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Heartworm Disease In Dogs: Everything You Need To Know

Written by: Molly Weinfurter
Molly Weinfurter is a writer for iHeartDogs, and she’s passionate about helping animals in need. She volunteers for Bailing Out Benji and a local dog rescue.Read more
| Published on January 16, 2024
iHeartDogs is reader-supported. When you buy via links on our site, we may earn an affiliate commission at no extra cost to you.

Every dog parent knows about the existence of heartworm disease since vets recommend yearly testing and monthly preventatives. However, not everyone knows the details of this condition. The reason dogs need constant preventatives is because heartworm disease can be life-threatening, so it’s always better to be safe than sorry with your furry friend’s health. Keep reading to find out what heartworm disease is, how it’s treated, and ways you can prevent it in your furry friends.

What is Heartworm Disease in Dogs?

Heartworm disease is when worms live inside your dog’s heart, lungs, and blood vessels. Dogs get these worms after getting bit by an infected mosquito, and the worms can mature and mate inside your dog’s body. If untreated, the worms will continue to reproduce, causing severe damage to your dog’s internal organs.

The heartworms inside your dog’s body look like noodles, reaching 4 to 12 inches long. They can live inside a dog for five to seven years if not treated, causing severe damage in the process. Once a dog is bitten by a mosquito and infected with heartworms, it can take up to six months for them to start testing positive. Heartworm disease cannot be passed between dogs because it can only be transmitted through mosquitos.

Microflaria heartworm

What are the First Signs of Heartworms in Dogs?

Heartworm symptoms in dogs can be hard to spot at first. Yet, the longer the worms are in your dog’s body, the more serious the symptoms become. If you notice your dog acting out of the ordinary, visit your vet as soon as possible.

Here are some common heartworm symptoms:

  • Coughing
  • Reluctance to exercise
  • Getting tired quickly
  • Trouble breathing
  • Decreased appetite
  • Weight loss
  • Swollen belly

These symptoms are usually divided up into stages. Stage one consists of no symptoms or a slight cough. Stage two usually includes more consistent coughing and lethargy. Stage three is when the symptoms become obvious. Your dog may appear sickly, get tired easily, or have trouble breathing. Stage four occurs when there are so many worms that they could block the blood flow (known as caval syndrome). Surgery is often the best course of action at stage four, but your vet can advise the best steps to save your dog’s life.

Heartworm could lead to heart failure or other life-threatening conditions. So, if you notice unusual behaviors in your dog, don’t take them lightly. It’s always best to be overly cautious with your furry friend’s health.

Can a Dog Recover from Heartworm Disease?

Yes, dogs can recover from heartworm disease with proper treatment. After treatment, the dog will no longer have heartworms in their body and can go on to live a normal, healthy life. However, treatment is long, and it’s most effective if heartworm is spotted early. That’s why it’s essential to get your dog tested for heartworm every year and give them heartworm preventatives as directed.

Dog at the vet

Treating Heartworm in Dogs

Every year, you will need to get your dog tested for heartworm at the vet before you can buy more heartworm preventatives. Even if you’ve given your dog their preventative on time every month, a heartworm blood test is still needed just to be safe.

A positive heartworm test means that your dog has adult heartworms. Left untreated, he will progress to heart failure and die, spreading heartworm larvae to every mosquito that bites him along the way, potentially infecting other unprotected dogs,” says Dr. Kathryn Primm.

If your dog tests positive, the vet will run another test to verify the results before moving forward with treatment. Unfortunately, heartworm-positive dogs must avoid intense exercise or any activities that will increase their heart rate. That means even the most playful pups must avoid running and jumping during treatment.

Most dogs will need to have restricted exercise for at least 2-3 months. During that period, a vet will administer Immiticide (melarsomine) in the form of an injection. Some dogs may also need to take medication at home during their treatment, which is usually doxycycline to avoid potential infection. Your vet will be able to give you the most accurate treatment timeline based on your dog’s needs and the severity of their heartworms.

Several months after the final injection, your vet will test your dog again to make sure the treatment has effectively removed the heartworms from your dog’s body.

Dog relaxing heartworm treatment

Can’t Heartworm Preventatives Treat Heartworm Disease?

It’s a common misconception that heartworm preventatives can treat heartworm disease. Some dog parents believe that they can just keep giving monthly preventatives to cause the heartworms to disappear. This isn’t the case. Hence the name: they’re only for preventing the disease, not treating it.

The monthly pills can precede the Immiticide injection and are a part of the approved protocol, but when used alone they are not effective. It can take up to seven years for a worm only treated with monthly product to die. Can you imagine the damage that worm can wreak on your dog’s heart and lungs in such a long time?” Dr. Primm says.

Even though heartworm treatment can be expensive, it’s worth it knowing it can save your dog’s life. Always follow your vet’s advice for a heartworm-positive dog.

Heartworm Prevention for Dogs

Heartworm preventatives are crucial for avoiding heartworm disease. They can be given as oral, topical, or injectable products, but oral preventatives are the most common. Talk to your vet about which product is recommended for your dog.

“Heartworm Preventive medication stops infection by killing the worms before they mature, reproduce, and cause damage. There is no drug that can stop the mosquito from carrying the larvae to your dog, so we have to stop them before they become damaging adults and make the infection worse with their offspring,” says Dr. Primm.

Preventative heartworm products can only be purchased with a prescription from your veterinarian. Every year, your vet will require your dog to get a heartworm blood test, and after the test, they will allow you to buy up to a year’s supply of heartworm preventatives. The test is necessary to make sure your dog doesn’t have heartworm. As mentioned earlier, even if you’ve been giving your dog their preventative every month, it’s still better to be safe than sorry by doing a yearly heartworm test.

