Lungworm in cats: signs, risks and prevention

Lungworm sounds alarming, and it's natural to want to understand it properly rather than just worry about it. The good news is that most cats who pick up lungworm show mild signs, or none at all, and the parasite responds well to treatment once it's identified. The tricky part is that lungworm can look like several other, more common problems, so knowing what to watch for helps you get your cat seen sooner rather than later.

This guide explains what lungworm actually is, how cats catch it, the signs to look out for, and what your vet will do to diagnose and treat it. We've drawn on veterinary and charity sources to keep this accurate, because guesswork isn't good enough when it comes to your cat's lungs.

Outdoor cats, keen hunters, and kittens tend to carry the highest risk, but any cat that goes outside — or even one that stays in but shares a home with a hunting housemate — can be exposed. Understanding the risk factors is the first step to managing them sensibly.

What is lungworm in cats

"Lungworm" isn't one single parasite — it's a term used for several different worms that can end up living in a cat's airways or lung tissue. The one vets see most often in cats is called Aelurostrongylus abstrusus, sometimes just referred to as the cat lungworm. According to a peer-reviewed veterinary guideline published via the European Advisory Board on Cat Diseases (ABCD), this species is "the most prevalent in domestic cats" worldwide, living in the small airways and lung tissue once it matures.

Other, rarer worms can also affect the feline respiratory tract, including *Troglostrongylus brevior* and *Capillaria (Eucoleus) aerophila*. These are less common in the UK but are being recognised more often by vets, partly thanks to better diagnostic testing. It's worth knowing they exist, but *Aelurostrongylus abstrusus* remains the one most UK cats are actually exposed to.

It's also worth clearing up a common confusion: cat lungworm is a different parasite from the lungworm that affects dogs (*Angiostrongylus vasorum*). Cats Protection confirms this distinction directly, noting that the common feline lungworm cannot pass to humans, and that dogs cannot catch it from cats either. A rarer worm, *Capillaria aerophila*, is one of the few that can pass between cats and dogs, but this isn't the "classic" lungworm most owners have heard of.

How cats catch lungworm

Cat lungworm has an indirect life cycle, which means it needs to pass through another creature before it can reach your cat. Slugs and snails act as the main intermediate host. The worm's larvae develop inside these gastropods, and cats become infected either by eating an infected slug or snail directly, or — far more commonly — by eating a "paratenic" host that has itself eaten an infected slug or snail.

Paratenic hosts include small birds, mice, frogs, and lizards. VCA Animal Hospitals explains that cats typically become infected "by eating slugs or snails, or by eating another animal that has eaten a slug or snail, such as a snake, lizard, mouse, or bird." This is why keen hunters are so much more likely to pick up the parasite than cats who don't hunt at all.

Once swallowed, the larvae travel through the gut wall, into the bloodstream, and eventually to the lungs, where they mature into adult worms over several weeks. Adult females lay eggs in the lung tissue; these hatch into first-stage larvae, which the cat coughs up, swallows, and passes out in their faeces — ready to be picked up by another slug or snail, continuing the cycle.

Cats Protection also notes that cats can occasionally pick up lungworm from drinking water contaminated with larvae, although hunting prey remains the far more typical route of infection. Indoor-only cats that never hunt are at very low risk, but not quite zero, particularly if slugs or snails ever find their way indoors or into a garden the cat has access to.

Which cats are most at risk

Any cat that hunts is at higher risk, but a few groups deserve particular attention:

• Outdoor and semi-outdoor cats who roam gardens, farmland, or anywhere with slug and snail populations.
• Confident hunters, especially cats who regularly bring home birds, mice, or amphibians.
• Kittens, whose immune systems and airways are still developing. The ABCD guideline notes that infection has been documented in kittens as young as eight weeks old, and that vertical transmission from a queen to her kittens (via the placenta or milk) "cannot be excluded" as a route of infection — meaning kittens can, in principle, be born with or acquire the parasite very early in life.
• Cats living in multi-cat, semi-rural, or rescue environments where hunting and outdoor access are more common and worming history may be unknown.

Kittens and older cats tend to show more obvious clinical signs than fit, healthy adults, because smaller airways and less mature or less robust immune responses make the effects of even a modest worm burden more noticeable.

