Heartworm Disease In Dogs

Heartworm disease is a dangerous and often overlooked threat to the well-being of your beloved pets. This serious condition, caused by the parasitic worm Dirofilaria immitisHeartworm disease, which is spread through mosquito bites, can cause irreversible damage to the heart and lungs of dogs, cats, and ferrets, highlighting the severity of heartworm disease. Without early detection and treatment of heartworm disease, heartworm infection in dogs can be fatal. But the good news is, with the right knowledge and preventive care, you can protect your pet from this silent killer. Dive into this essential guide to learn how to keep your furry family member safe from heartworm disease.

Key Takeaways

• Heartworm disease is caused by the parasitic worm Dirofilaria immitis Heartworms are primarily spread through mosquitoes, which are vectors for heartworm disease in dogs.
• Symptoms include persistent cough, fatigue, breathing difficulties, and weight loss in advanced stages.
• Monthly preventive medications are crucial, starting as early as 8 weeks old.
• Annual heartworm testing and regular vet check-ups are recommended even for dogs on preventive medication.
• Heartworm treatment involves melarsomine dihydrochloride injections, requiring strict rest and follow-up care.

What is Heartworm Disease?

Heartworm disease is a serious condition caused by the parasitic worm Dirofilaria immitis, primarily affecting dogs, cats, and ferrets. These worms are transmitted through mosquito bites, where the mosquito serves as an intermediate host, carrying the larvae from an infected animal to a healthy one. Once inside a dog, the larvae mature into adults that inhabit the heart, lungs, and blood vessels, leading to severe lung disease, heart failure, and even death if untreated.

Therefore, prevention is crucial, with monthly medications recommended to kill larvae before they mature. To ensure effective prevention of heartworm disease, starting these preventives early, around 8 weeks in puppies, is essential for long-term health.

What is the Life Cycle of the Heartworm?

The life cycle of the heartworm is complex and requires a mosquito as an intermediate host to complete its development in a dog.

It begins when a mosquito bites an infected dog and ingests microfilariae—young heartworms—present in the dog’s bloodstream. Over the next 10 to 14 days, these microfilariae develop into infective larvae within the mosquito’s gut, eventually migrating to its mouthparts. When the mosquito bites another dog, it deposits these infective larvae onto the dog’s skin, allowing them to enter the new host’s bloodstream. Once inside the dog, the heartworm larvae travel through the bloodstream, reaching the heart and pulmonary arteries, where they mature into adult heartworms within 6 to 7 months, leading to potential clinical signs of heartworm disease.

This maturation phase is critical as adult heartworms, which can live for five to seven years, cause severe damage to the heart, lungs, and blood vessels, leading to significant health issues like coughing and shortness of breath.

Where is Heartworm Disease Found?

Heartworm disease is found across the globe, with particularly high prevalence in regions with warm climates that support mosquito populations, the primary transmission vector for heartworm infection in dogs. In the United States, the heartworm disease is most common along the Atlantic and Gulf coasts, from the Gulf of Mexico to New Jersey, and along the Mississippi River and its major tributaries, affecting both dogs and cats. However, it has been reported in all 50 states, making it a nationwide concern. Globally, different geographic hotspots for heartworm disease exist, such as the southeastern U.S. and certain regions in Canada like southern British Columbia and Ontario, where signs of heartworm infection include coughing and lethargy.

The risk is significantly higher in areas with high mosquito activity, especially near water bodies, which are ideal breeding grounds for these vectors. Here’s a table to help you understand the prevalence in various regions:

Region	Climate Influence	Risk Level
Southeastern United States	Warm, humid	Very High
Western Europe	Mild, seasonal variation	Moderate
Central America.	Tropical, year-round warm	High
Southern Japan	Subtropical, seasonal rain	Moderate
Southern British Columbia	Temperate, seasonal	Moderate

Whether you’re living in a high-risk area or traveling with your pet, knowing these facts can guide you in taking preventive actions to protect your dog from heartworm disease.

Learn more about community efforts to combat heartworm disease: https://anipetshop.com/dog-care/heartworm-awareness-month/

What are the Symptoms of Heartworm Disease in a Dog?

The symptoms of heartworm disease in a dog often develop gradually and are closely related to the number of worms present (the worm burden), the duration of the infection, and the dog’s overall activity level. Initially, dogs with a low worm burden or those that have been recently infected may show few to no symptoms, while more active dogs or those with a heavier worm burden often exhibit symptoms earlier and more severely.

