Lungworm in Cats

Lungworm is a generic term for a parasite that infects the lungs. I’ve thankfully never diagnosed a case of cat lungworms during my veterinary career so far. While it can go undetected and not cause symptoms, feline lungworm can be serious in young cats, so it’s worth knowing what to look for — especially if you have an active, outdoor cat who enjoys hunting. 

Let’s look closely at lungworm in cats, how they get it, and how to protect your cat.

What Is Lungworm in Cats?

Cats can get several different lungworms in North America. The most common type in domestic cats is Aelurostrongylus abstrusus, but cats can also get several other species of lungworm. 

Cats with lungworm have adult worms living inside their lungs, and immature larvae moving around the lungs. The irritation causes coughing, and the worms can take up so much space that cats have problems breathing. It can be distressing for cats, and the symptoms can become severe enough to become fatal — especially in young kittens, who can get the infection from their mother’s milk. 

How Do Cats Get Lungworm?

Cats usually catch the lungworm by eating infected rodents or birds (for most species — although one parasite species can also be picked up from cat poop). Once they’ve been eaten, the parasite enters the bloodstream and travels to the lungs, where they mature into adults. These adult parasites produce eggs, which hatch, and the first-stage larvae are coughed up and swallowed. 

These tiny larvae survive the stomach and intestines and are then passed in the poop, ready to infect a slug or snail. Inside the slug or snail they mature, and are then able to infect cats again — although usually, they first infect a mouse or bird that eats the slug or snail.  

This means outdoor cats, and especially strays who hunt a lot, are much more likely to have cat lungworm than those who spend most of their time indoors.

Most lungworms need to spend some time in an intermediate host (in this case, the snails/slugs) to develop properly. This means cats can’t normally catch lungworm from one another. But one type of lungworm is infectious as soon as it’s passed in feces and can be caught by in-contact cats and other animals, including humans, causing bronchitis with a productive cough.

Signs of Lungworm in Cats

The signs of lungworm in cats vary hugely. In some cases, cats can be infected with lungworms without showing any signs at all. This is called an asymptomatic infection. This is more likely at an early stage of the disease. As the adult worms grow and take up more space and produce more eggs and larvae, there’s more damage to the lungs and more symptoms. Asymptomatic infections are also more likely if cats are infected with only a small number of worms. The more larvae they ingest, the worse their symptoms are likely to be.

A cat with lungworm might have:

• A cough (usually a productive one, followed by a swallow)
• Nasal discharge
• Fever
• Fast breathing
• Lymph node enlargement
• Lethargy
• Weight loss
• Difficulty breathing
• Blue-tinged gums 

In some cases, lungworm infections are undiagnosed until animals die under anesthetic, and the infection is found on post-mortem. One important thing to note is that you don’t expect to see worms in cat poop if they’ve got lungworm. Although the lungworm parasite does come out in the poop, it’s the very tiny first-stage larvae and not the adult worms. They can’t be seen without a microscope, so worms in a cat’s poop are not a sign of lungworm (although mixed infection with several types of worms is possible, too).

Diagnosing Lungworm in Cats

Vets usually suspect lungworm based on a cat’s history and age. A young cat who spends lots of time outdoors is more likely to have feline lungworm than an indoor-only cat or one who is much older.

Once the adult worms are old enough to start producing eggs (about 4-6 weeks after the infective larvae were ingested), then vets can usually find first-stage larvae in the poop. A smear of poop is examined under the microscope to look for the first-stage larvae, which are very active and easy to see (although difficult to distinguish from some other larvae). Eggs aren’t produced consistently, so collecting poop over several days or trying again several times might help.

There are several other tests that might help identify lungworm in cats. The best is probably a PCR test, which checks the poop (or a throat swab) for the presence of lungworm DNA. This is low-risk and not very invasive, with a high chance of success. Worms might also be seen on a lung wash or Bronchioalveolar Lavage – BAL, which is where sterile water is pushed into an anesthetized cat and then sucked out, and the liquid is sent for testing. The problem with this technique is that it’s invasive and risky, especially to a cat who already has symptoms of lung trouble. 

While lungworm in cats can’t be diagnosed on X-ray alone, it’s likely your vet will take X-rays as part of a workup for coughing in cats as it can help rule out other diseases. Unfortunately, the signs of cat lungworm on X-ray are non-specific. The thickened airways and pneumonia can look like asthma, which causes similar symptoms. Similarly, while they won’t usually see any worms, using a video camera (bronchoscope) can be helpful to rule out other diseases and visually see the damage to the lungs to help guide treatment.

Lungworm in Cats Treatment

Treating the actual feline lungworm itself isn’t particularly difficult. Many anti-parasite products on the market have been proven to cure the lungworm. The main problem comes with treating the inflammation, secondary infections, and any complications caused by the worms themselves. In cats with moderate to severe symptoms, antibiotics and anti-inflammatory steroids may need to be given as well, and they may need to be hospitalized for oxygen therapy while the treatment begins. There are no home remedies to cure lungworms in cats. 

Once your cat has had their anti-parasite medication, you’ll need to watch them closely. It’s possible for the death of the parasites to cause cats to feel worse for a short time, so keep an eye on their breathing and energy levels and call your vet if you have any concerns.

Lungworm Medicine for Cats

Many common anti-parasite medications can treat lungworms in cats, although their use against lungworms may be considered “off-label.” The following are most commonly used:

• Imidacloprid + moxidectin (Advantage Multi): a spot-on anti-parasite medication that kills adult worms
• Emodepside + praziquantel (Profender): a spot-on anti-parasite medication that kills adult worms 
• Fenbendazole (Panacur): An anti-parasite oral paste that kills the adult worms
• Prednisolone: An anti-inflammatory steroid

Cost of Treating Lungworm in Cats

Unfortunately, because lungworm is fairly rare, investigations to get a diagnosis can be expensive, especially as vets normally rule out more common causes of similar symptoms first. This means the cost of diagnosis can be high, ranging from $200-$1,000. Because lungworm in cats can usually be treated with normal anti-parasitic drugs, the actual cost of the drugs to treat lungworm can be quite low, as little as $50. The more severe the symptoms, the more it costs to treat, with cats needing hospitalization costing $300-$600 to treat.

How to Prevent Lungworm in Cats

Because most feline lungworms are spread through eating small prey, preventing cats from hunting will reduce the chance of them catching lungworm. Some cats find it very stressful to be kept indoors, but anti-hunting collars may help reduce their catch rate even if you’re letting them out.

For those prolific hunters or for stray cats, it’s possible to prevent feline lungworm with monthly medications from your vet. If this is the case, talk to your vet about your cat’s parasite prevention to make sure they’re covered.