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Heartworm in Dogs: Symptoms of Heartworm Disease

Apr 2, 2024 | For Your Pet, Health Emergencies, Preventive Care

Heartworm disease poses a significant threat to our beloved pets, including ferrets, cats, and especially dogs. This sneaky ailment, if left untreated, can cause severe heart disease, heart failure, lung disease, other organ damage, and in serious cases, even death. 

Understanding Heartworm in Dogs 

Dog heartworms in alcohol in jarDogs are more susceptible to heartworms compared to other common household pets. This vulnerability stems from the fact that, biologically, dogs are natural hosts for these parasites. Heartworms can grow and reproduce easily inside the body of a dog. If heartworms in dogs are left untreated, it can result in them carrying many heartworms, sometimes reaching hundreds. The impact of heartworm disease goes beyond the mere presence of these parasites. It can lead to lasting physical damage directly to the dog’s heart causing blood clots. This can also cause proteins to be released into the dog’s bloodstream, causing inflammation to the lungs, liver, kidneys, and other tissues. Even after the removal of the parasites, the negative effects on the dog’s health and overall well-being may persist. Whether you are the pet parent of an older dog, or welcoming a new puppy, it is important to recognize heartworm symptoms in dogs and ensure that you are taking proper steps towards heartworm prevention. 



Heartworm Symptoms in Dogs 

In the initial stages of heartworm disease, many dogs may not display any noticeable symptoms, making it challenging to detect. The seriousness of the condition varies based on several factors: first, the number of worms present in the dog’s body (referred to as the worm burden), second, the duration of the infection, and third, how the dog’s immune system responds to the presence of the worms. Additionally, the level of activity the dog engages in also influences the severity of the disease and when symptoms become apparent. 

Dogs that are less active, recently infected, or have a low number of worms may not exhibit clear signs of heartworm disease. Conversely, dogs with a higher number of worms, those that are more active, or have been infected for a longer period are likely to display more pronounced symptoms. If you feel your dog is experiencing any of the symptoms below, bring them to your nearest AZPetVet location to determine the best course of treatment.  

Most Common Heartworm Symptoms in Dogs  

Persistent Cough 

A persistent, dry cough is frequently observed in dogs suffering from advanced heartworm disease. This cough, often unaccompanied by phlegm or other respiratory symptoms, serves as a crucial indicator of the condition’s progression. Interestingly, this cough may manifest as one of the earliest signs in an otherwise outwardly healthy canine. It’s essential for pet owners to recognize the significance of this symptom and promptly seek veterinary care if noticed in their furry companions. Early detection and intervention can significantly improve treatment outcomes and enhance the quality of life for dogs affected by heartworm disease. 

Lethargy and Lack of Energy 

Lethargy and reluctance to engage in physical activity are prevalent indicators observed in dogs afflicted with advanced heartworm disease. If you notice your dog showing disinterest in their usual walks or displaying unusual fatigue after even light activity, it could serve as a warning sign of underlying heartworm infection. These symptoms may appear subtly at first but can worsen over time if left untreated. Therefore, it’s imperative for pet owners to remain vigilant and seek prompt veterinary attention if such behavioral changes are observed in their furry companions. Early detection and intervention can significantly improve treatment outcomes and enhance the quality of life for dogs affected by heartworm disease. 

Difficulty breathing 

In the most advanced stages of heartworm disease, dogs may exhibit more pronounced respiratory distress, which can include symptoms such as rapid or labored breathing, in addition to persistent coughing. This escalation in respiratory issues signals a critical phase of the disease progression, necessitating urgent veterinary attention. The presence of rapid breathing alongside coughing indicates a heightened severity of the condition, requiring immediate intervention to alleviate discomfort and mitigate further complications. Pet owners must remain vigilant and proactive in monitoring their furry companions’ health, promptly seeking professional guidance if such symptoms manifest, to ensure timely diagnosis and appropriate management of heartworm disease. 

