Canine Heartworm Disease (Cardiopulmonary Dirofilariasis)
- Occurrence: rarer
- Location of disease: Chest
When to visit the vet?
Urgent see a veterinarian within 24 hours
If the condition worsens / symptoms persist, consult a veterinarian.
The most important facts at a glance
Canine Heartworm Disease is caused by parasitic nematodes called heartworms that reside in the cardiovascular system. The Parasite is transmitted by mosquito bites, which inject microscopic larvae, called microfilariae, into the dog. These develop into adult worms in the dog, infecting the heart and blood vessels. The risk of infection is particularly high in warm, humid climates.
Symptoms include chronic Cough, shortness of breath, Weight loss, and heart murmurs. Severe cases can cause Cardiovascular collapse or sudden Death. Diagnosis is made through clinical signs, blood tests, and imaging procedures such as X-ray or ultrasound. Antigen tests and blood tests help confirm the infection. Therapy involves medication to kill the worms and requires restricted activity for the dog to avoid complications. In some cases, additional medications are used against microfilariae or secondary infections.
The prognosis depends on the stage of infection at Diagnosis. Early detection and therapy improve the chances of recovery, while advanced infections are more difficult to treat. Prevention is crucial and includes regular preventive medication as well as mosquito control measures. Regular veterinary examinations are important to monitor the dog’s health and respond promptly to infections. A comprehensive Prevention plan in collaboration with a veterinarian offers the best protection against this disease.
Causes
Heartworms are parasitic nematodes that reside in the cardiovascular system of dogs. The life cycle of Dirofilaria immitis begins when an infected mosquito bites a dog, transmitting microscopic larvae, known as microfilariae. These microfilariae develop into adult worms in the dog’s body over several months, eventually infecting the heart and adjacent blood vessels.
Mosquitoes are the primary vectors of heartworm disease. In endemic areas, particularly in warm, humid climates, the risk of transmission is particularly high. Factors such as temperature and humidity influence the development rate of microfilariae in the mosquito, which in turn affects the incidence of infections in dogs.
Once inside the dog’s body, the larvae migrate through the bloodstream and settle in the lungs and heart. There, they mature into adult worms within about six months, which can grow up to 30 cm long. These adult worms can survive in the host for several years, but can cause significant damage to the cardiovascular system.
Symptoms
The symptoms of heartworm disease can vary depending on the severity of the infection and the number of worms. In early stages, dogs may be asymptomatic or show only minor signs. However, as the infection progresses, serious symptoms can occur.
Common symptoms include chronic Cough, shortness of breath, Lethargy after moderate activity, and loss of appetite. Some dogs may also show Weight loss, Pallor of mucous membranes, and an enlarged liver. In severe cases, Heart failure or a blockage of the large blood vessels can occur, leading to sudden Cardiovascular collapse or even Death.
It is important to note that some dogs may show few or no signs despite a significant heartworm burden. This makes regular check-ups and tests particularly important to enable early Diagnosis and therapy.
Therapy
Treatment for heartworm disease is complex and requires a careful, step-by-step approach to minimize the risk of complications. The first step is usually to kill the adult worms with a drug specifically targeting Dirofilaria immitis. Melarsomine is one of the most common drugs for this purpose and is usually administered through a series of injections.
In addition to medication, it is important to severely restrict the dog’s activity during the recovery phase to minimize the risk of embolism from dying worms. This rest period can last several weeks to months, depending on the severity of the infection and the dog’s response to therapy.
In some cases, additional therapy may be required to eliminate microfilariae in the blood or to treat secondary infections. Antibacterial medications such as doxycycline can also be used to kill bacteria that live in symbiosis with heartworms and can contribute to the pathogenesis of the disease.
Therapy should always be carried out under the supervision of a veterinarian, as the therapy involves risks and must be individually tailored to each dog.
Prognosis and follow-up care
The prognosis for dogs with heartworm disease depends on various factors, including the stage of the disease at the time of Diagnosis, the number of worms, and the presence of complications. In early stages, if the infection is detected and treated promptly, the prognosis is generally good, and many dogs can make a full recovery.
In advanced stages or with severe heartworm burden, the prognosis may be more guarded. Complications such as Heart failure or severe lung damage can complicate therapy and reduce survival chances. Early Diagnosis and a targeted treatment plan are crucial to minimize the risk of serious consequences.
Even after successful therapy, regular follow-up care is important to ensure that no new infections occur and to monitor the dog’s long-term health.