Signs and symptoms to watch for

This is where lungworm becomes genuinely tricky: a good number of infected cats show no symptoms at all, and the infection is sometimes only picked up incidentally when a vet is investigating something else entirely. When signs do appear, they're respiratory in nature and can look very similar to feline asthma, bronchitis, or a straightforward chest infection.

Signs reported by Cats Protection and VCA Animal Hospitals include:

• Coughing — often the most noticeable sign, sometimes persistent or worsening over time
• Rapid or laboured breathing, or audible wheezing
• Sneezing and nasal or eye discharge
• Reduced appetite or gradual weight loss
• Lethargy, playing less than usual
• Fever and, in some cases, swollen lymph nodes

In more severe or advanced cases, cats can develop marked breathing difficulty, and the peer-reviewed ABCD guideline warns that heavy infections can, in rare instances, progress to respiratory failure. This is uncommon, and most cats who receive appropriate treatment recover well, but it's precisely why persistent coughing or breathing changes in a cat should never simply be waited out at home.

A cat that "just has a cough" that doesn't clear up within a week or two is always worth a vet visit — coughing has several possible causes, and lungworm is only one of them, but ruling it in or out matters.

Because these signs overlap so heavily with other chest conditions, a second peer-reviewed review on feline lungworm diagnosis specifically flags that cats are sometimes treated for asthma with corticosteroids or bronchodilators, which can temporarily mask an underlying lungworm infection rather than resolve it. This is one of the main reasons proper diagnostic testing matters rather than assuming a diagnosis from symptoms alone.

How vets diagnose lungworm in cats

Diagnosing lungworm isn't always straightforward, because the larvae aren't shed constantly and some testing methods are more reliable than others. Vets typically use one or more of the following approaches:

Faecal testing (the Baermann technique)

The gold-standard test is the Baermann migration technique, which relies on the fact that live larvae move towards warmth and moisture, allowing them to be separated out from a fresh faecal sample and identified under a microscope. It's accurate but takes around 24 to 48 hours to run, and because larvae shedding can be intermittent, vets sometimes need to test more than one sample over a few days to be confident of a negative result.

Direct faecal smears

A simpler, quicker faecal smear or flotation test can be used, but the peer-reviewed literature is clear that these are considerably less reliable than the Baermann technique, since larvae can be damaged or missed using these quicker methods.

PCR (molecular) testing

Newer PCR-based tests look for the parasite's genetic material rather than the larvae themselves. A peer-reviewed review of feline lungworm diagnostics reports that PCR testing has demonstrated "a specificity of 100% and a sensitivity of ~97%" for detecting *Aelurostrongylus abstrusus*, and has successfully identified infected cats that tested negative on conventional microscopy. This makes PCR a valuable option where lungworm is suspected but faecal testing hasn't confirmed it.

Imaging and other tests

Chest X-rays can show thickening of the bronchial walls or small nodules in the lungs consistent with lungworm, though these changes aren't unique to lungworm and need to be interpreted alongside other test results. In cats with more severe disease, a vet may also recommend bloodwork or, less commonly, a bronchoalveolar lavage (a sample taken directly from the airways) to look for larvae.

Because no single test is perfect, your vet may use a combination of these methods, particularly if lungworm is suspected but an initial faecal sample comes back clear.

Treatment options

The reassuring news is that once lungworm is confirmed, treatment is generally straightforward and effective. Several antiparasitic medications are used, and your vet will choose based on your cat's age, health, and how the infection is confirmed. Options referenced across veterinary sources include:

• Fenbendazole paste, typically given once daily for several days
• Spot-on treatments combining ingredients such as moxidectin with imidacloprid, or emodepside with praziquantel
• Oral tablets combining milbemycin oxime with praziquantel
• Other prescription-only wormers selected by your vet based on the specific parasite species involved

Most cats with a mild to moderate infection improve within a few weeks of starting treatment, though your vet may continue treatment for longer to make sure all larval stages have been cleared, since a single dose doesn't always kill every life stage of the parasite. Cats with more severe respiratory signs, such as pneumonia caused by a heavy larval burden, sometimes need additional supportive care — this can include anti-inflammatory medication, and antibiotics if a secondary bacterial infection has taken hold. It's worth stressing that antibiotics alone cannot clear a worm infection; they only address secondary complications.