Swollen Abdomen/Stomach 

As heartworm disease gets worse, it can increase the risk of heart failure in dogs. One concerning sign of heartworm in dogs is a swollen belly due to a buildup of fluid, causing a condition known as ascites. This symptom is caused because the heart isn’t circulating blood as well as it should, leading to issues with blood flow and an increase in pressure within their circulatory system. As a result, fluid starts leaking into the belly area, making it look bigger. It’s important to notice this sign because it means the disease is getting serious. If you notice your dog experiencing this symptom, take them to your nearest AZPetVet right away to promptly treat heart failure and alleviate discomfort. 

Weight Loss/ Lack of Appetite 

In some cases of heartworm in dogs, you may notice a decrease in appetite, causing them to eat less and lose weight over time. This heartworm symptom can concern pet owners, especially if their dog was previously healthy and had a good appetite. A reduced interest in food may be accompanied by other signs of illness, such as lethargy or vomiting. It’s important to monitor your dog’s eating habits closely and consult with your AZPetVet veterinarian if you notice any significant changes. Addressing decreased appetite early can help prevent further complications and ensure your dog receives the care they need to recover. 

Caval Syndrome 

If heartworm in dogs progresses to an extreme case, dogs may encounter one of the most serious signs of heartworm disease: caval syndrome. Caval syndrome is caused by a severe lack of blood flow from the heart to the lungs due to a severe heart valve insufficiency. This causes a rupturing of red blood cells and lack of oxygen carrying capacity of the blood. This emergency situation is characterized by abrupt difficulty breathing, pale gums, dark bloody or coffee-colored urine, and always requires urgent surgical intervention. If you notice your dog experiencing any of these symptoms, bring them into your nearest AZPetVet location immediately, and our experienced veterinarians can help determine the best course of action for your furry friend. 

How Do Dogs Get Heartworm?  

Mosquito taking blood from petAt the core of heartworm disease lies a tiny yet formidable adversary: Dirofilaria immitis, a parasitic worm transmitted through the bite of an infected mosquito. Acting as an intermediate host, the mosquito carries these larvae briefly before transmitting them to their next victim with a single bite. Once inside the animal, typically a dog, the larvae mature into adult worms, setting up residence in the heart, lungs, and associated blood vessels, hence the name “heartworm” disease. 

The American Heartworm Society has stated that mature heartworms have a lifespan of approximately 5 to 7 years in dogs and 2 to 3 years in cats. With each mosquito season, there is a heightened risk for animals to contract the disease or for the number of worms in infected animals to multiply. This annual cycle of mosquito activity poses an ongoing threat to the health of our pets, making regular preventative measures crucial in safeguarding against heartworm infection. Therefore, pet owners should remain vigilant and proactive in protecting their furry companions throughout each mosquito season. 

Can my dog get heartworm from other dogs? 

Is heartworm contagious? Short answer, NO! Heartworm in dogs is not a contagious ailment, meaning that infected dogs cannot transmit this disease to non-infected ones. While direct transmission of heartworms from one dog to another is not possible, the presence of infected dogs in an area can increase the risk of heartworm transmission to other dogs.  

Infected dogs act as reservoirs for heartworms. Meaning that mosquitoes biting an infected dog can carry the parasite to a non-infected dog, thereby contributing to the overall prevalence of heartworm disease in the environment. Consequently, areas with a higher population of infected dogs, coyotes, foxes, and wolves and areas with a greater density of infected mosquitoes pose a greater risk of heartworm transmission to susceptible dogs. 

Can I get Heartworm from my Dog?  

No, heartworms cannot be passed on to humans directly from their pet. They’re transmitted exclusively through mosquito bites. Interestingly, most heartworm larvae perish while trying to travel through human skin. If they make it into the human bloodstream, it is possible for them to mature into mature heartworms, though most die before reaching this stage. The adult heartworms that mature in humans are sterile and cannot continue to reproduce.     

Heartworm Prevention for Dogs 

Through studies done by the American Heartworm Society, we now know that cases of heartworm in dogs have been reported in all 50 states. Knowing this information, it is important to consult your veterinarian about suitable heartworm prevention options for your dog.  

