Lungworm in Dogs: Signs, Risks and Prevention

At a glance

What it is	A parasitic worm that lives in the heart and the large blood vessels supplying the lungs
Who's at risk	Any dog, especially young dogs and those who eat grass, play with toys outdoors or drink from puddles
Main signs	Coughing, breathing difficulties, tiredness, bleeding or bruising, weight loss and sometimes changes in behaviour
Contagious?	Not directly from dog to dog; dogs catch it from infected slugs, snails and frogs
Can it be prevented?	Yes, the risk can be greatly reduced with regular prevention prescribed by your vet

What it is

Lungworm is a type of parasitic worm. Despite the name, the adult worms in dogs actually live in the heart and in the major blood vessels that carry blood to the lungs. The worm most often meant by "lungworm" in dogs is called Angiostrongylus vasorum, and it has been reported in more areas over recent years.

The life cycle involves slugs and snails. Here is how it works in simple terms:

1. Adult worms in an infected dog lay eggs, which hatch into larvae in the lungs.
2. The larvae are coughed up, swallowed and passed out in the dog's faeces.
3. Slugs and snails become infected when they eat or come into contact with these faeces.
4. A dog then becomes infected by eating an infected slug or snail, or by swallowing the larvae from the slime trail they leave behind.
5. The larvae travel through the dog's body to the heart and lung blood vessels, where they grow into adults and the cycle begins again.

Frogs can also carry the larvae, and foxes can become infected too, which helps the parasite spread in the wider environment.

How dogs pick it up

Some dogs deliberately eat slugs and snails, but many become infected by accident. Tiny slugs can cling to:

• Toys and balls left outside overnight
• Water and food bowls kept in the garden
• Puddles and outdoor water containers
• Grass, which some dogs like to chew
• Sticks and other things dogs carry in their mouths

Because slugs and snails are most active in mild, damp weather, the risk is often higher in spring and autumn, though infection can happen at any time of year.

Signs to watch for

Lungworm can cause a wide range of signs, and they vary a lot from dog to dog. Some infected dogs seem completely well for a long time, while others become seriously unwell.

Signs may include:

• Breathing problems. Coughing, breathing faster or harder than usual, or getting out of breath easily.
• Tiredness. Reduced energy, tiring quickly on walks or seeming less keen to play.
• Bleeding problems. Lungworm can interfere with the blood's ability to clot. You might notice nosebleeds, bleeding from the gums, bleeding that takes a long time to stop after a small cut, bruising, or small red spots on the gums or skin. Bleeding can also happen inside the body where you cannot see it.
• General illness. Weight loss, poor appetite, vomiting or diarrhoea.
• Behaviour changes. In some cases, bleeding near the brain or spine can cause changes in behaviour, wobbliness, weakness or seizures.

Many of these signs are not specific to lungworm and can be caused by many other conditions. If your dog has developed a cough, our guide to dog coughing and our symptom checker can help you think through what to do next.

When to see a vet

Book an appointment with your vet if your dog has a cough that does not settle, seems more tired than usual, is losing weight or just does not seem themselves, especially if they are known to eat slugs, snails or grass.

Contact your vet urgently if your dog:

• Is struggling to breathe or breathing very fast at rest
• Has unexplained bleeding or bruising, or bleeding that will not stop
• Collapses, has a seizure or suddenly becomes wobbly or weak
• Has pale gums

If you know your dog has eaten a slug or snail and they are not on regular lungworm prevention, it is worth calling your vet for advice, even if your dog seems well.

How vets diagnose it

Your vet will start by examining your dog, listening to their chest and asking about their lifestyle, including whether they eat slugs, snails or grass, and what parasite prevention they are on.

There are several ways vets can test for lungworm:

• Blood tests. A quick test can detect signs of the parasite in a blood sample, often while you wait or within a short time. Other blood tests can check how well the blood is clotting.
• Faecal tests. Samples of your dog's faeces, often collected over several days, can be examined for larvae. Because larvae are not passed every day, more than one sample is usually needed.
• Imaging. Chest X-rays or other scans may show changes in the lungs and help rule out other causes of coughing or breathing problems.
• Other tests. In some cases, a sample of fluid from the airways may be taken.

A single negative test does not always rule lungworm out completely, so your vet may recommend repeating tests or combining different types.

Treatment and management

Lungworm is treatable, and many dogs make a full recovery, especially when it is caught early. Treatment is prescribed by your vet and usually involves medication to kill the parasites.

Dogs with more severe illness may need extra care, which can include:

• Hospital stays for monitoring
• Oxygen support if they are struggling to breathe
• Treatment to help with bleeding or clotting problems
• Medication to manage inflammation in the lungs
• Strict rest

While your dog is recovering, your vet may advise restricting exercise. As the worms die, they can cause inflammation in the lungs and blood vessels, and keeping your dog calm reduces strain on the heart and lungs during this time.

Your vet will usually want to see your dog again after treatment, and may repeat tests to check the infection has cleared. Finishing every part of the treatment plan and going to these follow-up appointments is important.

Prevention

The good news is that the risk of lungworm can be greatly reduced. The most reliable approach combines vet-prescribed prevention with a few simple habits at home.

Regular prevention from your vet

Not all worming products protect against lungworm, so it is worth checking. Your vet can recommend a prevention product that covers lungworm and explain how often it needs to be given. These products work best when given regularly and on time, all year round, rather than only when you remember. Setting a reminder on your phone or calendar can help.

Habits that lower the risk

• Bring toys and bowls inside at night. Slugs and snails are most active after dark and may crawl over anything left outside.
• Empty and refresh outdoor water regularly. Avoid leaving water bowls or containers standing in the garden.
• Discourage slug and snail eating. Some dogs find them interesting, so supervise young or curious dogs and gently redirect them.
• Pick up after your dog promptly. This helps stop the parasite's life cycle continuing in your area.
• Discourage drinking from puddles where you can, and offer fresh water on walks instead.
• Think carefully about slug pellets. Many are toxic to pets. If you need to control slugs in the garden, ask about pet-safe options. Our toxic foods and substances guide has more on hazards around the home.

Living with it

Most dogs treated for lungworm recover well, and many go on to live completely normal lives. A few dogs who were very unwell may have some lasting changes to their lungs or heart, and your vet will talk you through any ongoing care these dogs need.

Once your dog has recovered, the key is to keep up with regular prevention, as having lungworm once does not protect a dog from catching it again. If you move to a new area, it is worth asking your vet whether lungworm is common locally, so you can make an informed decision about prevention together.