CONDITION

Angiostrongylus (Lungworm)

Why this matters now

Angiostrongylus vasorum, commonly called French heartworm or lungworm, has become increasingly prevalent across the UK over the past two decades. Dogs acquire infection by ingesting slugs, snails, or their slime trails—often accidentally whilst eating grass, drinking from puddles, or playing with toys left outdoors. Younger dogs appear more commonly affected, possibly due to exploratory behaviour. The parasite poses a genuine health risk and warrants awareness amongst dog owners.

After ingestion, larvae migrate through the body, eventually reaching the heart and pulmonary arteries where adult worms develop. Larvae shed by adults travel to the lungs, causing inflammation. The lifecycle takes approximately seven weeks from infection to adult worms producing new larvae. Clinical signs can range from mild coughing to life-threatening bleeding disorders, depending on worm burden and individual response.

Signals & patterns

Early signals

Coughing

A persistent cough develops as larvae migrate through lung tissue and cause inflammation.

Reduced exercise tolerance

Dogs tire more easily during walks or play.

Weight loss

Gradual weight loss may occur despite maintained appetite.

Breathing changes

Faster or more laboured breathing, particularly after exertion.

Later signals

Unexplained bleeding

Bruising, prolonged bleeding from minor wounds, or bleeding from gums without obvious cause.

Pale gums

Anaemia from chronic infection or blood loss causes visible pallor.

Collapse or weakness

Severe cases may cause sudden collapse due to bleeding or heart effects.

Neurological signs

Bleeding into the brain or spinal cord can cause seizures, blindness, or incoordination.

Click to read about the biological mechanisms

How this is usually investigated

Diagnosis involves specific tests to detect the parasite, along with assessment of any complications. Early detection before severe signs develop improves outcomes.

Faecal Baermann test

Purpose: To detect larvae shed in faeces
Considerations: This specialised faecal test concentrates larvae for microscopic identification. It may be negative if sampling occurs before larvae are shed or in low-burden infections.

Antigen blood test

Purpose: To detect circulating parasite proteins
Considerations: Rapid in-clinic tests and laboratory tests are available. Detects adult worms. Highly useful for diagnosis and monitoring treatment response.

Clotting tests

Purpose: To assess for bleeding disorders
Considerations: Prolonged clotting times indicate coagulopathy requiring urgent attention.

Chest radiographs

Purpose: To evaluate lung changes and heart size
Considerations: May show characteristic lung patterns, enlarged pulmonary arteries, or heart changes. Helps assess disease severity.

Complete blood count

Purpose: To check for anaemia and blood cell changes
Considerations: Low red blood cells indicate blood loss. Elevated eosinophils are common with parasitic infection.

Options & trade-offs

Treatment involves antiparasitic medication to kill the worms. Supportive care addresses complications. Prevention through regular prophylaxis is highly effective.

Antiparasitic treatment

Specific licensed products that kill Angiostrongylus worms.

Trade-offs: Several licensed products are effective. Worm death can temporarily worsen inflammation before improvement. Multiple treatments may be needed.

Treatment of coagulopathy

Fresh frozen plasma, vitamin K, or blood transfusion for dogs with bleeding disorders.

Trade-offs: May be lifesaving in severe cases. Addresses the dangerous complication whilst anthelmintics work.

Anti-inflammatory medication

Corticosteroids to reduce lung inflammation caused by dying parasites.

Trade-offs: Often used alongside antiparasitic treatment. Reduces inflammatory response that contributes to signs.

Supportive care

Oxygen therapy, rest, and monitoring for dogs with respiratory compromise.

Trade-offs: Severity determines level of support required. Most dogs respond well to appropriate treatment.

Monthly prevention

Regular prophylactic treatment to prevent establishment of infection.

Trade-offs: Highly effective at preventing disease. Various products are available. Particularly valuable in endemic areas.

Common misconceptions

Misconception:

"My dog does not eat slugs, so cannot get lungworm"

Reality:

Dogs often ingest slugs, snails, or slime trails accidentally—through grass eating, drinking from outdoor water bowls, or playing with garden toys. Intentional consumption is not required.

Misconception:

"Lungworm is rare in the UK"

Reality:

Angiostrongylus has spread throughout the UK and is now endemic in many areas. Risk varies by region but is present in most parts of the country.

Misconception:

"Standard wormers prevent lungworm"

Reality:

Not all wormers are effective against Angiostrongylus. Specific products licensed for lungworm prevention are required. Regular broad-spectrum wormers may not provide protection.

Understanding local lungworm prevalence helps inform prevention decisions. Noting any coughing, changes in exercise tolerance, or unexplained bleeding prompts earlier investigation. Being aware that prevention requires specific products, not all wormers, helps ensure appropriate protection. Reducing garden slug and snail populations and bringing outdoor water bowls inside may lower exposure risk.

Last reviewed: 24 April 2026 · Dr Alastair Greenway MRCVS