Dog Lungworm Infection: Symptoms, Transmission Routes, and Treatment & Prevention Guide

Infection/ParasitesDiseasesMeongsiljang Veterinary Advisory Board

Our veterinary advisory team has compiled information on the causes, symptoms, diagnosis, treatment, and prevention of lungworm disease in dogs. If your dog has had a chronic cough for more than two weeks, it may not be a simple cold.

What Is Dog Lungworm Infection? — Definition and Key Points

A dog showing coughing symptoms outdoors — a typical image of heartworm infection

- What is lungworm disease?: Lungworm disease is a parasitic condition in which worms inhabit the lung tissue, bronchi, and pulmonary arteries, leading to chronic respiratory symptoms. - Why it’s hard to detect: In the early stages, symptoms often resemble a simple cough, making it difficult to distinguish from a cold or kennel cough. Meanwhile, the condition gradually worsens. - The importance of early diagnosis: The earlier the disease is detected, the better the treatment outcomes, and the more likely it is to prevent serious complications. - Risk of complications: If left untreated, lungworm disease can lead to life-threatening conditions such as pulmonary hemorrhage and pulmonary artery thrombosis. - Key warning signs: If your pet experiences chronic coughing, reluctance to exercise, or difficulty breathing for more than two weeks, it may not be just a cold. A veterinary check-up is recommended.

Types of Lungworms and Transmission Routes — How Does Infection Occur?

The most common types of lungworms are Angiostrongylus vasorum (French heartworm), Oslerus osleri (dog tracheal worm), and Crenosoma vulpis (fox lungworm). Angiostrongylus vasorum is characterized by its parasitism in the blood vessels of the lungs, specifically the pulmonary arteries. Infection typically occurs when dogs ingest intermediate hosts such as snails and slugs. The life cycle involves dogs coughing up first-stage larvae (L1) in their feces, which are then ingested by snails or slugs. The larvae develop within these mollusks, and infection is completed when the dog consumes the infected snail or slug. Transmission can also occur through accidental ingestion while grazing on grass or via paratenic (transport) hosts such as frogs or birds. Dogs that frequently walk in yards or parks are at particularly high risk of exposure.

Checklist of Main Symptoms of Dog Lungworm Infection

If two or more of the following symptoms persist for over two weeks, lungworm infection should be suspected.

Chronic cough: A wet cough that recurs for more than two weeks.

Exercise intolerance: Tiring quickly or becoming short of breath during walks.

Difficulty breathing: Rapid or labored breathing, even while at rest.

Loss of appetite and weight: Decreased energy and noticeable weight loss.

Nosebleeds or coughing up blood: Vascular lungworm disease can cause bleeding symptoms.

A lethargic dog lying down – Checklist for heartworm infection symptoms

Go to an Emergency Animal Hospital Immediately — Seek Care Now If These Symptoms Appear

If your pet shows severe difficulty breathing (panting with an open mouth), bluish gums or tongue (cyanosis), sudden decreased consciousness, or coughing up large amounts of blood, you must go to a 24-hour emergency animal hospital immediately. These symptoms can lead to pulmonary artery thrombosis or pulmonary hemorrhage, so time is of the essence.

How Is It Diagnosed? — Main Diagnostic Methods

- Fecal examination: The Baermann technique directly detects larvae in feces. To improve accuracy, it is best to collect and test samples over several consecutive days, such as three days in a row. - Thoracic imaging: X-rays and CT scans are used to identify lesions, nodules, and bronchoalveolar patterns within the lung tissue. These images help determine the extent of infection, particularly by observing changes in the caudal (rear) regions of the lungs. - Bronchoscopy: This procedure allows for direct visualization of parasites within the airways and is used as a complementary test when fecal examinations yield negative results. - Blood tests: These tests assist in diagnosis by detecting parasite proteins or DNA in blood or bronchoalveolar lavage fluid using ELISA or PCR, or by evaluating blood coagulation status. However, since neither blood nor fecal tests are perfect, treatment is sometimes initiated based on a presumptive diagnosis. - Recommendation for combined testing: Because single tests often miss the condition, it is generally necessary to perform two or three tests together to achieve an accurate diagnosis.