Heartworm disease is typically categorized into four classes or stages, each with progressively worse symptoms:

• Class 1: Dogs may show no symptoms or only mild signs like an occasional cough.
• Class 2: Symptoms become more noticeable, including a persistent cough and tiredness after moderate activity.
• Class 3: The symptoms are more severe, including a sickly appearance, persistent coughing, and fatigue even after mild activity. Dogs at this stage may also experience trouble breathing, and signs of heart failure become apparent. Chest x-rays typically reveal changes in the heart and lungs due to the disease’s progression.
• Class 4: Also known as caval syndrome, the worm burden is so heavy that it physically blocks blood flow back to the heart. This life-threatening condition is characterized by sudden cardiovascular collapse, labored breathing, pale gums, and dark, bloody urine. Without prompt and risky surgical intervention to remove the blockage, survival from heartworm infection in dogs is rare.

As the disease advances, you may also notice significant weight loss, loss of appetite, and swelling of the belly due to fluid accumulation (ascites), which indicates severe heart failure. If left untreated, heartworm disease will inevitably progress, causing irreversible damage to the heart, lungs, liver, and kidneys, and eventually leading to death.

How Significant is My Pet’s Risk for Heartworm Infection?

Your pet’s risk for heartworm infection is influenced by a variety of factors, including geographic location, mosquito activity, and exposure to untreated animals. While some areas may seem to have a lower prevalence of heartworm, it’s crucial to consider that the disease has been diagnosed in all 50 states and is continuing to spread to new regions each year.

Mosquitoes, the primary carriers of heartworm, thrive in warm, humid climates, making these areas particularly high-risk. However, even in regions with lower mosquito activity, the risk is not negligible, as mosquitoes can travel great distances, often carried by the wind, and easily enter homes, putting both outdoor and indoor pets at risk. Additionally, the movement of infected pets to new areas can introduce heartworm to previously unaffected regions, as seen in the widespread relocation of pets following natural disasters like Hurricane Katrina.

Another significant consideration is the presence of wildlife carriers such as coyotes, wolves, and foxes, which can maintain and spread heartworm within local ecosystems. Because of these unpredictable variables, heartworm rates can vary dramatically from year to year, even within the same community. Thus, it is essential to remain vigilant and proactive in protecting your pet, regardless of your location, by understanding these risk factors and taking appropriate preventive measures.

When Should My Dog be Tested?

The American Heartworm Society recommends a ‘Think 12’ approach: provide your dog with year-round heartworm prevention and ensure they are tested for heartworm every 12 months to catch any signs of heartworm disease early.

Here are guidelines on testing and timing:

• For puppies under 7 months old, heartworm prevention can begin without an initial test, but testing should be done 6 months after starting prevention, followed by another test 6 months later, and then annually.
• Adult dogs over 7 months old who have not previously been on preventive medication need to be tested before starting prevention, with follow-up tests at 6 and 12 months, and then yearly.
• If there has been a lapse in prevention, immediate testing is required, followed by a test 6 months later and annually thereafter.

Annual testing is important even if your dog is on consistent heartworm prevention, as no medication is 100% effective. Missing a dose or administering it late can leave your dog vulnerable, and even when given correctly, there’s a slight chance of infection. Regular testing ensures that any infection is caught early, allowing for prompt treatment and minimizing the risk of severe complications.

How is Heartworm Disease Diagnosed?

A veterinarian performs blood tests to screen a dog for heartworms, using an antigen test to identify specific proteins released by adult female heartworms into the dog’s bloodstream. In most cases, these antigen tests are highly accurate in detecting infections when one or more adult female heartworms are present.

Heartworm disease is primarily diagnosed through simple blood tests, which are essential for detecting the presence of heartworms. The most common test is a serological test, such as the antigen test (ELISA), which identifies specific proteins released by adult female heartworms into the bloodstream. If the test is positive, additional diagnostic procedures are often required to evaluate the severity of the disease and determine if the dog can safely undergo treatment. These may include:

• Chest X-rays (radiographs): Used to assess the extent of damage to the heart and lungs, which is crucial before starting any treatment.
• Echocardiography (heart ultrasound): Helps evaluate the degree of heart enlargement and function, and can also detect the presence of worms in the heart and associated blood vessels.
• Bloodwork (complete blood cell count and serum biochemistry): Recommended to check for organ damage associated with heartworm disease, ensuring that the dog is healthy enough for treatment.

What Happens If My Dog Tests Positive for Heartworms?

