Lungworm in cats is a parasitic infection caused by tiny roundworms that live inside the airways and lung tissue. The most common species, Aelurostrongylus abstrusus, is found worldwide and is often called “the cat lungworm.” Infections range from completely silent to life-threatening, depending on how many worms are present and how old or healthy the cat is.
The Parasites Behind It
Three main species cause lungworm disease in cats. Aelurostrongylus abstrusus is by far the most common. It burrows into the tiny air sacs deep in the lungs. A second species, Troglostrongylus brevior, lives higher up in the bronchial tubes and has so far been documented mainly in Southern and Eastern Europe and the Middle East. The third, Capillaria aerophila, has a worldwide distribution and can infect many carnivore species, not just cats.
A handful of rarer species exist, but they show up so infrequently that their role in real-world feline disease is still unclear.
How Cats Get Infected
Cats don’t pick up lungworm directly from other cats. The parasites need an intermediate host to develop, and that host is almost always a snail or slug. An infected cat coughs up larvae, swallows them, and passes them in feces. Snails and slugs pick up the larvae from contaminated soil. Inside the mollusk, the larvae mature into a form that can infect a new cat.
Most cats don’t deliberately eat snails, though. More often, they catch a mouse, rat, lizard, frog, or bird that has already eaten an infected snail. These animals serve as “paratenic” or transport hosts, carrying the larvae in their tissues without being affected themselves. Research has confirmed lungworm DNA in rats, geckos, and various other small prey animals collected from ordinary garden environments. For outdoor and hunting cats, every small creature they catch is a potential source of infection.
There is also evidence that Troglostrongylus brevior can pass from a mother cat to her kittens through milk, which helps explain why very young kittens sometimes develop severe disease before they’ve had a chance to hunt.
Signs and Symptoms
Many cats with lungworm show no symptoms at all. Subclinical infections are common, especially in adult cats with a low worm burden and a healthy immune system. When signs do appear, they typically involve the respiratory system: a persistent cough, wheezing, sneezing, nasal discharge, or labored breathing. Some cats breathe faster than normal at rest or become less tolerant of exercise.
Severity depends heavily on worm burden, age, and the cat’s overall health. Kittens and young cats are at the highest risk for serious illness. Fatal pneumonia has been documented in kittens as young as two months old. One case report describes irreversible pulmonary hypertension (dangerously high blood pressure in the lungs) in a kitten infected with T. brevior, even after appropriate treatment was given. In adult cats, severe cases can cause secondary bacterial infections in the lungs, weight loss, and general decline, but fatal outcomes are much less common.
How Widespread Is It?
Lungworm is found on every continent where cats live. Prevalence varies enormously by region and lifestyle. In Europe, reported infection rates for A. abstrusus range from less than 1% to over 43%, depending on the country and the population studied. Italy is a known hotspot, with prevalence reaching up to 38% in some areas. Parts of Spain have seen rates climb from the traditional 1–2% to as high as 55% in recent surveys.
Stray and colony cats are far more likely to be infected than owned indoor cats. One study found A. abstrusus in 34.5% of street colony cats compared to just 3.3% of cats in shelters. Owned cats that stay indoors had zero infections in the same study. The trend across Europe is upward: researchers believe prevalence has been increasing in recent decades, possibly because of expanding snail populations, growing stray cat numbers, or simply better diagnostic awareness.
Cases are also reported in Asia, the Americas, and Australia, though large-scale prevalence data outside Europe is sparser.
Diagnosis
Lungworm is often missed because routine fecal tests designed for intestinal parasites won’t catch it. The standard diagnostic method is a specialized test called the Baermann technique, which uses gravity and warm water to coax larvae out of a fresh stool sample. It’s considered the gold standard, but its sensitivity tops out around 90%, meaning it can still miss some infections. False negatives are especially likely if the cat has a light worm burden or if the larvae aren’t being shed consistently.
Chest X-rays can show characteristic patterns of lung inflammation, but they aren’t specific enough to confirm lungworm on their own. In difficult cases, vets may use a pharyngeal swab (a swab from the back of the throat) combined with molecular testing (PCR), which has shown sensitivity comparable to the Baermann method. The key challenge is that many infections are subclinical, so there’s nothing prompting the owner to bring the cat in for testing in the first place.
Treatment Options
Lungworm responds well to antiparasitic medications when caught in time. Treatment generally falls into two categories: an oral deworming paste given over several days, or a topical spot-on solution applied to the skin on the back of the neck.
Spot-on formulations containing moxidectin have shown the strongest results in clinical trials, achieving 100% clearance of A. abstrusus after 30 days in one study. Some cats need more than one round. In a case series of naturally infected cats treated with a moxidectin-based spot-on, four out of seven still tested positive at a two-week recheck and needed retreating. By day 50, all cats had two consecutive negative fecal tests. Other spot-on products containing eprinomectin or emodepside have also proven effective against A. abstrusus and, in some reports, against T. brevior and C. aerophila as well.
Oral deworming paste is typically given once daily for three days. It’s effective but may be harder to administer to uncooperative cats compared to a spot-on. Your vet will choose the approach based on the specific parasite involved, the severity of the infection, and what products are available in your region.
Supportive care matters too. Cats with secondary bacterial infections may need antibiotics. Those with severe breathing difficulty could need oxygen therapy or anti-inflammatory medication to reduce lung swelling while the antiparasitic drugs take effect.
Long-Term Outlook
Most adult cats recover fully once the worms are eliminated. Mild infections often resolve without lasting damage to the lungs. The picture is more concerning for kittens, where infection can lead to fatal respiratory failure even with treatment. Permanent lung scarring and irreversible pulmonary hypertension have been documented in young cats with heavy infections, particularly those caused by T. brevior.
Reinfection is possible since surviving lungworm doesn’t appear to grant lasting immunity. Cats that continue to hunt are at ongoing risk.
Prevention
Keeping cats indoors eliminates exposure to infected prey and intermediate hosts. For cats that go outside or hunt, regular use of a broad-spectrum antiparasitic that covers lungworm is the most practical protection. Several monthly spot-on products marketed for flea, tick, and worm prevention also have documented activity against lungworm species. Moxidectin-based and eprinomectin-based formulations have the strongest evidence for both preventing and treating feline lungworm infections. Milbemycin oxime, given orally, has also shown effectiveness in individual cases.
Not all standard dewormers cover lungworm. Products designed only for roundworms and tapeworms won’t help. If your cat spends time outdoors, it’s worth confirming with your vet that their parasite prevention program specifically includes lungworm coverage, especially if you live in an area where the parasite is common.