When to see a vet urgently
Do not try to treat breathing difficulties at home with a wormer. Immediate help is needed if:
- your cat breathes with its mouth open or uses clear abdominal effort to breathe;
- the gums or tongue turn bluish or grey;
- your cat collapses, is very weak or cannot find a position that makes breathing easier.
Handle your cat calmly and contact an emergency practice: find a vet near you.
Overview
The cause is the nematode Aelurostrongylus abstrusus, for which the cat is the definitive host. Its life cycle includes intermediate hosts, slugs and snails, and optional transport hosts such as birds, rodents, frogs and lizards that may ingest larvae. A cat becomes infected by eating an intermediate or transport host. Larvae travel through the bloodstream to the lungs, where they develop into adult worms. This creates areas of respiratory inflammation that impair normal breathing.
A nematode is a roundworm. Adult worms live in small airways and alveolar ducts. Larvae released from eggs travel up the airways, are swallowed and pass into the faeces. Finding larvae in faeces therefore does not mean the main damage is in the intestine.
In a transport, or paratenic, host, infective larvae survive and pass to the cat in prey. A cat does not need to be seen eating slugs or snails to become infected. Not having observed hunting does not rule out exposure in a free-roaming cat either.
Causes
The main routes of lungworm infection are:
- eating infected slugs and snails;
- hunting small rodents, birds and amphibians that act as transport hosts;
- rarely, ingesting larvae in contaminated food or water.
The possible role of contaminated water or food is less certain than eating slugs, snails and prey. Infective larvae entering water has been demonstrated experimentally, but the frequency of this route in nature is unknown. Aelurostrongylus abstrusus does not usually pass directly between cats sharing a living space, as its life cycle needs an intermediate host.
Risk factors
- Free roaming and hunting wildlife.
- Living in endemic areas where the parasite is common.
- Young cats, with kittens affected more often.
- A weakened immune system, increasing susceptibility to parasitic disease.
The best-recognised exposure factors concern outdoor access, hunting and the local parasite situation. Less is known in cats about the independent role of reduced immunity specifically in acquiring this infection. Adult cats can become infected too. Tell the vet about previous countries of residence and travel as well as the current home, because parasite distribution varies by region.
Main symptoms
Symptoms depend on the intensity of infection:
- chronic coughing that worsens with exertion;
- breathlessness and rapid breathing;
- exercise intolerance and tiring quickly;
- crackling or wheezing breathing sounds;
- blue mucous membranes, or cyanosis, weight loss and exhaustion in severe cases.
- Some cats have no symptoms, but parasites continue to damage lung tissue.
A coughing cat may crouch low and extend its neck. An episode may end in gagging, making it look like an attempt to vomit a hairball. Repeated coughing without a hairball is nevertheless a respiratory sign whose cause needs investigation. A short video taken in calm circumstances may help show the practice what happened at home; filming must not delay departure when breathing is difficult.
Cough severity alone does not show how badly the lungs are damaged. Lungworm infection may cause no symptoms or only mild coughing, but some cats develop significant breathing difficulties. Asthma, other respiratory inflammation and chest cavity disease can look similar. A parasite medicine or asthma treatment is therefore not selected from a single sound or breathing pattern.
Complications and consequences
Without treatment, aelurostrongylosis can lead to:
- chronic bronchitis;
- inflammation and fibrosis of lung tissue;
- severe respiratory failure;
- secondary respiratory infections;
- death from suffocation in extreme cases.
Not every infection results in severe disease. Prognosis depends on the extent of lung changes, the cat's condition and starting treatment. Severe respiratory illness is a particular concern in small kittens. Cats also have several lungworm species, sometimes together: not every lungworm risk or transmission route applies specifically to Aelurostrongylus abstrusus.
Diagnosis at the vet
Diagnosis is based on:
- faecal testing by the Baermann method, which detects larvae that ordinary flotation is unlikely to reveal; collecting samples over three days is useful, and PCR is also possible;
- bronchoalveolar lavage and microscopy;
- chest X-rays showing typical infiltrates and lung nodules;
- a complete blood count, with eosinophilia suggesting parasitic infection.
The Baermann test uses live larvae moving out of a faecal sample. An ordinary faecal examination may not include this method, so the request needs to mention suspected lungworm. Collect samples as instructed by the practice and report previous parasite treatments. Sample freshness and collection method affect success.
One negative sample does not rule out infection. Initially, larvae are not yet shed in faeces, and later shedding may be intermittent or low. Testing may be repeated or supplemented with another method. Larvae must also be distinguished from similar-looking lungworm species because the parasite identified affects interpretation and treatment.