If your dog tests positive for heartworms, it’s natural to feel concerned, but the good news is that most dogs can be successfully treated. The first step is to confirm the diagnosis with an additional test, as the treatment process is both complex and expensive, and your veterinarian will want to be certain that it’s necessary. Once confirmed, your dog’s physical activity should be restricted immediately to prevent further damage caused by the heartworms. In severe cases, your veterinarian may need to stabilize your dog’s condition with appropriate therapy before beginning the actual heartworm treatment, which could take several months.

The treatment protocol will be customized to your dog’s specific condition, often following guidelines from the American Heartworm Society. This may involve administering heartworm medication to kill both adult and immature heartworms, along with antibiotics to prevent complications. As an owner, it’s important to adhere strictly to the prescribed medication regimen and monitor your dog for any side effects, such as lethargy, difficulty breathing, or loss of appetite. Regular veterinary check-ups will be necessary to track your dog’s recovery and adjust the treatment plan as needed.

Approximately 9 months after treatment, your veterinarian will perform a heartworm test to ensure all heartworms have been eliminated. To prevent reinfection, heartworm prevention should be administered year-round for the rest of your dog’s life. Remember, managing heartworm disease is a long-term commitment, but with the right care, your dog can recover and enjoy a healthy, happy life.

How is heartworm disease treated?

The primary treatment for killing adult heartworms is an injectable drug called melarsomine dihydrochloride, available under the brand names Immiticide® and Diroban®. This arsenic-containing drug is FDA-approved and is administered through a series of deep injections into the dog’s back muscles, typically used for dogs with stabilized Class 1, 2, and 3 heartworm disease.

The treatment schedule for heartworm medication usually involves an initial injection followed by a 30-day rest period, then two more injections given 24 hours apart. This schedule is determined by the veterinarian based on the dog’s specific condition. After the injections, it is crucial to keep the dog completely rested, as the adult worms die within a few days and start decomposing, which is part of the treatment of heartworm. These dead worms are carried to the lungs, where they lodge in small blood vessels and are eventually reabsorbed by the body—a process that can take several weeks to months. During this time, the dog is at risk of complications, so strict exercise restriction is essential to prevent potentially life-threatening issues.

In addition to melarsomine, dogs are often treated with an antibiotic like doxycycline, which targets Wolbachia, a type of bacteria that live within the heartworms, enhancing the overall treatment for heartworm. This helps reduce complications and enhances the effectiveness of the treatment options available for heartworm disease.

To eliminate microfilariae, the dog is given a topical solution such as Advantage Multi® for Dogs, which contains imidacloprid and moxidectin, a common heartworm medication. This medication is applied to the dog’s skin and is FDA-approved to target the microfilariae circulating in the bloodstream. In some cases, dogs may need to stay in the hospital for observation when this medication is administered, and this is often done before starting the injections for adult heartworms. After completing the treatment, the dog will be started on a heartworm preventative to avoid reinfection.

There are also newer treatment protocols, such as the “Slow-Kill” method, which involves continuous monthly administration of a heartworm preventive along with oral doxycycline. However, this method is generally not recommended because it can take a year or more to kill all the heartworms, and during this time, the worms continue to cause damage. It also requires strict exercise restriction for a much longer period. This approach may be used in cases where the rapid-kill method poses significant risks, such as when the dog has an unrelated terminal illness or when melarsomine is unavailable.

Throughout the treatment process, close monitoring by a veterinarian is essential, and any severe reactions such as loss of appetite, shortness of breath, severe coughing, coughing up blood, fever, or depression should be reported immediately for prompt intervention. The veterinarian will select the most appropriate drugs and treatment protocols based on the dog’s specific condition to ensure the best possible outcome.

For a detailed breakdown of the treatment for heartworms in dogs, refer to our comprehensive guide.

How Do We Prevent Heartworm Disease in Dogs?

Many FDA-approved products are available to prevent heartworms in dogs, all of which require a veterinarian’s prescription. Most preventives are administered monthly, either as a topical liquid applied to the skin or as an oral tablet, with both chewable and non-chewable options available. Additionally, there is a product that can be injected under the skin every 6 or 12 months, but only a veterinarian can administer this injection.

Some heartworm preventives also contain ingredients that protect against other parasites, such as intestinal worms (like roundworms and hookworms), fleas, ticks, and ear mites. Year-round prevention is highly recommended to provide continuous protection, and it is essential to consult your dog’s veterinarian to determine the best preventive option tailored to your dog’s needs.

