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Lungworm/French Heartworm (Angiostrongylus vasorum) in dogs

What is lungworm?

Lungworm larvae are found in infected slugs, snails and frogs.  Lungworm can be found all over the U.K. but more commonly in southern England and Wales. Dogs and foxes can become infected with the parasite by eating infected slugs or snails, or coming into contact with the areas they have passed over (slime trail).

What are the symptoms of Lungworm?

The symptoms of lungworm can often be confused with other illnesses with mild cases often going unnoticed. The symptoms to look out for are: –

  • Lack of appetite
  • Weight loss
  • Breathing difficulties
  • Coughing (possibly bringing up blood)
  • Lethargy
  • Vomiting
  • Diarrhoea
  • Increased bleeding (a cut or graze will bleed for longer than usual)
  • Haemorrhages

How is lungworm transmitted?

Slugs and snails can carry the lungworm parasite where it is transmitted by a dog or fox ingesting the infected slug or snail. Once ingested, the lungworm larvae migrate through the intestinal walls to the heart where the adult worms live within the pulmonary artery and right ventricle of the heart.  The eggs hatch in the lungs and the young microscopic larvae are coughed up or pass out in faeces where they are then ingested by slugs and snails, completing the life cycle.

Lungworm cannot be passed from dog to dog as the lungworm needs to be ingested by a slug or snail, where it can grow and develop.

What are the risk factors?

Dogs that are prone to rummage through undergrowth and eat grass, or even chose to eat slugs and snails, are most at risk.  Small slugs can become attached to an animal’s fur and unintentionally eaten while grooming.  Even contact with the slime trail left by snails and slugs on outside food and water bowls can pose a risk of infection.

Lungworm infection can be progressive and often symptoms do not become apparent for months. If your dog is showing signs of illness, take him to see your vet as soon as possible as, if left untreated, the lungworm parasite can cause damage to the heart and lungs which can ultimately be fatal.


You will be asked about your pet’s history, habits and symptoms.  The vet will undertake a thorough examination and test for the presence of the lungworm parasite by taking blood and stool samples. Once diagnosed, your dog will be given a course of treatment.  Even if your vet cannot find signs of the lungworm itself, they may choose to treat your dog for lungworm as a precautionary measure, especially if his symptoms indicate infection.

If caught early, no further treatment will be necessary and your pet should make a full recovery.

What treatment is treatment is there for lungworm?

When the disease is caught early, a routine anti-parasite treatment is all that will be needed to clear your dog of the infection.

How can lungworm be prevented?

Ask your vet about preventative treatments that will protect your dog against lungworm.  When out walking or in the garden be vigilant if you see any slugs or snails and always pick up and safely dispose of your dog’s poop. Remove toys and food bowls from the garden to avoid slugs and snails coming into contact with them. If your dog is showing any symptoms, take him to the vet to get him checked over.