Feline Lungworm

Feline lungworm disease is caused most often by Aelurostrongylus abstrusus, a small parasitic nematode that completes its adult life in the tiny airways and air sacs of a cat's lungs. It is an easily overlooked cause of coughing in cats because its signs mimic more familiar conditions such as feline asthma or a lingering respiratory infection.

The parasite has an indirect life cycle. Adult worms in the lungs lay eggs that hatch into larvae; the cat coughs these up, swallows them, and passes them in the faeces. The larvae must then be eaten by a slug or snail to develop further. Cats rarely eat molluscs directly, so infection usually happens when a cat hunts and eats a bird, rodent, frog or reptile that has itself swallowed an infected slug or snail.

Once inside a new cat, the larvae travel through the body to the lungs, mature over about five to six weeks, and begin the cycle again. Light infections may cause few signs, but heavier worm burdens trigger a persistent cough, wheezing and increased breathing effort as the airways become inflamed. Kittens, older cats and those with other illnesses tend to be worst affected.

Diagnosis relies on finding the distinctive larvae in a fresh faecal sample — often using a special technique called the Baermann test — or on examining fluid washed from the airways. Because larvae are shed intermittently, several samples over consecutive days may be needed. Chest X-rays typically show a patchy, blotchy pattern in the lungs.

The outlook is good. Modern anti-parasitic treatments clear the infection reliably, and most cats' airways settle over the following weeks. The best long-term protection is a parasite-control routine suited to a hunting cat, discussed with your vet, along with anything that reduces how much wildlife your cat catches and eats.