Discover effective strategies to prevent heartworm in dogs and keep your pet healthy

In addition to medication, reducing your dog’s exposure to mosquitoes is crucial in preventing heartworm infection. The American Heartworm Society advocates for the “Think 12” approach, which emphasizes giving dogs 12 months of heartworm prevention and having them tested for heartworms every 12 months. It is also recommended to use an FDA or EPA-approved insecticide designed for use on dogs to minimize mosquito bites.

Find out What To Do If You Miss a Heartworm Preventative Dose to learn more.

Other preventive measures include reducing standing water where mosquitoes breed and limiting outdoor activities during peak mosquito times, such as dawn and dusk. Even dogs who have been successfully treated for heartworms remain at risk of reinfection, so ongoing preventive care is essential. With the safe and affordable heartworm preventives available today, no dog should have to endure this dangerous disease. Consult with your veterinarian to establish the most effective heartworm prevention program for your dog and to recognize any signs of heartworm disease early.

Frequently Asked Questions

Can Pregnant Dogs Receive Heartworm Prevention Treatment?

Yes, pregnant dogs can receive heartworm prevention. However, the treatment of heartworm should be chosen carefully to ensure it’s safe for both the mother and her unborn puppies. Always consult your veterinarian to confirm that the selected preventive treatment supports the mother’s immune system and protects fetal health.

Could Genetic Factors Affect a Dog’s Susceptibility to Heartworms?

Yes, genetic factors can affect a dog’s susceptibility to heartworms. Some breeds may possess a robust immune response or inherited traits that influence their risk levels. Additionally, environmental conditions interact with these genetic factors, further impacting susceptibility.

Can dogs fully recover from heartworm?

Yes, if signs of heartworm disease are detected early and treated properly, your dog can potentially enjoy a good quality of life. However, some dogs may face clinical signs of complications either from the treatment or the disease itself, which could lead to lifelong health issues.

How expensive is heartworm treatment for dogs?

The cost of heartworm treatment for dogs typically ranges between $600 and $6,000, depending on factors such as the dog’s size, the stage of the disease, and the associated veterinary expenses. The standard treatment protocol usually involves blood tests and x-rays to assess the severity of the heartworm infection, as well as the administration of sedatives, pain medications, and antibiotics to eliminate the parasites.

For a detailed breakdown of potential costs, visit: https://anipetshop.com/dog-care/cost-of-treating-heartworm/

How Effective Is Heartworm Prevention Medication if a Dose Is Missed?

If you miss a dose of heartworm prevention, its effectiveness diminishes, putting your dog’s health at risk. Call your vet for guidance. They might suggest retesting your dog in six months to ensure complete heartworm protection.

Conclusion

By recognizing the importance of year-round prevention, regular testing, and prompt treatment for heartworm, you can safeguard your pet’s health and ensure a long, happy life. Remember, with effective preventive measures and awareness, heartworm disease is entirely avoidable. Stay informed, consult your veterinarian, and take the necessary steps to protect your furry companion from this hidden threat.

Remember that dogs of all ages need protection! Learn about heartworm prevention for older dogs

References:

• Lobetti, R., Brianti, E., Cassini, R., Calderini, P., Furlanello, T., Genchi, C., … Antognoni, L. (2021). Tick-borne pathogens in dogs living in different areas of Italy: Seroprevalence and risk factors. PLOS ONE, 16(8), e0255847. https://doi.org/10.1371/journal.pone.0255847

• Murphy, M., Six, R. H., Crane, M., Egan, J., & Thompson, L. A. (2019). Evaluation of the efficacy and safety of fluralaner topical solution (Bravecto®) for the treatment of ear mite (Otodectes cynotis) infestations on cats presented as veterinary patients in the USA. Parasites & Vectors, 12, 484. https://doi.org/10.1186/s13071-019-3702-6

• Traub-Dargatz, J. L., Little, S. E., Griffin, J., Blagburn, B. L., Bowman, D. D., Brooks, M. B., … Tell, L. A. (2019). American Heartworm Society guidelines for the prevention, diagnosis, and management of heartworm disease in dogs and cats. Parasites & Vectors, 12, 328. https://doi.org/10.1186/s13071-019-3633-2

• American Heartworm Society. (n.d.-a). Heartworms in dogs. https://www.heartwormsociety.org/heartworms-in-dogs

• American Kennel Club Canine Health Foundation. (n.d.-b). The heart of the matter. https://www.akcchf.org/educational-resources/library/articles/the-heart-of-the-matter.html