Treatment Methods — Step-by-Step Approach

- Step 1 — Deworming Medication: Your veterinarian will prescribe fenbendazole or ivermectin based on your puppy’s weight and the severity of the infection. It is essential to administer the medication consistently for the entire prescribed duration. - Step 2 — Symptom Relief: If breathing difficulties are present, oxygen therapy and bronchodilators are used together. In cases of severe lung inflammation, a short course of glucocorticoid (steroid) anti-inflammatory medication may also be prescribed. - Step 3 — Bleeding and Coagulation Management: Vascular lungworm disease can cause bleeding tendencies, such as nosebleeds or coughing up blood, due to blood clotting disorders. Rather than routinely using anticoagulants, your veterinarian will monitor coagulation status and carefully manage both bleeding and clotting risks based on clinical judgment. - Treatment Duration: The length of treatment varies depending on the severity of the infection but typically lasts from several weeks to about two months. Stopping medication prematurely on your own significantly increases the risk of recurrence. - Post-Treatment Testing: After completing the medication course, a follow-up test is essential to confirm that the larvae have been completely eliminated.

A veterinarian using a stethoscope to check the condition of the lungs at an animal hospital.

Care Points You Can Do at Home

- Ensure rest: During treatment, minimize strenuous activities like vigorous exercise or jumping, and allow your pet to rest adequately in a quiet indoor environment to promote faster recovery. - Adhere strictly to medication: It is most important to administer the prescribed dewormer completely for the entire specified duration; stopping the medication arbitrarily increases the risk of recurrence. - Dietary management: If your pet’s appetite decreases, switch to easily digestible, soft wet food and ensure they maintain adequate hydration. - Walk precautions: Avoid damp grassy areas and leaf litter where slugs and snails are commonly found, and prevent your pet from picking up or ingesting items from the ground. - Monitor symptoms: If coughing worsens or breathing becomes difficult during treatment, contact your veterinarian immediately.

A puppy resting at home to recover, along with its owner

Preventing Recurrence and Prevention — Remember This

Be sure to ask your veterinarian whether your dog’s regular deworming program includes protection against lungworms, as many standard heartworm preventatives do not cover them. In areas where lungworms are common, your vet may even recommend preventive deworming for puppies. Regular fecal exams can help confirm whether your dog is infected. To reduce the risk of reinfection, limit your dog’s contact with slugs and snails, promptly clean up feces, and avoid leaving food bowls outdoors.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently Asked Questions About Dog Lungworm Infection

Can heartworm infection be transmitted to humans?

Direct transmission to humans is extremely rare. However, since infection can occur through intermediate hosts such as snails, it’s essential to wash your hands thoroughly after handling your dog’s feces as a basic hygiene practice.

Can general dewormers treat lungworms?

Standard heartworm preventatives or over-the-counter dewormers may not fully eliminate lungworms. It is essential to have your pet diagnosed by a veterinarian and prescribed a dewormer containing ingredients specifically effective against lungworms.

Can heartworm infection be completely cured?

With early detection and appropriate deworming treatment, a full recovery is possible. However, for species that affect the pulmonary arteries, such as Angiostrongylus vasorum (French heartworm), the treatment course may be longer, and severe cases can result in lasting complications.

Is there a vaccine to prevent heartworm disease?

There is no specific vaccine for heartworm. The most effective prevention is maintaining a regular deworming program and ensuring your pet doesn't come into contact with slugs or snails during outdoor activities.

Can dogs raised in urban areas also contract heartworm disease?

Yes, slugs can be found in urban parks and even in apartment flower beds. Even city dogs need to be watched carefully during walks to prevent them from putting slugs or snails in their mouths while playing in the grass.

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References

[1] Bowman, D.D., Georgis' Parasitology for Veterinarians, 10th Ed, Elsevier, 2014

[2] Koch, J. & Willesen, J.L., Canine pulmonary angiostrongylosis: An update, Veterinary Journal, 2009

[3] Ettinger, S.J. et al., Clinical Medicine of the Dog and Cat, 4th Ed, Wiley-Blackwell, 2023

[4] Villiers, E. & Ristic, J., Notes on Canine Internal Medicine, 4th Ed, Wiley-Blackwell, 2016