You should seek the advice of your veterinarian if your pet is ill as only he or she can correctly advise on the diagnosis and recommend the treatment that is most appropriate for your pet.

Lungworms are an uncommon cause of coughing in cats

Lungworms are common in most countries of the world, and Aerulostrongylus abstrusus and others (including Capillaria aerophilia, Filaroides hirthi, Osleroides massinoi, Trogostrongylus subcrenatus and Trogostrongylus brevior) may infect the respiratory tract of cats. In some countries up to 20% of cats living in rural areas may be infected.

The natural life-cycle of many of these worms involves other "intermediate" hosts such as slugs and snails and cats become infected by eating them, or by eating another animal (eg a bird or rodent) that has eaten an infected host. Once inside a cat the larval form of  Aerulostrongylus  travels to the lungs via the bloodstream. In the lungs the adult worms develop to become thin hair-like worms up to 10mm in length. The adults then lay eggs which hatch into first-stage larvae and are coughed up by the cat and swallowed to be passed out in the faeces. Once in the environment these larvae are then eaten by snails or slugs and the cycle begins again.

Lungworm infections most often affect outdoor cats which are hunters.

Many cats infected with lungworms show no clinical signs at all whereas others may have a longstanding cough or wheezing, and cats infected with Capillaria hoehmi may develop a nasal discharge and sneezing. Studies have shown that as few as 50 Aerulostrongylus larvae can cause lung tissue damage, but as many as 800 larvae are needed before a cat will show signs of difficulty breathing or coughing. The cat eventually eliminates the adult worms after 3-4 months. The worm Filaroides hirthi has a life-cycle that does not involve any intermediate hosts, and infection with this parasite causes more severe respiratory signs and pneumonia, especially in animals with poor immunity.

Diagnosis of lungworm can be difficult because changes on XRays of the chest may not be helpful. Recognising larvae in faeces samples using a specific test (the Baermann technique)  is the usual way in which the condition is diagnosed, but false negative tests are common and repeat samples often have to be taken because the larvae are not shed into the faeces all the time.

Lungworms in cats can be treated using a variety of worming products (eg ivermectin, benzimidazoles). Control of snail and slug (mollusc) populations in gardens may also be worthwhile.

In some parts of the world (North America, Far East, Africa and Latin America) cats can be infected with another parasite -  Paragonimus spp - which is a type of fluke. This also has larval stages and intermediate hosts (aquatic snails, crayfish, crabs) and it  lives in cystic cavities in the lungs of infected cats causing mild signs usually, but occasionally severe signs such as coughing up blood and collapse of the lung if a cyst ruptures (a condition called pneumothorax).This disease can be treated using fenbendazole or praziquantel.

Fortunately the lungworms of cats are not transmitted to humans.

Updated October 2013