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Heartworm disease in dogs

A Guide to Prevent and Treat Heartworm in dogs 

Decreased appetite, weight loss, and fatigue – Are these the common signs you are noticing in your beloved pet these days? Although these signs could indicate a general ailment it could also point to something worse: heartworm disease. 

What is Heartworm?

What is Heartworm in dogs?

Dirofilaria immitis or heartworm is a parasitic roundworm that infects a variety of mammals. Although it is found throughout the world, much of the cases have been reported in the United States. Dogs are the natural host for these worms but most of them are also found in ferrets, humans, and cats.     

Heartworm infection is found to be serious and can be life-threatening in a few cases. Cats are atypical hosts since the worms in cats cannot survive to the adult stage. Although infections in humans have been reported, it has not been recognized as a human health issue.

Wondering how common is heartworm infection? The most common hosts for heartworms include wolves, domestic dogs, raccoons, and foxes. The parasites are spread by mosquitoes that bite an infected host and then pass on the parasite to other animals. Mansonia, Anopheles, and Aedes are the common mosquito species that can transmit heartworms. 

The life cycle of heartworms in dogs

The life cycle of heartworms in dogs 

Adult female heartworms release microfilariae in the bloodstream of an infected dog. Whenever a mosquito bites an infected dog, it gets infected with microfilariae, and under the right conditions over the next 10 to 14 days; they take the form of infective larvae. When this infected mosquito bites another dog, it spreads the larvae to the dog. 

The larvae then take about six to seven months to mature into adult heartworms in the newly infected dog. The lifespan of a heartworm is about 5 to 7 years inside a dog. The males can reach about 4 to 6 inches in length whereas the females reach about 10 to 12 inches in length. 

Signs of heartworms in dogs

Signs of heartworms in dogs

In heartworm condition, it is tough to diagnose what is wrong with your pet during the initial stages. As the condition progresses slowly, several months and even years may pass before the signs actually become obvious. 

Your canine friend may actually have a large worm burden before the symptoms actually show up. By this stage, the worms already start interfering with the movement of valves in the heart thereby resulting in a disruption in the flow of blood. Also, the blood vessels may become clogged with the worms thereby causing immense strain on the heart.

The kind of symptoms in your dog depends on the stage of the life cycle of heartworm. You need to remember that these symptoms could also be the signs of other conditions as well. Here are the warning signs that your dog may have heartworms. 

  • Persistent cough

Unlike kennel cough or regular cough, which is sporadic and strong, the cough related to heartworm is persistent and dry. In the initial stage, even mild exercise can induce cough. This is because the heartworms make their way to the lungs thereby causing blockage and discomfort. 

  • Lethargy 

If your pet suddenly loses interest in remaining active or going for walks, then it could be a sign that your dog may have heartworm disease. With the worsening of the condition, any level of physical activity can become strenuous for your dog. 

  • Weight loss

If the condition becomes severe, it becomes difficult for dogs to muster enough energy to perform even the simplest tasks. Regular activities such as enjoying a snack or having regular meals can also prove taxing for dogs thereby contributing to rapid weight loss.  

  • Difficulty breathing 

Once the heartworms have matured, they can make their way into the veins and lungs of the dog resulting in severe blockage. They may experience breathing issues that may seem more like an asthma attack. There can also be fluid buildup around the blood vessels in the lungs making it difficult for the lungs to oxygenate the blood.  

  • Bulging ribs 

Once the fluid buildup in the lungs progresses, you may notice that your dog’s chest is protruding. The ribs will also appear to bulge due to rapid weight loss.  

At a later stage, all the above-mentioned symptoms will become heightened and more complications will start to surface. The consistent signs of late-stage heartworm infection include

  • Heart murmur 
  • Enlarged liver
  • Abnormal sounds from the dog’s lungs 
  • Heavy worm burden can cut down blood flow to the heart and may cause “Caval syndrome” which ultimately leads to heart failure. 

How can you diagnose heartworm in a pet?

How can you diagnose heartworm in a pet?

Having your pet tested regularly at the vet is the best thing you can do to protect your beloved companion from the condition. A simple blood test can also reveal if your dog has been infected. Prevention is always the best option. Hence, you need to keep up with your pet’s heartworm medication to ensure that they remain healthy. 

Can heartworms be treated?

Can heartworms be treated 

Yes. The condition can be treated but it is best to always aim for prevention rather than treatment. Diagnosing the condition can be challenging and some advanced treatments for this condition can result in severe side effects.  

Identifying the problem is the first step towards recovering from the condition. Once the condition has been identified, the next goal would be to kill all the immature and adult worms while keeping the side effects to a minimum during the course of treatment. The process is difficult and long. It could also be a painful experience for your dog. Also, there is no guarantee that your dog can recover fully from the condition. This is the reason why vets always stress on preventing the condition altogether.  

You need to follow the best course of action to ensure that your pet is free from heartworms. Preventing the condition altogether is the best thing which will save you and your pet from stress and also unnecessary expenses. Speak to your vet about prevention medications for heartworms.  

