If you are reading this, you are probably suspecting your dog might have caught heartworms, or perhaps you want to know the heartworm symptoms in dogs

Did you know that heartworms could be silently affecting your dog’s health? That’s why it’s super important to know the symptoms of these obnoxious guys. Knowing the symptoms, you can quickly catch the infection and treat your dog ASAP. Early treatment can make a massive difference in the outcome. And, of course, by being informed about heartworms, you can take steps to prevent them from affecting your dog in the first place.

So, what is heartworm disease?

Heartworm disease in dogs is a severe condition caused by a parasite called Dirofilaria immitis, which is spread by the bite of a parasite-loaded mosquito. The parasite grows into long, thin worms that live in the heart and main arteries of the lungs, causing damage to the heart, lungs, and other organs.

If left untreated, heartworms can lead to heart failure, lung disease, and other serious health problems in dogs.

It is essential to be aware of the symptoms of heartworm and take steps to prevent it in your dog.

How common is heartworm disease in the US?

Heartworm is widespread throughout the United States, especially near the Eastern and Gulf coasts and in the Mississippi River Valley. Still, it looks like this infestation in dogs is on the rise in many parts of the USA.

In general, the parasite does not thrive in cooler areas. While living in the mosquito’s body, the worms need a daily temperature of 18° C or 64 ° F for at least one month to develop into a dog-threatening parasite.

Heartworms are most likely to spread during the hottest months of July and August, especially in places with temperate climates in the Northern Hemisphere.

Cats can also become sick with heartworms, but they are more resistant to infection than dogs.

Life Cycle of Heartworm in Dogs

The life cycle of a heartworm is the summary of the steps necessary for the parasites to grow and spread in a dog’s body.

Here are the simplified milestones of the life cycle of heartworm in dogs:

  • Heartworms are transmitted to dogs through the bite of an infected mosquito.
  • The mosquito carries the heartworm larvae and introduces them into dogs’ bloodstream when they bite.
  • The larvae mature and develop into adult worms in the heart and blood vessels of the dog’s lungs.
  • Females mate with male heartworms and produce microfilaria (baby heartworms) that circulate in the dog’s bloodstream
  • When another uninfected mosquito bites the dog, it ingests the microfilaria and carries them to another host, starting the cycle anew.
    Heartworm symptoms in dogs can be better understood and prevented when first knowing the biological cycle of the heartworm in nature and how dogs are involved on it

    Adult heartworms can live for several years in the dog’s body, causing gradual damage to the heart, lungs, and other organs.

    You will probably be amazed that adult heartworms can live for 5 to 7 years.

    In case you want to know, female heartworm adults are about 22 cm (8.7 inches) long, and males are smaller, about 14 cm (5.5 inches) long. Because of such a size and where they locate (heart and lungs) is that they wreak havoc inside the dog’s body.

    Do heartworms have particular preferences?

    Heartworms are not very picky. For example, heartworms do not discriminate based on breed. However, larger dogs that spend most of their time outside are at a higher risk of getting infected than smaller dogs that live primarily indoors because carrier mosquitoes are mostly outside.

    How about the age of dogs? Most affected dogs are between 4 and 8 years old, but dogs of any age, including young pups and elderly dogs, can get infected. Surprisingly, puppies under six months old are somewhat resistant to heartworms.

    How about the dog’s sex? Males are also more likely to get infected, with a 2 to 4 times higher rate than females.

    The length of a dog’s fur does not seem to impact their risk of infection.

    Magnified image of heartworms (Dirofilaria immitis). Image by animalhackers.com

    Heartworm Symptoms in Dogs

    So what are the heartworm symptoms in dogs? It depends on the stage of the disease. You want to notice the early symptoms so you can react fast, take your dog to the Vet, and start treatment before the condition becomes more serious.

    Early Symptoms of Heartworm

    The first symptoms of heartworm you may notice are:

    • Mild cough
    • Fatigue after doing exercise
    • Reduced appetite
    • Weight loss

    Early heartworm symptoms in dogs explained

    At the beginning of an infestation in a dog, heartworms can cause a mild cough due to adult worms in the lungs and heart. However, as the worms grow and multiply, they can obstruct blood flow in the lung’s blood vessels, resulting in fluid accumulation. This fluid buildup can lead to coughing as the dog tries to clear its airways. At first, the cough may be mild and occasional, but it may become more persistent and severe as the number of worms and fluid in the lungs increase. In some cases, if left untreated, heartworms can lead to life-threatening lung disease, making it essential to seek veterinary care if your dog is coughing or showing other symptoms of heartworm.

    Dogs with heartworm disease may feel fatigued after exercise due to the strain that the disease puts on their heart and lungs. Adult heartworms can obstruct blood flow in the lung’s blood vessels, leading to fluid accumulation and making it harder for the dog to breathe. This explains the fatigue, especially after physical activity, as the dog’s heart has to work harder to pump blood and oxygen to the rest of the body. In severe cases, heartworm disease can lead to heart failure and other serious health problems, making it even more challenging for the dog to participate in physical activity without becoming tired. Additionally, heartworms can cause anemia, which reduces the number of red blood cells and contributes to weakness and fatigue.

    Heartworm disease can also lead to a reduced appetite for various reasons related to the impact of the disease on the dog’s overall health. Heartworm disease can cause inflammation in the digestive tract, resulting in nausea and vomiting, making it difficult for the dog to eat. Heartworms can also cause pain and discomfort in the chest, especially during physical activity, making it challenging for the dog to eat and potentially leading to a reduced appetite. Weight loss also results as a consequence.

    Respiratory distress: Adult heartworms can obstruct blood flow in the lung’s blood vessels, making it challenging for the dog to breathe.