Dogs should receive annual heartworm testing, which can be done during your AZPetVet annual preventative care exam. It is recommended to continue annual testing, even if your dog is already on heartworm prevention medication. Though these medications are very effective, they cannot guarantee 100% prevention, so repeat testing is recommended yearly.  

Types of Heartworm Medications for Dogs 

Dog heartworm prevention medication can come in different forms such as chewable pills, ‘spot on’ (topical) medication, or injection.Dog taking heartworm medication Regardless of the form, approved heartworm prevention medications work by targeting and eliminating the immature stages of the heartworm parasite. This includes the larvae deposited by mosquitoes and the subsequent early growth stage that develops inside the dog. However, it’s crucial to note that heartworm larvae can mature into a juvenile/immature adult stage in as little as 51 days, making them more resistant to preventives.  

To effectively combat heartworms, it is important that dogs receive their heartworm medication on schedule, monthly for oral and topical products and every 6 or12 months for injectables. Delaying heartworm prevention can allow immature larvae to progress to the adult stage, which is less effective in protecting your pet. Therefore, adhering to the recommended preventive schedule is essential to safeguarding your pet’s health against heartworm disease. 

Heartworm Awareness Month 

happy man smiling hugging hugging dog close April is Heartworm Awareness Month, and at AZPetVet, we are dedicated to educating pet owners about the importance of safeguarding their furry companions against heartworm disease. As the weather warms up and mosquitoes become more active, the risk of heartworm transmission increases, making preventative measures essential for pet health. AZPetVet emphasizes the significance of regular heartworm prevention, advising pet owners to consult with their veterinarians to ensure they are using the most effective preventative medications. These medications work by targeting and eliminating immature heartworm larvae, preventing them from developing into adult worms that can cause serious health complications in pets. By raising awareness and providing educational resources throughout Heartworm Awareness Month, AZPetVet aims to empower pet owners to take proactive steps in protecting their pets’ health and well-being.  

What to do if Your Dog has Heartworm 

Heartworm diagnosis involves several methods, including blood tests, echocardiography, and X-rays. Blood tests can detect both adult worms and microfilariae (heartworm larva), while echocardiography is used to visualize worms in the heart and blood vessels. X-rays reveal abnormalities in the chest, which can indicate if heartworms are present. 

Discovering that your dog has heartworm can be distressing, but the good news is that treatment is often successful. The primary objective is to stabilize your dog’s condition if they’re displaying symptoms of the disease, then eliminate all adult and immature worms while minimizing treatment side effects. It’s important to limit your dog’s physical activity once the diagnosis is confirmed to prevent accelerated heartworm-related damage to the heart and lungs, especially in severe cases. 

It is important to note that damage caused by advanced heartworm disease is not reversible, so it is important to ensure you are regularly checking your dog for heartworms during their annual exams.  

Heartworm Treatment for Dogs  

If a dog tests positive for heartworm, treatment options are discussed by the veterinarian. This may include additional testing such as complete blood count, chemistry panel, antigen test, and urinalysis to assess organ function and overall health. 

Treatment for heartworm infection is tailored to each individual dog based on the severity of their symptoms and the results of diagnostic testing. For dogs in early stages of infection, treatment involves exercise restriction, medication administration, and melarsomine injections to kill adult worms. 

Without treatment, heart and lung damage worsen, leading to life-threatening conditions. However, with proper treatment, success rates are high for heartworm eradication, even for dogs with advanced heartworm disease. The 3-part injection of melarsomine is 98% effective at killing adult worms, and rest is crucial to help prevent pulmonary embolisms. 

Book/Request an Appointment with AZPetVet 

Don’t leave your furry friend vulnerable to the dangers of heartworm disease. Schedule a preventative care exam with us at your nearest AZPetVet location to discuss the most suitable preventative options for your pet’s unique needs. Together, we can ensure a happy, healthy future for your beloved companion. 

Disclaimer: Not intended to be a substitute for professional veterinarian advice, diagnosis, or treatment. Always seek the advice of your veterinarian with any questions you may have regarding the medical condition of your pet. If you think your pet has a medical emergency, call or visit your veterinarian or your local veterinary emergency hospital immediately.