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Lungworms: The Cough Explained
The slug and snail connection every outdoor cat owner should know.
Last reviewed
The slug and snail connection every outdoor cat owner should know.
Last reviewed
Most worms live in the gut. Lungworm larvae migrate to the airways instead, where they set up home in the small passages of the lungs and make themselves known through the breathing.
The route in is pure garden food chain: larvae live in slugs and snails, cats catch it by eating them directly, or far more often by eating the birds, rodents and frogs that ate them first. Which is why lungworm is overwhelmingly a condition of hunters and confident outdoor cats, and why indoor and catio life quietly protects against it.
The signature is a persistent cough, sometimes with wheezing, faster breathing at rest, or breathlessness after mild play, in a cat that seems otherwise fairly well. Heavy burdens add weight loss and lethargy; kittens and young hunters tend to show the most.
A cat cough is easy to mistake for hairballs in reverse: hairball effort ends in a delivery, a lungworm cough just keeps happening. Any cough that persists beyond a few days, or any change in resting breathing, earns a vet visit regardless of cause.
Vets diagnose lungworm from the story, a chest listen, sometimes stool tests that catch larvae, and occasionally imaging. Treatment is effective: specific prescription wormers clear it, though the airways can take a little while to settle afterwards.
Prevention is refreshingly simple. Some monthly prescription parasite products cover lungworm as standard, worth requesting for any dedicated hunter, and the slug pellet warning belongs here too: metaldehyde pellets are dangerously toxic to cats, a second reason to keep them out of your garden.
Adult lungworms live in the airways and lay eggs that hatch on the spot; the larvae are coughed up, swallowed, and leave in the stools, where slugs and snails collect them. Frogs, birds and rodents eat the molluscs, cats eat the middlemen, and the larvae migrate from gut to lungs to begin again.
The whole tour, cat to cat, takes about six weeks, and every link is outdoors. Cut any link, no hunting, no slug snacks, and the cycle simply cannot reach an individual cat, which is the quiet logic behind the catio’s protection.
Lungworm sheds larvae into stools intermittently, so a single clear sample proves very little, and the standard flotation test used for other worms misses it entirely; the lab needs a specific technique and ideally samples pooled across days. X rays show changes that mimic asthma and infection.
Because of all this, vets sometimes reach the diagnosis by treating for it: a specific wormer course, then watching whether the cough dissolves. If your outdoor hunter has a stubborn cough and tests keep coming back unhelpful, asking about lungworm by name is a genuinely useful contribution.
List what reaches a cat through hunting and grazing the garden food chain: lungworm, most tapeworm, toxoplasma, a share of the roundworm burden, and the slug pellet risk beside them. Catio and indoor living cancels the lot in one design decision, without a single dose of anything.
This is not an argument that outdoor cats are doing it wrong; it is the honest accounting behind why our own cats have supervised outside time and screened runs instead of the open food chain. Prevention by architecture is the cheapest medicine there is.
A chronic cough in a cat gets blamed on hairballs first and asthma second, and lungworm hides comfortably behind both: the retching cough that never produces a hairball, the wheeze that comes and goes, the cat slightly slower up the stairs. The imitation is good enough to fool households for months.
The tell is persistence plus lifestyle: a coughing cat that hunts or patrols a garden has earned the lungworm question by default. Say the word at the consult; it moves the parasite from afterthought to tested for, and testing is where this diagnosis is won.
The parasite travels through slugs and snails, and cats rarely eat those on purpose: the routes in are the hunted mouse or bird that ate the mollusc first, grooming after contact with slime trails, and drinking from outdoor water where slugs have cruised the rim overnight.
That map writes the prevention: water bowls in catios lifted or covered at night and rinsed each morning, toys and food never left out in slug country after dark, and the committed hunter acknowledged as the risk carrier he is. You cannot fence out molluscs; you can stop laying the table for them.
Many lungworm infections are quiet, a light worm burden that a healthy adult carries with a cough or with nothing at all, and some clear on their own. The serious end belongs to kittens, the elderly and the heavily infected, where inflammation narrows airways and breathing becomes genuine work.
The escalation signs read like any breathing emergency: effortful or open mouth breathing, blue tinged gums, exhaustion after nothing. Those belong to the same day and phone ahead category regardless of suspected cause, with the lungworm history offered on arrival.
Treatment is straightforward once the worm is named: specific antiparasitics from your vet, sometimes with support for the airway inflammation, and a recheck that may repeat testing to confirm the lungs are clearing. Coughs can outlast the worms briefly while irritation settles.
Staying clear afterwards is a products conversation: several routine parasite treatments cover lungworm and several do not, so the hunting cat’s prevention plan deserves an explicit yes it covers lungworm from your vet rather than an assumption from a supermarket box.
Lungworm is the worm at the wrong address: larvae swallowed with prey or slugs and snails mature in the lungs, producing a chronic cough, wheeze or breathlessness that imitates hairballs and asthma. Hunters and outdoor cats carry the risk; indoor life is a genuine dividend. Diagnosis is slippery and may take repeated tests, treatment is specific prescription wormers rather than every product on the shelf, and a coughing cat that never produces a hairball has earned the vet conversation.
Rarely: the cycle needs molluscs or prey, which pure indoor life largely excludes. A catio blurs the line slightly, which is why bowl hygiene and the slug map matter for catio households.
Not directly: an infected cat sheds larvae that need the mollusc detour before they can infect anyone else. Housemates share risk factors rather than the infection itself, so the hunter’s diagnosis is the indoor cat’s reassurance.
Usually by finding larvae in stool samples, often needing samples across several days because shedding fluctuates, sometimes supported by chest imaging. A negative single sample in a coughing outdoor cat is a reason to persist, not to close the file.
Heavy untreated burdens can, particularly in kittens and frail cats, though most cases caught and treated do fully well. The disease’s real danger is the months it spends misfiled as hairballs.
Only if the specific product does: standard intestinal wormers do not all reach lungworm. Check the actual product with your vet rather than assuming the word wormer covers everything.
Dogs have their own species with its own drama; the feline version is a different parasite with a similar mollusc detour. The prevention habits overlap, the products and stakes differ, and each species needs its own plan.
Possibly a light burden self resolving, possibly a pause: lungworm coughs wax and wane. A stool check costs little and settles it properly, especially for a cat who will keep hunting.
Hunters collect tapeworm from the same menu, so read the tapeworm guide alongside this, and our catio guide shows outdoor life without the food chain.
To read further on lungworm, ESCCAP tracks its spread across Europe with maps, and International Cat Care explains diagnosis and treatment for owners. See the culprit itself: the Aelurostrongylus abstrusus page carries the science and the pictures.