Lungworm in Dogs: The UK Epidemic & Why Your Vet Mentions It

By Sarah Bennett, Certified Animal Nutritionist

If you live in the UK and your vet has mentioned lungworm recently, it is not alarmism or a sales pitch. Angiostrongylus vasorum — known colloquially as the French heartworm — is an emerging and genuinely dangerous parasite that has undergone a dramatic range expansion across the British Isles over the past two decades. What was once a curiosity seen mainly in fox populations in southern England is now a confirmed threat to dogs in every part of the UK. Every dog owner needs to know what it is, how it spreads, and why prevention cannot wait.

What Is Angiostrongylus vasorum?

Angiostrongylus vasorum is a nematode worm — not the same as common intestinal roundworms. Rather than living in the gut, adult lungworms migrate to and live in the pulmonary artery (the major blood vessel carrying blood from the heart to the lungs) and the right side of the heart. This placement — inside the vascular system — is what makes the parasite so dangerous. Larvae are released into the bloodstream, travel to the lungs, hatch, and are coughed up or swallowed and passed in faeces.

The parasite's name is slightly misleading: while often called "lungworm," the adult worms primarily inhabit the pulmonary arteries and heart, not the lung tissue itself. The pathology they cause — vascular inflammation, pulmonary hypertension, and coagulopathy — is cardiovascular in nature.

How Dogs Become Infected

The life cycle of Angiostrongylus vasorum requires an intermediate host: slugs and snails. Larvae passed in dog or fox faeces are ingested by slugs and snails, where they develop into the infectious stage. When a dog eats an infected slug or snail — or even the slime trail left behind — it can become infected.

This is the key fact that changes how we think about risk. Dogs do not need to deliberately seek out and eat slugs. Accidental ingestion is common: a dog sniffing through undergrowth, eating grass, drinking from outdoor water bowls that slugs have crossed, or playing with toys left outside overnight can all inadvertently consume infected material. Puppies and curious young dogs that put everything in their mouths are at particularly high risk, but so is any dog with outdoor access.

Foxes are a significant wildlife reservoir for the parasite, and the expansion of urban fox populations across the UK has been closely linked to the spread of lungworm into regions where it was previously unknown.

Symptoms That Are Easily Missed

Lungworm is genuinely difficult to diagnose on symptoms alone, because its clinical presentation is so variable. Common presentations include:

Respiratory signs: Persistent coughing, wheezing, and exercise intolerance due to pulmonary inflammation and hypertension. These are often mistaken for kennel cough, bronchitis, or asthma.

Coagulopathy (bleeding disorders): One of the most distinctive — and alarming — features of lungworm infection is disruption of normal blood clotting. Infected dogs may present with unusual bleeding from minor wounds, bleeding from the nose or gums, bruising easily, or blood appearing in urine or faeces. Some dogs bleed into the eye. This coagulopathy is caused by the parasite interfering with platelet function and clotting cascade proteins.

Neurological signs: In severe cases, larvae migrating to unusual sites or the effects of the coagulopathy can cause seizures, spinal cord haemorrhage, and sudden paralysis. Dogs have died within days of presenting with these signs.

General illness: Weight loss, lethargy, poor appetite, and vomiting are all reported but are non-specific and easily attributed to other causes.

The insidious nature of early-stage infection — when the parasite is present but symptoms are mild or absent — means dogs are often not diagnosed until significant damage has occurred.

Diagnosis and Treatment

Diagnosis is confirmed by the Baermann technique or modified Baermann faecal examination to detect larvae in stool, or by the ANGIO Detect rapid antigen test, which detects lungworm antigens in blood — a quick in-clinic test now offered by many UK veterinary practices. Chest X-rays and blood tests showing clotting abnormalities support the diagnosis.

Treatment with licensed anti-parasitic drugs — particularly imidacloprid combined with moxidectin (the Advocate spot-on) — is effective when the infection is caught early. Severely affected dogs may require additional supportive care including blood transfusions, plasma, and hospitalisation. Treatment is most successful before extensive vascular or clotting damage has occurred — another reason early diagnosis and prevention matter so much.

Monthly Prevention: The Only Reliable Protection

Advocate (imidacloprid + moxidectin) applied monthly as a spot-on is currently the only licensed product in the UK with a claim for preventing lungworm infection. It kills larvae before they can establish as adults and is also effective against fleas, roundworms, heartworm, and mange mites — making it an excellent all-in-one parasiticide for UK dogs. Other common spot-on products (Frontline, Stronghold) and standard worming tablets do not cover lungworm.

Additional precautions include removing slugs and snails from the garden where possible, not leaving dog toys or food bowls outside overnight, and discouraging dogs from eating grass or drinking from puddles in high-risk areas.

References

1. Morgan ER, Jefferies R, van Otterdijk L, et al. "Angiostrongylus vasorum infection in dogs: presentation and risk factors." Vet Parasitol. 2010;173(3-4):255-261. PMID: 20728996
2. Chapman PS, Boag AK, Guitian J, Boswood A. "Angiostrongylus vasorum infection in 23 dogs (1999–2002)." J Small Anim Pract. 2004;45(9):435-440. PMID: 15473303

Written by Sarah Bennett, Certified Animal Nutritionist. This article is for informational purposes only and does not substitute professional veterinary advice.