Aelurostrongylus abstrusus is the cat lungworm — a parasitic roundworm that migrates to the small airways and causes chronic coughing, wheezing, and exercise intolerance that can be mistaken for feline asthma. It is acquired from eating infected prey and is more common than many cat owners realize.
Last reviewed: June 2026
What Is Cat Lungworm and How Do Cats Get Infected?
Aelurostrongylus abstrusus is a metastrongyloid nematode that completes its life cycle in the lungs of cats. Adult worms live in the terminal bronchioles and alveolar ducts, where females deposit eggs that hatch into first-stage larvae; the larvae are coughed up, swallowed, and shed in feces. Cats acquire the infection by eating the intermediate host — usually a terrestrial snail or slug — or by eating a paratenic host (bird, frog, or small rodent) that has itself eaten an infected mollusk. Outdoor and indoor-outdoor cats that hunt are at highest risk, though slug ingestion can occur even in cats with limited outdoor access.
As described in Tilley's 5-Minute Veterinary Consult, lungworm infections range in severity from subclinical to life-threatening interstitial pneumonia in heavy infestations, particularly in young or immunocompromised cats.
Recognizing Lungworm Infection Signs
Signs reflect the degree of larval and worm burden in the lungs and the inflammatory response they provoke.
Respiratory signs:
- Chronic cough — often intermittent at first, then persistent; may be mistaken for hairballs or asthma
- Wheezing or crackles audible on gentle chest compression
- Increased respiratory rate (normal resting rate for cats is 20–30 breaths per minute)
- Exercise intolerance — reluctance to run, play, or jump
- Open-mouth breathing in severe cases
Systemic signs:
- Weight loss despite reasonable appetite
- Reduced energy and increased sleep
- Runny eyes or nasal discharge in some cats
Many cats with mild to moderate infections cough only occasionally and appear otherwise well, making the diagnosis easy to miss without specific testing. Heavy infestations in kittens or elderly cats can cause rapid respiratory decline.
Traversa et al., 2008, Parasitology Research documented the epidemiology and clinical presentation of feline aelurostrongylosis across European cat populations, establishing that chronic cough is the most consistent presenting sign and that infections are frequently underdiagnosed due to reliance on auscultation alone.
How Vets Diagnose Feline Aelurostrongylosis
Diagnosis requires demonstrating larvae or adults in a suitable specimen.
Diagnostic approach:
- Baermann fecal technique — concentrates first-stage larvae from fresh feces; multiple samples over 3–5 days improve sensitivity because larval shedding is intermittent
- Bronchoalveolar lavage (BAL) — retrieves larvae and eosinophils directly from the airway; most sensitive when fecal methods are negative despite strong clinical suspicion
- Thoracic radiographs — may show a diffuse bronchial or alveolar pattern, sometimes with nodular opacities; cannot differentiate from asthma or other parasitic pneumonias on radiographs alone
- Complete blood count — peripheral eosinophilia supports a parasitic etiology but is not specific
Treatment and Prognosis
Lungworm infection is treatable with antiparasitic medications, and most cats recover fully.
Standard treatment options:
- Fenbendazole (oral, several weeks) — well tolerated and effective; as described in Plumb's Veterinary Drug Handbook, dosing is weight-based and typically continued for 14–28 days
- Selamectin, imidacloprid/moxidectin (spot-on) — registered for lungworm treatment in many countries and convenient for cats that resist oral dosing
- Supportive care — bronchodilators or short-course steroids may be added for cats with significant airway inflammation
Prognosis is excellent for otherwise healthy cats treated before severe lung damage occurs. Cats with heavy parasite burdens and acute respiratory distress have a more guarded prognosis and may require hospitalization and oxygen support.
When to See a Vet
Call your vet today if:
- Your cat has been coughing for more than one to two weeks with no improvement
- Your cat wheezes or you can hear breath sounds from across the room
- Your cat hunts regularly and has developed any new respiratory sign
- Your cat seems less willing to exercise, tires quickly, or is losing weight
Go to the ER immediately if:
- Your cat is breathing rapidly at rest (more than 40 breaths per minute)
- Your cat is breathing with mouth open or gums look pale, blue, or grey
- Your cat is sitting crouched with elbows held out — a sign of respiratory distress
What's going on with your pet?
Describe symptoms or snap a photo. Voyage tells you urgency, home care, and whether you need a vet.
First, tell us about your pet
Breed and age make a real difference in how Voyage interprets symptoms.
Describe the symptoms
Love it? See everything Voyage can do
Frequently Asked Questions
Can indoor cats get lungworm? Strictly indoor cats rarely get lungworm but are not entirely protected — accidental slug or snail ingestion can happen when cats chew on potted plants whose soil has been outdoors, or on houseplants. Hunting cats and outdoor cats face by far the greatest risk. If your indoor cat develops a persistent cough and you are not sure of its exposure history, mention the possibility of parasites to your vet.
How is cat lungworm different from asthma? Both cause chronic coughing and wheezing, and thoracic X-rays can look similar. Key differences: lungworm is caused by a live parasite and requires antiparasitic treatment, while asthma is an inflammatory airway disease managed with bronchodilators and steroids. Fecal Baermann testing or BAL cytology (showing larvae) distinguishes them. Some cats have both conditions simultaneously.
Is cat lungworm contagious to people or dogs? Aelurostrongylus abstrusus infects only cats — it does not infect people or dogs. The dog lungworm, Angiostrongylus vasorum, is a separate parasite. Routine handwashing after handling litter is always recommended as a general hygiene measure but is not required due to any human risk from this specific parasite.
How much does lungworm treatment cost? Vet exam and fecal Baermann testing typically run $80–200. Chest X-rays, if needed, add $150–350. Antiparasitic medication for a full treatment course generally costs $30–80. If BAL is required for diagnosis or the cat needs hospitalization for respiratory distress, total costs may reach $600–1,500 or more.
How do I prevent my cat from getting lungworm? Monthly application of a broad-spectrum parasite preventive that covers lungworm — such as selamectin or imidacloprid/moxidectin — dramatically reduces risk; the AAFP-AAHA Feline Life Stage Guidelines, 2021 recommend year-round parasite prevention for all cats at risk of outdoor exposure. Keeping cats indoors or limiting unsupervised hunting eliminates the primary exposure route. There is no vaccine against A. abstrusus.
Still Not Sure if Your Cat Needs a Vet?
When you're not sure if this is wait-and-see or call-tonight, Voyage AI Vet triages in under 2 minutes. Describe what you're seeing in chat, share photos or a short video of your cat coughing, breathing posture, or any wheezing sounds, or hop on a live video call if you want a second pair of eyes. Every answer comes with citations to the actual veterinary literature it's pulling from — so you see exactly where the guidance comes from, not just a chatbot's word.