Lungworms in cats

Aelurostrongylus abstrusus infection is relatively common in domestic cats and is the most important lungworm in cats (other lungworms are Troglostrongylus brevoir and Capillaria aerophila). Referring to Aelurostrongylus abstrusus as a lungworm is quite misleading. Although the early stages of the parasite do affect the lungs and severely infected cats may cough, other signs are far more common. The parasite itself may not cause the cat any problems unless present in very large numbers. All cats are potentially at risk but outdoor cats and particularly those with a compromised immune system are more at risk.

Bronchoalveolar lavage (BAL): wet preparation © Prof Richard Malik

The adult worm infects cats but the young stages are carried by slugs/snails, cockroaches, amphibians, rodents and birds. The adult worms spend most of their lives in the blood vessels close to the heart. However, when the eggs laid by the adults hatch, the immature worms (larvae) force their way through the walls of the blood vessels and into the lungs. The cat then coughs up the larvae and swallows them. The larvae pass into the feces which is in turn eaten by slugs and snails (which love cat poo!). Cats become infected by ingesting larvae when they eat slugs and snails, or other animals that have eaten the slugs and snails, eg rodents, frogs, lizards, snakes or birds. The larvae continue to develop in any new intermediate host until this is eaten by a cat. Transmission depends on cats ingesting intermediate or paratenic hosts. Once back in the cat the young worms make their way back through the cat's body to the blood vessels.

Most cats tolerate light infection with no clinical signs. Cats that are unwell show a wide range of symptoms: breathing problems, nasal discharge and coughing. Other animals may lose weight, have a reduced appetite, stop eating or become depressed. If your cat is unwell in any way make an appointment to see your veterinarian.

Your veterinarian may be suspicious of lungworm where there are compatible clinical signs and your cat is a known hunter. However, it is unlikely that your veterinarian will be able to confirm straight away what is wrong with your cat and they will need to do a number of tests (blood and fecal tests, X-rays, endoscopy and lung wash samples) in most cases to make the diagnosis. If you live in an area where lungworm is common your veterinarian may be more familiar with the disease and may be suspicious of the signs at an earlier stage. If there is a suspicion that your cat is infected your veterinarian can do a test for lungworms.

The infection can't pass direct from a cat without first passing through a slug or snail. However, if you have several pets living in the same household and one is found to be infected it is likely that the others will also be at high risk of infection. The common lungworm of cats (Aelurostrongylus abstrusus) does not affect dogs or people.

The aims of treatment are to eliminate the lungworm infection and also to manage the clinical signs. There are a number of drugs that can be used to eliminate the worms but infected cats should be monitored carefully when receiving treatment as the sudden killing of the worms can result in severe inflammation or an allergic reaction.

If your cat has severe signs your veterinarian will want to keep your pet in the hospital for specialized care.

Most affected cats go on to make a full recovery with appropriate treatment. However, infection can prove fatal for some cats despite intensive treatment.

Most cats are infected when hunting so if you can limit your cat's hunting that will reduce the risk.

Regular treatment of your cat with a product that can kill the worms can help to protect them against infection. The standard worming treatment that you give your pet every 3 months or so may not protect them from lungworm infections. You will need to get additional treatment from your veterinarian and this may be given in the form of a monthly spot-on (at the back of the neck) which will protect against lungworms and treats your cat for other common parasites such as fleas, worms, and mites. Contact your own veterinarian for further advice on the risks to your cat and how to manage them.