    REMEMBER: Seek veterinary care if you suspect your dog has heartworm so that they can make a treatment plan to help manage the disease and prevent further complications.

    Advanced Symptoms of Heartworm

    The more heartworm disease advances, the messier it becomes. One big part of the problem is that since this is a very high challenge for the dog’s body, the immune system fights to dead the heartworms. Unfortunately, this leads to powerful immune reactions in the affected tissues, predominantly the lungs and the heart.

    As the disease progresses, heartworm symptoms in dogs will be a combination of these:

    • Persistent Cough
    • Shortness of Breath
    • Reduced Activity Level
    • Abdominal Swelling
    • Collapse

    Advanced heartworm symptoms in dogs explained

    Cough persists due to the impact of the disease on the respiratory system. Adult heartworms can block blood flow in the lungs’ blood vessels, causing a buildup of fluid and making it more difficult for the dog to breathe. You will notice your dog will cough after any physical activity or when the dog is lying down. The cough may be dry and firm. In severe cases, the cough may be accompanied by gagging or retching and may become more persistent and challenging to control over time.

    Shortness of breath occurs because the heartworms hinder the blood flow in the lungs, avoiding the re-oxygenation of the blood. Also, the obstruction of the blood flow and the body’s immune reaction causes a buildup of fluid within the lungs making it more difficult for the dog to breathe. As heartworm disease progresses, shortness of breath may become more pronounced, making it increasingly difficult for the dog to breathe normally. For the same reasons, dogs become extremely tired, especially after exercise.

    Abdominal Swelling. Adult heartworms can block blood flow in the right side of the heart, making that blood travels back to the liver and other digestive organs, overflowing them. This causes a buildup of fluid in the abdomen, leading to swelling. This swelling can make it difficult for the dog to breathe and move comfortably and cause discomfort and pain.

    The overall problems caused by heartworms may produce aggravation of low appetite, weight loss, and reduced activity.

    Collapse. Dogs with heartworm disease may collapse due to the advanced stages of the disease, which can cause heart failure. In heart failure, the heart cannot pump enough blood to meet the body’s needs, causing various symptoms, including collapse. Additionally, the walls of the right heart (that pumps blood to the lungs for re-oxygenation) may thin in an effort to pump blood against a mass of heartworms inside it. In a nutshell, the heart is making a tremendous effort to compensate for the presence of heartworms.

    Just before a dog collapses, you may notice some warning signs, such as increased breathing difficulty, coughing, and fatigue. You may also notice a decrease in physical activity and a change in behavior, such as being less interested in playing or going for walks.

    If your dog collapses, you should immediately seek veterinary care. Collapse is a serious symptom and can indicate a life-threatening emergency. Your veterinarian can diagnose the underlying cause of the collapse and provide appropriate treatment to help your dog recover.

    REMEMBER: Early detection and treatment of heartworm disease can help prevent the progression of the disease and reduce the risk of serious complications, including collapse.

    How is heartworm disease diagnosed?

    Regular check-ups with a veterinarian are essential for diagnosing heartworm disease in dogs. During a routine check-up, your veterinarian can perform a thorough physical examination and review your dog’s medical history to look for any signs or symptoms of heartworm disease. Depending on what your Vet finds, a recommendation for diagnostic tests can arise.

    In summary, there are three basic means of diagnosis:

    • Blood Tests
    • X-rays
    • Echocardiography

    Blood tests will pick up the presence of microfilaria (baby heartworms) swimming along with blood cells. A common blood test measures the antigens (tiny fragments) of adult heartworms that may be floating around in the blood. In addition, some other changes in blood composition may indirectly indicate the presence of the heartworm, such as a reduced amount of red blood cells (anemia).

    X-ray and echocardiography images may show the damage made by the parasites.

    Echocardiography may show the worms directly in some cases, while X-rays can provide valuable information about the severity of heartworm disease in dogs. X-rays can show the size and shape of the heart, as well as the presence of fluid in the lungs, which may indicate the presence of heartworms.

    What to do next when you know your dog has got heartworms?

    • Medication: Your veterinarian may prescribe medication to help manage symptoms and support your dog’s recovery. It is crucial to give all medications as directed and to follow up with your veterinarian as recommended.
    • Rest: Your dog will need to rest during the recovery period to allow their body to heal. This period may include limited activity and exercise, as well as avoiding stairs, jumping, and other strenuous activities.
    • Lifestyle modifications: Your veterinarian may recommend changes to your dog’s diet and exercise routine to help support their recovery.
    • Follow-up appointments: Regular appointments with your Vet are essential to monitor your dog’s progress and ensure that they recover as expected.

    Please follow your veterinarian’s instructions. Call your Vet if you notice any changes in your dog’s health or behavior during recovery. With proper aftercare, many dogs can fully recover from heartworm disease and return to an active and healthy life.

    Recap of Heartworm Symptoms in Dogs

    Heartworm symptoms in dogs can include a mild cough, fatigue after exercise, reduced appetite, weight loss, persistent cough, shortness of breath, abdominal swelling, and in advanced cases, collapsing. Therefore, it’s essential to regularly check with your Vet to diagnose the disease and receive timely treatment to prevent further progression and complications.

    Early detection and treatment are key.

    Early detection and treatment of heartworm disease in dogs are crucial for the health and well-being of our pawfriends. Prompt treatment can prevent the progression of the disease and avoid serious health complications, such as heart failure and lung disease.

    Regular check-ups with a veterinarian and proper preventative measures, such as monthly heartworm preventives, can help ensure our dogs stay healthy and free from heartworm disease.

    Please don’t wait until it’s too late. Instead, act now to ensure the well-being of your furry companion. Check our article on how dogs get heartworms. This article outlines some of the best tips to prevent your dog from catching this nasty bug.


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