Two Lungworms, One Overlapping Symptom
When a dog presents with a persistent cough and a history of eating slugs or snails, two parasitic diagnoses should sit at the top of the differential list: Angiostrongylus vasorum and Crenosoma vulpis. Both are metastrongyloid nematodes transmitted through the same intermediate hosts, both infect dogs and foxes, and both cause respiratory signs. Yet the diseases are clinically distinct in important ways — and getting the diagnosis right matters, because the severity, systemic complications, and urgency of treatment differ considerably between them.
What Is Crenosoma vulpis?
Crenosoma vulpis is a nematode that parasitises the bronchi and bronchioles of definitive hosts, principally foxes and domestic dogs. Unlike A. vasorum, which inhabits the pulmonary arteries and right ventricle, C. vulpis lives in the conducting airways themselves. This anatomical distinction largely explains why C. vulpis infection tends to cause more straightforward respiratory signs with fewer systemic complications — though it should not be underestimated as a cause of significant morbidity.
Geographic Distribution
Crenosoma vulpis is reported in North America, Northern and Central Europe, and the UK, with prevalence figures in fox populations suggesting it is more common than clinical case reports in dogs would imply. Its true prevalence in domestic dogs is likely underestimated due to diagnostic limitations and the tendency to investigate for A. vasorum rather than C. vulpis when lungworm is suspected.
Life Cycle
Adults in the airways produce eggs that hatch rapidly to L1 larvae, which are coughed up, swallowed, and passed in faeces. Slugs and snails act as intermediate hosts, ingesting larvae from contaminated soil and developing them to the infective L3 stage. Infection in dogs occurs through ingestion of infected molluscs. The prepatent period is approximately three weeks — considerably shorter than that of A. vasorum.
Clinical Signs of Crenosoma vulpis Infection
The predominant and often sole clinical sign of C. vulpis infection is coughing. This may be chronic, persistent, and productive in character, sometimes described by owners as a deep, harsh cough or apparent attempt to clear the throat. Affected dogs may produce mucus or foam when coughing. Exercise intolerance and mild dyspnoea can accompany severe infections.
Crucially, the systemic complications that define severe A. vasorum infection — coagulopathy, haemorrhage, neurological signs, and cardiac involvement — are not features of C. vulpis infection. A dog with an isolated chronic cough, without bleeding, neurological signs, or evidence of right-sided cardiac compromise, is considerably more likely to be harbouring C. vulpis than A. vasorum, particularly if the cough is the presenting and only complaint.
Differential Diagnosis: Crenosoma vs Angiostrongylus
Distinguishing these two parasites is clinically important and requires systematic evaluation.
Clinical Features That Help Differentiate
- Coagulopathy or unexplained bleeding strongly favours A. vasorum; it does not occur with C. vulpis
- Neurological signs — seizures, ataxia, spinal haemorrhage — point to A. vasorum
- Isolated chronic cough as the sole presenting sign is more consistent with C. vulpis
- Right-sided cardiac changes on echocardiography suggest A. vasorum
- Pulmonary arterial changes on radiography or CT favour A. vasorum; airway-centred changes may be seen with either
Laboratory Differentiation
Both parasites can be detected using the Baermann technique on fresh faeces, but the larvae are morphologically distinct. L1 larvae of C. vulpis have a longer, more sinuous tail tip compared to those of A. vasorum, and experienced parasitologists can differentiate them on morphometric examination. In practice, many general practices now use commercial antigen tests, which are typically specific to A. vasorum; a negative antigen test in a coughing dog does not exclude C. vulpis. PCR-based faecal testing, available through specialist diagnostic laboratories, can differentiate species reliably and should be requested where species identification will affect management decisions.
Bronchoalveolar Lavage
Bronchoscopy with lavage may reveal larvae or eggs in the airway fluid and is particularly useful in cases with negative faecal results where clinical suspicion remains high. The eosinophilic or mixed inflammatory pattern in lavage cytology is non-specific but supportive of parasitic bronchitis.
Treatment
Macrocyclic lactone products used for A. vasorum treatment are also effective against C. vulpis, and the two infections are generally managed with the same drug classes. The key practical difference is that the urgency of treatment is typically greater with A. vasorum due to the risk of fatal haemorrhage or acute respiratory failure. Dogs with C. vulpis infection are rarely in immediate danger, though untreated cases can develop chronic airway inflammation and secondary bacterial bronchitis.
Coagulation testing, blood pressure assessment, and thoracic imaging are warranted whenever A. vasorum cannot be excluded. If the diagnosis is uncertain and the clinical picture could be consistent with either parasite, treating empirically for both — under veterinary supervision — is a reasonable approach given that effective drugs overlap.
Prevention
Products licensed for A. vasorum prevention in the UK also prevent C. vulpis infection. Monthly macrocyclic lactone preventatives are therefore appropriate for dogs at risk from either or both parasites — particularly those living in areas with significant fox populations or those known to investigate and eat garden invertebrates.
Summary: Telling These Two Lungworms Apart
- Both C. vulpis and A. vasorum are transmitted through slugs and snails and occur in UK dogs
- C. vulpis lives in the airways; A. vasorum lives in the pulmonary arteries and heart
- C. vulpis causes chronic cough; A. vasorum causes cough plus potential bleeding, neurological signs, and cardiac disease
- Standard A. vasorum antigen tests do not detect C. vulpis — species-specific PCR or larval morphology is required for confirmation
- Both infections respond to macrocyclic lactone treatment
- Monthly preventative products protect against both parasites
- Consult your veterinarian if your dog has a persistent cough, particularly if they are known to eat slugs or snails
A persistent cough in a dog should never be dismissed as trivial. In an era when two potentially serious lungworm species circulate in UK fox and dog populations, it warrants proper investigation — and, ideally, prevention before it is needed.