to replace professional veterinary advice. If you have any medical concerns about your pet, consult your vet immediately. Always seek professional assistance if you are unsure of your pet’s health.

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How do dogs get heartworm

In my previous posts, I talked about diseases transmitted by ticks. Some people mistakenly think ticks also carry dirofilariasis, but that’s not true.

Heartworm is actually transmitted by mosquitoes, which carry heartworm larvae from one host (like a dog, cat, or ferret) to another.

Here’s how it works: A mosquito bites an infected host and ingests the first stage of heartworm—microfilariae. These then develop into infectious larvae inside the mosquito. When the mosquito bites your pet, it injects these larvae into their bloodstream.

The larvae continue to develop in your dog’s tissue over about two months. Once mature enough, they leave the tissue as developing adults and travel through your dog’s bloodstream to the blood vessels around the heart and lungs. In advanced infections, they can even move directly into the heart.

It takes another 5-7 months for these larvae to turn into mature adults capable of producing microfilariae. These adult parasites lodge in the blood vessels around the heart and lungs and can live up to 7 years.

When another mosquito bites your dog, it ingests the microfilariae from your dog’s blood, starting the cycle all over again.

So, mosquitoes are the key players here—they carry the larvae from one animal host to another. Without them, the whole cycle wouldn’t be possible. One infected animal can’t directly infect another animal or a human. The spread of heartworm is directly linked to mosquito activity.

Several studies have shown that heartworm incidence in dogs is rising (see references at the bottom for more info 🙂). Climate change and invasive mosquito species are major factors driving the spread of heartworm infections.

Today, heartworm is endemic in many areas, including Canada, several U.S. states, Europe, and southeastern Asia.

Remember, heartworm is a parasitic disease that needs mosquitoes to spread, so you can’t catch it from your dog.

However, there are a few other diseases you can get from a dog.

Here’s an infographic to help you understand it better:

Symptoms of heartworm in dogs

Heartworms that are lodged in blood vessels and the heart cause irritation and inflammation. Your dog’s immune system may cause further damage, especially in response to dead worms. The constant irritation can lead to scarring and reduced flexibility of blood vessels.

Many dogs show no or just a few mild symptoms in the early stages of the disease. However, the longer the infection persists, the more severe the signs will get.

Symptoms of heartworm in dogs may include:

• coughing (mild or persistent)
• reluctance to exercise
• decreased appetite
• fatigue
• fainting
• labored breathing
• blue discoloration of the gums
• accumulation of fluid in the abdominal cavity

Additionally, blood clots, dead worms, or a large number of worms can block blood vessels and/or the heart, which can lead to a cardiovascular collapse. This condition is called caval syndrome.

Caval syndrome is a medical emergency. At this stage, the dog needs immediate surgical intervention, or he will most likely die.

Diagnosis of heartworm in dogs

Heartworm is a progressive disease, meaning the sooner we catch it, the better the prognosis.

There are a few options for diagnosing heartworm in dogs. The most specific and widely used is an antigen detection test. It’s easy to perform and reliable.

However, this test can’t detect the very early stages of the infection. That’s why your vet may recommend regular yearly testing.

If a dog tests positive, further diagnostic tests are needed to confirm the diagnosis.

Treatment of heartworm in dogs

The treatment for heartworm depends on several factors, including your pet’s medical history, existing health conditions, the severity of the infection, and the extent of heart and blood vessel damage.

The goal is to stabilize your pet and kill the adult and immature parasites. Before starting heartworm treatment, your vet may prescribe medications to stabilize the heart and lungs.

There are specific approved protocols and guidelines for treating heartworm in dogs.

Dead worms can cause severe respiratory problems. Signs include coughing, spitting up blood, labored or rapid breathing, lethargy, lack of appetite, and fever.

Patients with these symptoms need cage confinement, several days of oxygen treatment, and medications to control inflammation and reduce blood clotting.

You can reduce the risk of post-treatment complications by confining your dog or restricting their activity during treatment and for 4-6 weeks afterward. I know it’s tough, but it’s necessary 😔

In some cases, there are so many heartworms in a dog’s heart that they need to be removed surgically.

To summarize, the treatment of heartworm in dogs consists of:

• stabilizing the patient
• actual heartworm treatment with an approved protocol
• activity restriction or confinement
• surgery (in extreme cases)

Your dog needs to be tested again 9 months after the treatment to confirm that all parasites have been killed and eliminated. I would recommend testing your dog every year.

Heartworm prevention for dogs

As I mentioned earlier, heartworm disease is preventable, and there are several approved drugs that can be used safely.

Most preventive products need to be given monthly, so it’s a good idea to set a reminder in your calendar. The most common mistake pet owners make is forgetting to administer the medication or using expired products.

It’s best to start preventive care as early as the product label allows, especially if you live in an area where heartworm is endemic. Puppies are just as susceptible to heartworm as adult dogs.

Preventive products are usually dosed according to body weight, so there’s no need to worry about overdosing your furry friend. Talk to your vet about the best preventive care for your puppy.

Products you can use to protect your dog:

As you know, it’s important to regularly deworm your dog, not just for their health but also for your own protection.

We live in such an awesome age that you can now buy products that kill the most common intestinal parasites and protect your pup against fleas, ticks, and heartworms 😎

There are several products on the market you can choose from, for example,