Prevention
Prevention of heartworm disease is crucial to minimize the risk of infection. There are several effective medications for Prevention that can be administered regularly to prevent the development of heartworms. These preparations kill microfilariae before they can develop into adult worms.
Preventive medications include monthly tablets or spot-on preparations that can be prescribed by a veterinarian. It is important to administer these preventive measures consistently throughout the year, especially in regions with a high risk of infection.
In addition to medicinal Prevention, mosquito control measures can be helpful to reduce the risk of bites and thus infections. These include the use of mosquito repellents and avoiding outdoor activities in mosquito-rich areas during dusk and early morning.
Regular veterinary examinations and tests are also crucial to monitor the dog’s health and respond promptly to signs of infection. A comprehensive Prevention plan developed in collaboration with a veterinarian offers the best protection against heartworm disease.
Outlook on current research
Cardiopulmonary dirofilariasis is heartworm disease caused by Dirofilaria immitis. It is transmitted by mosquitoes; the adult worms reside primarily in the pulmonary arteries and, in heavier infections, also in the right heart. Research and clinical development currently focus on three goals: earlier diagnosis, safer therapy, and better prevention in regions with increasing spread. (merckvetmanual.com, heartwormsociety.org)
A particularly important research field is the resistance issue. The preventive macrocyclic lactones remain central, but there is evidence of reduced susceptibility in individual parasite populations. Therefore, intensive work is being done on molecular markers, better monitoring, and strategies to detect true resistance earlier. In parallel, researchers are investigating how climate change, mosquito ecology, and animal movements affect geographic distribution. (frontiersin.org, heartwormsociety.org)
A second focus is therapy optimization. The standard approach in dogs remains adulticide-oriented; additionally, Wolbachia-targeted adjunctive therapy with doxycycline is scientifically significant because these bacterial endosymbionts contribute to Inflammatory conditions and disease burden. In the future, combined approaches involving better diagnostics, resistance monitoring, vector control, and individualized therapy are likely to further improve treatment. (heartwormsociety.org, parasitesandvectors.biomedcentral.com)
Frequently Asked Questions (FAQs)
1. What is cardiopulmonary dirofilariasis?
2. How do dogs become infected?
3. What Symptoms does an infected dog show?
4. How is the diagnosis made?
5. How is heartworm disease treated?
6. Why is strict rest during therapy so important?
7. How effective is prophylaxis?
8. Is the disease dangerous for humans?
9. Can the disease be cured?
10. What should be considered when importing a dog from the Mediterranean region?
Literature
- American Heartworm Society. (2024). Current canine guidelines for the prevention, diagnosis, and management of heartworm (Dirofilaria immitis) infection in dogs (Revised 2024). American Heartworm Society.
- European Scientific Counsel Companion Animal Parasites. (2025). Worm control in dogs and cats (ESCCAP Guideline 01, 7th ed., version 21). ESCCAP.
- Noack, S., Harrington, J., Carithers, D. S., Kaminsky, R., & Selzer, P. M. (2021). Heartworm disease—Overview, intervention, and industry perspective. International Journal for Parasitology: Drugs and Drug Resistance, 16, 65–89. https://doi.org/10.1016/j.ijpddr.2021.03.004
- Romito, G., Pane, E., Guglielmini, C., Poser, H., Valente, C., Paradies, P., Castagna, P., Mazzoldi, C., & Cipone, M. (2024). Efficacy and tolerability of the American Heartworm Society therapeutic protocol in dogs affected by heartworm disease without caval syndrome. Journal of Small Animal Practice, 65, 39–46. https://doi.org/10.1111/jsap.13677
- Dantas-Torres, F., Ketzis, J., Pérez Tort, G., Mihalca, A. D., Baneth, G., Otranto, D., Watanabe, M., Linh, B. K., Inpankaew, T., Borrás, P., Arumugam, S., Penzhorn, B. L., Ybañez, A. P., Irwin, P., & Traub, R. J. (2023). Heartworm adulticide treatment: A tropical perspective. Parasites & Vectors, 16, Article 148. https://doi.org/10.1186/s13071-023-05690-8
- Prichard, R. K. (2021). Macrocyclic lactone resistance in Dirofilaria immitis: Risks for prevention of heartworm disease. International Journal for Parasitology, 51(13–14), 1121–1132. https://doi.org/10.1016/j.ijpara.2021.08.006