Lungworm in Dogs and Cats: Signs, Treatment, and Prevention

What lungworm is

Several different worms are called lungworms. In dogs, the one that causes the most concern is Angiostrongylus vasorum, often called the French heartworm. The adult worms live in the right side of the heart and the large blood vessels of the lungs. Their larvae damage lung tissue, and the infection can upset normal blood clotting. Dogs can also carry the fox lungworm, Crenosoma vulpis. It lives in the windpipe and airways and usually causes a less serious illness.

In cats, the most common species is Aelurostrongylus abstrusus, known as the cat lungworm. A related worm called Troglostrongylus is found less often. It has been reported mainly in southern Europe, including Italy, Spain, Greece, and Portugal, and it can cause severe disease in kittens. Other worms can reach the lungs too. Roundworm larvae pass through the lungs of young puppies on their way to the gut, and heavy burdens occasionally cause pneumonia. A small airway worm, Eucoleus aerophilus, can infect dogs, cats, and foxes.

Where lungworm is found

European parasite experts describe the French heartworm as present across Europe in local hot spots. In many places it is now reported over wider areas than before, in both dogs and wild animals. Red foxes are an important wild source of infection. Wolves and golden jackals can carry it too.

In the Balkans, studies have found the French heartworm in red foxes in northern and central Serbia, and in foxes and golden jackals in northern Bosnia and Herzegovina. The researchers in Bosnia suggest that spreading jackal populations may help the parasite move through Southeastern Europe. A countrywide survey of dogs in Greece found evidence that the parasite circulates in local dogs. The cat lungworm occurs throughout Europe, and studies in some countries have found it in up to 30 percent of the cats tested.

How pets catch it

The life cycle runs through slugs and snails. An infected animal coughs up larvae, swallows them, and passes them in its feces. Slugs and snails pick up these larvae, which develop inside them until they can infect a pet. Dogs are usually infected by eating slugs or snails, on purpose or by accident. Larvae can also leave slugs and snails and end up on grass or in puddles, so a dog can pick them up by chewing grass or drinking outdoor water. In experiments, these larvae stayed infective for at least eight weeks. Frogs can also carry the larvae.

Cats are most often infected by eating prey that has eaten infected slugs or snails, such as mice, birds, lizards, and frogs. They can also swallow the larvae directly from slugs and snails. After infection, it takes several weeks, and sometimes longer, before larvae start to appear in the feces.

The main lungworms do not spread directly from one pet to another through play or coughing, because the larvae must first develop inside a slug or snail. Pets that share a yard can still be exposed to the same slugs and snails, so if one pet is diagnosed, ask your vet whether the others should be checked. The French heartworm and the fox lungworm infect dogs but not cats, and the cat lungworm is specific to cats. These worms are not considered a health risk for people. The airway worm Eucoleus aerophilus has caused very rare human infections, so washing your hands after handling feces is a good habit.

Signs to watch for

Signs can take weeks or months to appear, and some pets never show any. Dogs with the French heartworm most often cough, breathe faster, tire quickly on walks, lose weight, or eat less. Some develop bleeding problems, such as nosebleeds, small cuts that keep bleeding, bruises, or soft swellings under the skin. Others cough up blood or pass black, tarry stools. In rare cases the larvae or bleeding affect the brain or eyes, which can cause wobbliness, weakness, seizures, or changes in vision.

The fox lungworm usually causes a long-lasting cough, sometimes with sneezing or faster breathing. It is easily mistaken for an allergic airway problem.

Cats with lungworm may cough, sneeze, breathe faster, breathe with their mouth open, or have a runny nose. Some lose weight, eat less, or seem tired. Many infected cats show no signs at all. In severe cases the airways and lungs become inflamed, and without treatment the infection can be fatal. Signs in cats can look like feline asthma, so your vet may test for lungworm before settling on another diagnosis.

When it is an emergency

Contact your vet or an emergency clinic right away if your pet shows any of these signs.

• Struggling to breathe, or breathing with the mouth open (in cats this is an emergency)
• Blue, gray, or very pale gums
• Coughing up blood, or bleeding that will not stop
• Sudden weakness, collapse, or a seizure

Dogs with the French heartworm can bleed inside the body, and in rare cases the infection causes sudden death. A dog with unexplained bruising or bleeding should be seen by a vet the same day.

How vets test for it

Your vet will usually start with an exam and questions about coughing, bleeding, hunting, and whether your pet eats slugs, snails, or grass. It helps to say where your pet has lived and traveled. A routine stool test for worm eggs can miss lungworm, so vets often use a special stool test called a Baermann test to look for live larvae. Larvae are shed on and off, so your vet may ask for fresh samples from three separate bowel movements, collected over one to three days and kept apart.

For dogs, a blood test for the French heartworm is also available. Chest X-rays or a CT scan show how much the lungs are affected, though the changes can look like other lung diseases. Dogs with bleeding signs usually have blood clotting tests. In some cases, the vet washes a small sample out of the airways under anesthesia and checks it for larvae.

How it is treated

Lungworm is treated with antiparasitic medicine. Depending on the worm and the product, this may be a single treatment, a treatment repeated over several weeks, or a daily course. Pets that are very sick may need hospital care, such as oxygen, fluids or a blood transfusion, medicine to calm inflammation, antibiotics for a secondary infection, and treatment to control bleeding. Rest is usually advised during treatment. Your vet may suggest a follow-up test after treatment to check that it worked. Many pets recover well, especially when lungworm is found early.

Lowering the risk

Not every dewormer covers lungworm. European parasite guidelines suggest that dogs at higher risk, such as those that eat slugs, snails, or grass in areas where the French heartworm is found, may need monthly prevention or regular testing. For cats that go outdoors and hunt in areas where the cat lungworm is common, the same guidelines suggest monthly prevention all year. Your vet can advise which product fits your pet and your area, and how often to give it. A few everyday habits also help.

• Pick up your dog's feces promptly, on walks and in the yard.
• Bring toys and food and water bowls inside at night so slugs and snails cannot crawl into them.
• Discourage your dog from eating grass, slugs, or snails and from drinking out of puddles.
• Remove slugs and snails from the yard, and use only garden products that are safe for pets.
• Limit your cat's hunting where you can, especially in areas where the cat lungworm is common.

Rescued and newly adopted pets

Street dogs and cats often scavenge for food or hunt, and these habits bring them into contact with slugs, snails, and infected prey. Stray and feral cats are at higher risk than pet cats. Because signs can appear weeks after infection, a pet can seem healthy on arrival and develop a cough later.

At Paw Squadron, the first stops after every rescue are the vet and a bath, with a checkup, deworming, and treatment against fleas and other parasites. Every animal also gets a checkup, treatment, vaccinations, and a microchip before adoption. Dewormers differ in which worms they cover, so it is a good idea to take your new pet's records to your own vet, mention where the animal came from, and ask whether a lungworm test or a lungworm preventive makes sense where you live. If your new dog or cat starts to cough, breathes fast, or shows unusual bleeding, book a vet visit. You can find more guides on parasites and pet health in PawPedia.