We’re all very much “lungworm aware” when it comes to dog lungworm (Angiostrongylus vasorum), but many people are unaware that cats have their own species of this parasite – Aelurostrongylus abstrusus. Unlike the dog version, this is often “clinically silent”, meaning that no symptoms are apparent. However, if the infestation is heavy enough, it can be very severe and even life-threatening.
What is the Cat Lungworm?
Aelurostrongylus abstrusus is a small nematode, or roundworm. Adults are about 7mm (⅓”, males) to 10mm (½”, females) long, and live inside the cat’s lung tissue. Here they lay eggs (starting about a month after the cat is infected), which are squeezed out into the airways and form nodules in the small airways. These then hatch into larvae which swim upwards until they irritate the tissue and are coughed out by the cat. They are then swallowed and passed in the faeces. Once in the outside world, these larvae infect slugs and snails, where they lay in wait. Every so often, an infected slug or snail is eaten by a rodent, or a bird, or a frog or similar, and the parasites move house to set up home in this animal (called a transport host). Sooner or later, the small animal will be eaten by a cat, and the worms are eaten with it. They then burrow out of the cat’s intestine into the tissues, and make their way through the body into the lungs (which takes about 24 hours). There they mature and begin the cycle again.
What cats are at risk?
Any cat who ever, even occasionally, catches wild prey. The prevalence is probably very high in outdoor and feral cats.
What are the symptoms?
Many cats will only have a fairly small infestation, and will never show any symptoms. In addition, in most cats the infection is fairly short-lived – after four to six months, the worms die and are destroyed. Cats with a moderate infestation may develop a cough, shortness of breath when exercising, wheezy breathing and weight loss – which symptoms may be subtle enough that an inexperienced or inattentive owner may not recognise them. However, in cats with a heavy infestation, symptoms typically include rapid breathing, severe distress, difficulty breathing, blue gums and collapse. In rare cases, it may even be fatal.
How is it diagnosed?
With a special test on the faeces of the infected cat called a Baermann Test (which looks for the larvae in the faeces). Sometimes, larvae, nodules or worms can be seen on endoscopy of the lungs.
Can it be treated?
Treatment of established cases requires advanced supportive treatment, with infected cats often needing oxygen therapy, intensive care and powerful anti-inflammatory drugs. In addition, long courses of drugs like fenbendazole (usually daily for two weeks) or doses of moxidectin/imidacloprid spot-on are used to kill the parasites.
Can it be prevented?
Regular worming with an ivermectin-based wormer will usually prevent infestations becoming severe enough to cause symptoms. However, hunting and outdoor cats should be wormed more frequently than the every three months recommended for indoor cats – usually every month or so, especially in active hunters.
If you cat seems to be having any trouble breathing, this is an emergency that needs advice from one of our vets as quickly as possible.