Dog taking heartworm preventative

Best Heartworm Medicine for Dogs

Even though dog heartworm medicine requires a vet’s prescription, there are lots of products to choose from. Below are some vet-recommended heartworm preventatives to consider, but it’s always a good idea to talk to your vet about the best option for your dog.

These products can be purchased directly from your vet or from Chewy with a prescription. With Chewy, you can set up Autoship so your pup’s medications always arrive on time.

  • Chewable beef-flavored preventatives
  • Perfect for dogs that hate taking regular pills
  • Prevents and kill heartworms, roundworms, and hookworms

Heartguard is one of the most popular preventatives for dogs because it comes in a chewable tablet with beef flavor. So, it’s easy to administer to pups that normally hate taking pills because it smells and tastes like a treat. It prevents and kills heartworms along with roundworms and hookworms. You can give this tasty product to your dog once a month to protect them from heartworm, and you need to choose the correct one based on your dog’s weight.

Simparica Trio
  • Protects dogs against heartworms, roundworms, and hookworms
  • Also works as a flea and tick preventative
  • Chewable pill with a liver flavor

Simparica Trio not only protects dogs against heartworms, but it can also prevent fleas, ticks, roundworms, and hookworms. Thus, it’s a heartworm and flea/tick preventative all in one chewable tablet. It can even kill fleas before they lay eggs to prevent a flea infestation in your home. While the texture is closer to a traditional pill, it has a liver flavor that most dogs will enjoy. It has six different weight ranges, so make sure the one you choose fits your dog’s size.

Tri-Heart Plus
  • Protects against heartworms, roundworms, and hookworms
  • Kills larvae before they reach your dog's heart
  • Chewable beef-flavored tablets

Tri-Heart Plus protects dogs from heartworms and other dangerous parasites like roundworms and hookworms. The tablet keeps your dog safe by killing the larvae of these pests before they reach your dog’s heart. Plus, the round, chewable tablets are beef-flavored, allowing you to serve them to your dog as a treat. They’re available in three different weight categories to ensure they’re effective for your dog’s size.

  • Prevents heartworms, hookworms, roundworms, and whipworms
  • Also kills fleas and prevents flea infestations
  • Beef-flavored tablets

Trifexis serves multiple purposes for your dog by preventing heartworms, killing fleas to prevent infestations, and treating and controlling intestinal worms like hookworms, roundworms, and whipworms. However, dog parents should be aware that Trifexis doesn’t work against ticks. The chewable tablets, which are available for a variety of weights, are beef-flavored so most dogs will take them every month as if they’re treats.

  • Fights heartworms, hookworms, roundworms, and whipworms
  • Controls flea populations and prevents flea eggs from developing
  • Beef-flavored tablets

Sentinel is another heartworm preventative that also benefits other areas of your dog’s health, such as fighting fleas, hookworms, roundworms, and whipworms. It prevents flea eggs from developing so infestations don’t occur. Unfortunately, it’s not designed to prevent ticks though. This is another preventative with a beef flavoring, so most dogs will happily eat it like any other treat. It’s available for four different weight groups, so choose the one that matches your dog’s size.

Frequently Asked Questions

How Long Do Dogs with Heartworms Live?

The lifespan of dogs with heartworms can vary greatly depending on the severity of the infection, the dog’s overall health, and whether they receive treatment. Untreated, heartworm disease can lead to severe organ damage and heart failure, significantly shortening a dog’s life, often within just a few years. However, with prompt and proper treatment, many dogs can recover and live a normal lifespan, although the treatment process can be risky and challenging.

Do Heartworms Ever Go Away?

Heartworms do not go away on their own; they require proper medical treatment to be eliminated. Without treatment, heartworms can live in a dog’s body for 5 to 7 years. Therefore, it’s essential to seek veterinary care for effective treatment and to prevent the severe health complications associated with this condition.

Do I Need to Test My Dog for Heartworms Every Year?

Yes, it’s recommended to test your dog for heartworms every year. Annual testing is crucial, even if your dog is on regular heartworm prevention, to ensure that the prevention program is working and to detect any infections as early as possible. This annual testing is a key part of maintaining your dog’s health and preventing the serious complications of heartworm disease.

Is Heartworm Common in Certain Areas?

Heartworm is more common in certain areas, particularly those with warmer climates and higher mosquito populations, as mosquitoes are the primary carriers of the disease. Regions with long mosquito seasons, such as the southeastern United States, tend to have higher rates of heartworm infection. However, heartworm has been reported in all 50 states in the U.S., making prevention important regardless of location.

Is Heartworm Disease Contagious?

Heartworm disease is not contagious between animals through direct contact. It’s transmitted exclusively through the bite of an infected mosquito, which means a mosquito must bite an infected animal and then bite another animal to spread the disease. Therefore, pets cannot directly infect each other with heartworms.

Can Humans Get Heartworm?

Humans can become infected with heartworm, but it’s extremely rare. In humans, heartworms do not usually complete their life cycle, so they may remain in the lungs, often mistaken for lung nodules in medical imaging. However, these cases are uncommon, and the worms generally do not cause significant health problems in humans.

At What Age Should You Start Giving Heartworm Preventatives to Your Dog?

It’s recommended to start giving heartworm preventatives to puppies as early as 6 to 8 weeks of age. This early start is crucial since puppies can be infected with heartworms as soon as they’re bitten by an infected mosquito. However, talk to your vet before starting your dog on heartworm prevention.

Happy dog at vet

Final Thoughts

All dog parents need to be aware of heartworm disease, which includes getting their dog tested annually and giving monthly preventatives. Doing so can help your furry friend live the long, healthy life they deserve. After all, it’s always better to be safe than sorry when it comes to your dog’s health and well-being.

iHeartDogs is reader-supported. When you buy via links on our site, we may earn an affiliate commission at no extra cost to you.

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