All of the medications used to treat lungworm are prescription-only, which means diagnosis and treatment always need to go through your vet rather than being self-selected from a shelf. If your cat is diagnosed with lungworm, your vet will also talk you through what to expect during recovery and whether any follow-up testing is needed to confirm the infection has cleared.

Prevention: reducing your cat's risk

You can't remove the risk of lungworm entirely if your cat goes outdoors and hunts, but there's a lot you can do to reduce it:

• Keep up with parasite prevention. Many modern monthly spot-on and oral parasite treatments cover lungworm alongside fleas and other worms — ask your vet which product is appropriate for your cat's age, weight, and lifestyle, and stick to a regular schedule rather than treating only occasionally.
• Reduce hunting opportunities where you can. Cats Protection suggests that keeping your cat entertained and well-exercised indoors, through regular play sessions, can reduce their motivation to hunt outside. A bored cat is often a more determined hunter.
• Discourage access to prey. If your cat regularly brings home dead or live birds, mice, or amphibians, consider a well-fitted bell on their collar (with a quick-release safety mechanism), or supervised outdoor time during dawn and dusk, when small prey is most active.
• Don't ignore a persistent cough, even a mild one. Catching lungworm early, before it causes significant lung changes, makes treatment easier and recovery faster.
• Keep fresh water available and avoid leaving standing water outside that could carry contamination, since drinking contaminated water is an occasional, if less common, route of infection.

There's currently no vaccine against feline lungworm, so prevention relies on a combination of regular parasite treatment, sensible hunting management, and staying alert to early signs — rather than any single measure doing all the work.

Common mistakes owners make

A few patterns come up again and again with lungworm, and they're worth knowing so you can avoid them:

• Assuming an indoor cat has zero risk. It's much lower, but not nil — slugs and snails occasionally make their way indoors, and even a strictly indoor cat can be exposed if a housemate cat hunts outside and brings prey home.
• Treating a cough as "just a hairball" for too long. A cough that persists for more than a week or two, or that's getting worse, deserves a vet check rather than continued watching and waiting.
• Stopping parasite prevention once a cat is treated. Recovering from one infection doesn't confer lasting immunity — cats can be reinfected if they continue hunting and aren't kept on a regular preventative schedule.
• Relying on a single faecal test to rule lungworm out. Because larvae shedding can be intermittent, one clear result doesn't always mean a cat is definitely free of the parasite, particularly if clinical suspicion remains high. Your vet may recommend repeat testing or PCR if symptoms persist.
• Confusing cat and dog lungworm. They're different parasites with different life cycles and different treatments, so information written for dog owners doesn't always transfer directly to cats.

When to see your vet

Book a vet appointment if your cat develops a cough that lasts more than a week, especially if it's worsening, or if you notice faster or laboured breathing, wheezing, reduced appetite, weight loss, or unusual lethargy. These signs have several possible causes besides lungworm, but your vet is best placed to work out which — and to start the right treatment quickly if it does turn out to be lungworm.

Seek urgent or emergency veterinary care if your cat is struggling to breathe, breathing with an open mouth, has blue-tinged gums, or seems distressed at rest. These are signs of a genuine emergency regardless of the underlying cause, and shouldn't wait for a routine appointment.

If your cat is a confident outdoor hunter, it's also worth mentioning this to your vet at routine check-ups so they can advise on the most appropriate ongoing parasite prevention for your cat's specific lifestyle, rather than a generic one-size-fits-all schedule.

*This is general guidance, not a substitute for advice from your vet, who can assess your individual pet.*

Sources

• Cats Protection — lungworm in cats: how it's caught, symptoms and treatment (cats.org.uk).
• VCA Animal Hospitals — lungworm infections in cats: transmission, diagnosis and treatment (vcahospitals.com).
• European Advisory Board on Cat Diseases (ABCD) guideline on lungworm disease in cats, peer-reviewed via PubMed Central (pmc.ncbi.nlm.nih.gov).
• Peer-reviewed review — diagnosis and management of lungworm infections in cats, PubMed Central (pmc.ncbi.nlm.nih.gov).