A dry cough that lasts 3 weeks in a cat is usually filed as asthma, and sometimes that is right. But a worm that lives in the small airways produces the same cough, the same wheeze and often a normal appetite, and it is confirmed with 2 tests rather than guessed at. The distinction matters because the treatments point in different directions, and one of them is a course of deworming rather than a lifetime of inhaled drugs.
What the worm does inside the cat
Adult worms live in the bronchioles and lay eggs that hatch into larvae about 350 to 400 micrometers long. Those larvae are coughed up, swallowed, and pass out in the stool, which is why a fecal test can find a lung disease. The prepatent period runs 4 to 6 weeks, so a cat infected on a hunting trip in June may cough in July and shed larvae only from August. Cats pick the worm up by eating an infected slug or snail, or a paratenic host such as a rodent, bird, lizard or frog that ate one first. Larvae also travel in slug slime, which is how an indoor cat with a potted plant gets infected without ever meeting a snail.
Outdoor access is the main risk factor, and the peak age is 1 to 8 years, though kittens under 6 months can pick it up in the first weeks outdoors and worsen faster than adults.
Three symptom groups, and what each looks like
Signs cluster in 3 groups, and a cat rarely shows all of them at once:
- Respiratory. A dry, hacking cough in 1 to 4 bouts a day, worse at night or after 10 minutes of play; a resting breathing rate of 40 to 60 breaths a minute against a normal 20 to 30; a wheeze you can hear from 30 cm away with the ear close to the chest.
- Body condition. Weight loss of 200 to 500 g over 4 to 8 weeks while the cat still eats; a pot-bellied look in kittens; a coat that turns dull; growth that stalls before 6 months.
- Digestive and general. Vomiting 1 or 2 times a week, soft stool, sneezing, and in heavy infections a sudden collapse within 24 to 48 hours, which is uncommon but is the reason a coughing kitten is not a wait-and-see case.
The trap is the cat that only coughs. Appetite stays normal, weight drifts down by 300 g over 2 months, and the owner assumes hairballs. Hairballs produce vomiting of a tube of hair, not a dry cough in bouts.
Two tests that settle the question
The first test looks for larvae, the second looks for their DNA. Doing both is reasonable when the first is negative and the cough continues.
| Test | Sample | Amount needed | Result in | Finds | Main limit |
|---|---|---|---|---|---|
| Baermann, 1 sample | Fresh feces | 5 to 10 g | 12 to 24 hours | Live larvae, 350 to 400 micrometers | Misses about 1 in 3 |
| Baermann, 3 samples over 3 days | Fresh feces | 15 to 30 g total | 3 to 4 days | Intermittent shedding | Needs 3 trips or a fridge |
| Fecal PCR | Feces | 0.5 to 1 g | 2 to 5 days | Worm DNA | Costs 2 to 3 times more |
| Airway wash | Saline from the lung | 2 to 5 ml | 24 to 48 hours | Larvae and cells | Needs sedation |
| X-ray | Chest image | 2 views | Same day | Bronchial pattern | Cannot confirm the worm |
A single Baermann test is the usual starting point because it is cheap and specific, but its sensitivity is the weak point: larvae are shed in waves, so one negative sample lowers your suspicion by less than owners expect. Three samples across 3 days, or a PCR alongside, is the practical answer when the cough has already lasted 3 weeks.
What the X-ray adds, and what it cannot say
Chest films in an infected cat often show a bronchial pattern, sometimes a nodular one, with no fluid and a normal heart silhouette. Those changes overlap with asthma, bronchitis and early heart disease, so an X-ray supports a suspicion rather than proving one. It is still worth taking, because it rules out the other 3 candidates in a single visit and gives a baseline for the recheck at 4 to 8 weeks.
Treatment, and the recheck that proves it worked
The usual course is a dewormer given 3 times at 14-day intervals, timed to catch larvae as they mature; some cats need a second round. A short course of anti-inflammatory support is sometimes added when the airway is very reactive. The cough can take 3 to 6 weeks to settle even after the worms are gone, so a quiet chest at 2 weeks proves little. Repeat the Baermann test 4 weeks after the last dose, and again at 3 months if the cat hunts. Cats in a multi-cat household should all be tested, because shared litter trays and shared hunting grounds spread the infection.
Prevention for cats that go outside
Monthly deworming through the warm months, from 1 dose in spring to 1 every 4 weeks until the first frost, covers the period when slugs are active. Remove snails from potted plants, wash outdoor water bowls daily, and stop the cat from eating raw prey it brings in. Indoor cats are low risk but not zero risk: a single slug in a plant saucer is enough, and the cat that never leaves the flat can still test positive at 4 years old.
Cost, and when to stop waiting
A Baermann test runs 40 to 90 USD, PCR 90 to 180 USD, chest films 150 to 300 USD, and an airway wash 400 to 800 USD; a course of treatment lands near 30 to 90 USD. Typical figures are collected in the cat cost guide. Stop waiting and book the visit if the cough has lasted 3 weeks, if breathing at rest is over 40 a minute, if the gums look pale or blue, or if the cat stops eating for 24 hours.
Two conditions overlap enough to be worth reading about: pain scoring helps you judge whether the cat is uncomfortable rather than merely quiet, and the vaccine schedule is the right moment to ask about parasite cover, since lungworm is not covered by the core vaccines.
Frequently asked
Can an indoor cat get lungworm?
Yes. Larvae travel in the slime of slugs and snails, so a cat can be infected by contact with a plant saucer, a doorstep, or a toy left outside. Indoor cats are lower risk than hunters, but a single slug in a potted plant is enough, and infections in cats that never go out are diagnosed often enough to keep the test on the list.
How is lungworm different from asthma?
The cough, the wheeze and the X-ray pattern can look identical, and both respond to anti-inflammatory treatment at first. The differences are age at onset, outdoor access, weight loss with a normal appetite, and the fecal test. Asthma is managed for life with inhaled drugs; lungworm is cleared with 3 deworming doses at 14-day intervals and confirmed by a repeat test 4 weeks later.
Is one negative fecal test enough to rule it out?
No. Larvae are shed in waves, and a single Baermann sample misses roughly 1 in 3 infected cats. If the cough has lasted 3 weeks, ask for 3 samples across 3 days or a PCR test, and treat a strong clinical picture rather than relying on one clean result.