Tips for preventing heartworms

Tips for preventing heartworms

It takes just a single infected mosquito to start spreading the disease. One bite from a parasite carrying mosquito is enough to result in this life-threatening condition in your beloved pooch. The good news is that you can prevent the condition by taking a few simple steps. 

Following these three easy tips can keep your dog free from heartworms.   

  • Reduce the number of mosquitoes 

Controlling mosquitoes in your home and in your surroundings can be quite challenging. It is possible to keep the mosquito population in check but it is nearly impossible to eliminate them entirely. You also need to train your dog from venturing into puddles and other regions in your surroundings that could prove to be the breeding grounds for mosquitoes (Heare, 2017).  

Here are some measures that you can follow for minimizing the creation of mosquito habitats.

  1. Use screens in windows and doors to prevent mosquitoes from entering your home
  2. Eliminate standing water both outdoors and indoors to prevent mosquitoes from breeding
  3. Use bug spray to kill mosquitoes
  4. Keep your home dry and cool as hot and humid environments are enough to make them comfortable to breed
  • Use a preventive

There is no way dogs can hide from mosquitoes. Using preventives can protect your dog from the condition altogether. Preventives affect the heartworm larvae before they get a chance to grow into adults and cause real harm to your pet. You can request your vet to administer preventative products. Following a balanced diet and a proper health care regimen will also help. 

  • Regular testing 

It is vital to carry out regular checkups to ensure that your dog remains free from the condition. You need to have your dog tested at least once a year. The process is quite simple and requires just a small blood sample of your pet. This can be done during your pet’s annual vet visit. 

By investing in heartworm preventive care, you will have the peace of mind that your dog has a greater chance of leading a healthy life. You can speak to your vet about the best options available for your pet. 

Treating heartworm in dogs 

Treating heartworm in dogs 

  • Both intravenous and topical drugs are available for treating heartworms. The treatment plan followed depends on the stage and severity of the condition. 
  • In dogs with caval syndrome, surgical removal of worms is the only treatment option available. Without this, most dogs will die from the disease. 
  • Using FDA-approved productions for preventing the infection in dogs. These have to be given either monthly or according to the veterinarian’s prescription. 

What happens if my dog tests positive for heartworms?

What happens if my dog tests positive for heartworms?

Nobody would want to hear that their dog has been infected with heartworms. Most dogs can be treated successfully depending on the stage of the condition. When the dog starts showing signs of the disease, the goal becomes to stabilize the condition first. Killing adult and immature worms becomes necessary as soon as the condition is identified. 

Here is what you can expect if your pet tests positive for the condition. 

  • Confirming the diagnosis

Once your dog tests positive, the diagnosis has to be confirmed with another test. This is because the entire treatment is complex and expensive. Hence, your vet would want to double-check if there is a need for the treatment. 

  • Restrict physical activity

This can be a tough requirement but you need to adhere to it. This is extremely important in cases where a dog is accustomed to being active. Any physical exertion can shoot up the rate at which heartworms can cause damage in the heart and lungs. The more severe the condition is, the less activity your dog needs to have.    

  • Stabilize your dog’s condition 

Before proceeding with the treatment, your dog’s condition has to be stabilized with appropriate therapies. If the condition of your dog is serious, then stabilizing the condition may require several months. 

  • Administer treatment 

Once your vet has decided that your dog’s condition is stable, then they will recommend a standard protocol that may involve numerous steps. The American Heartworm Society has laid down various guidelines for developing a course of treatment. Dogs with mild symptoms such as exercise intolerance and cough usually have a high success rate during treatment. In more severe cases, the complications are greater. However, the severity of the condition does not always correlate with the severity of the symptoms.   

  • Testing for success

Once the treatment has been completed for about six months, your vet will perform a test to confirm that all the parasites have been eliminated from the system. To avoid the possibility of contracting the disease again, the vet will have to administer preventives year-round or for the rest of your pet’s life.

Prevention is the best treatment

Prevention is the best treatment

There are several FDA-approved products available for preventing heartworm condition in dogs. You will have to get a veterinarian’s prescription and adhere to the schedule provided. Most of the heartworm preventive medications have to be given on a monthly basis. They are given either as an oral tablet or can be applied on the skin as a topical liquid.   

Preventives are available as both chewable and non-chewable oral tablets. The product has to be injected under the skin once every six to twelve months. Some heartworm preventives have ingredients that are also effective against intestinal worms such as hookworms and roundworms. Opting for year-round prevention is the best thing you can ever do to safeguard your dog against heartworms.


  1. Jones S., (2015). Canine Caval Syndrome Series, Part 1: Understanding Development of Caval Syndrome. Today’s Veterinary Practice.
  2. Food and Drug  Association. (2019). Keep the Worms Out of Your Pet’s Heart! The Facts about Heartworm Disease. FDA Gov.,the%20bite%20of%20a%20mosquito.
  3. American Heartworm Society. (2018). Heartworm Life Cycle Illustration. American Heartworm Society Org.
  4. KHTS. (2020). 10 Facts And Myths About Heartworm Infection In Dogs That Pet Owners Must Know. Homestation Website.
  5. Heare, J. O. (2017). The Science and Technology of Dog Training . Ottawa, Canada : BehaveTech Publishing.
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