Bronchoalveolar lavage means collecting a wash sample from the bronchi and alveoli. It is not automatically needed to find the parasite, and sampling may place strain on a cat with breathing difficulties. A lavage sample without visible larvae does not alone rule out aelurostrongylosis. Increased eosinophils, a type of white blood cell, are not a specific confirmation of this parasite either.
X-rays show lung changes and their extent, but other causes can produce similar changes. Blood oxygenation may also be assessed. If your cat is breathing poorly, the vet may start oxygen and stabilise it before broader investigations. Collecting faecal samples must not delay veterinary treatment for a cat struggling to breathe.
Treatment and monitoring recovery
Confirmed infection is treated with a parasite medicine suitable for cats, selected by the vet. The choice considers parasite species, age, weight and the product's licensed use. Treatment is not determined simply by the word “wormer” on a pack. The vet also assesses whether treatment beyond parasite removal is needed for lung inflammation or a confirmed bacterial complication.
A severely ill cat may need hospital care and oxygen. Antibiotics do not kill roundworms, and a cough improving during antibiotics does not prove the infection has cleared. Equally, worming does not replace investigation of other respiratory disease if symptoms persist. The vet plans follow-up and any faecal tests needed to confirm response.
Breathing symptoms may worsen early in treatment because of inflammation triggered by dying parasites. Do not interpret worsening breathing at home as an expected, harmless adverse effect; the cat needs reassessment. Keep a recovering cat indoors and monitor resting breathing, appetite and energy. Lung recovery and the end of larval shedding do not necessarily occur at exactly the same time.
Prevention
- Limit free roaming and hunting wildlife.
- In line with ESCCAP guidance, hunting cats are treated with products shown to work against lungworms, such as moxidectin or emodepside; ordinary wormers do not work against them.
- Control your cat's access to slugs, snails and possible intermediate hosts.
- Maintain food hygiene and do not feed raw prey animals.
The point about ordinary wormers means that the effectiveness of any parasite medicine cannot be assumed. Some active ingredients also used for other worming purposes work against lungworms, but the product and method of use are chosen separately. Preventive needs depend on local distribution and hunting; there is no single worming programme for every country or every cat.
Reinfection is possible if hunting continues after treatment. A secure outdoor enclosure or other supervised outdoor access reduces opportunities to eat intermediate hosts and infected prey. Tell the vet about changes in outdoor access so prevention matches actual exposure.
What it means for owners
Aelurostrongylosis is a dangerous parasitic disease that can remain hidden for a long time and cause serious respiratory damage. Remember that parasites can cause coughing and signs resembling bronchitis or asthma. Early diagnosis and timely treatment prevent chronic respiratory failure and significantly improve quality of life.
Starting treatment early improves the chance of recovery, but complete repair of existing lung damage cannot be promised. If coughing continues or breathing becomes laboured again, your cat needs reassessment even after parasite treatment has been completed.
Please note: this material provides general information and does not replace treatment advice. Contact a vet if you notice the first symptoms.
Frequently asked questions
Can an indoor cat have lungworm?
Living indoors now does not rule out a previous infection acquired outdoors or through hunting. A symptomatic cat's history is therefore reviewed. Risk in a wholly indoor cat is assessed according to actual opportunities for exposure.
Why did an ordinary faecal test not find the parasite?
Not every faecal test includes the Baermann method, and larval shedding varies. Larvae are not yet present in faeces early in infection. The vet may therefore recommend another sample or an additional test.
Can this lungworm infect people?
Aelurostrongylus abstrusus is not known to pose a human infection risk. However, not all feline respiratory parasite species are the same. Good hand hygiene and appropriate removal of faeces are part of animal care regardless of diagnosis.
This article is for general information only and is not a guide to treatment. If you notice the first signs of illness, contact your vet.
Paw4care editorial team
Sources
- Guideline for Lungworm Disease, ABCD, accessed 2026-11-03.
- Worm Control in Dogs and Cats: Guideline 01, Seventh Edition, June 2025, ESCCAP, accessed 2026-11-03.
- Aelurostrongylus abstrusus, Companion Animal Parasite Council, accessed 2026-11-03.
- Lungworm Infection in Cats, MSD Veterinary Manual, accessed 2026-11-03.
- Dyspnea: Difficulty Breathing, Cornell Feline Health Centre, accessed 2026-11-03.
- Breathing Problems in Cats, PDSA, accessed 2026-11-03.
- Coughing in Cats, VCA Animal Hospitals, accessed 2026-11-03.
- Introduction to Lung and Airway Disorders of Cats, MSD Veterinary Manual, accessed 2026-11-03.
- Evaluation of Bronchoscopy and Bronchoalveolar Lavage Findings in Cats With Aelurostrongylus abstrusus in Comparison to Cats With Feline Bronchial Disease, Frontiers in Veterinary Science, accessed 2026-11-03.