Angiostrongylus vasorum (canine lungworm)

I have just published a podcast on Angiostrongylus vasorum which you can find HERE. Coincidentally a couple of papers have recently been published in The Veterinary Record on this and I thought I would provide a summary of their main findings in this blog post for those who cannot access these papers. I won’t be commenting on methodology, just transcribing from their manuscripts!


So the first paper is:

Kirk L, Limon G, Guitian FJ, et al. Angiostrongylus vasorum in Great Britain: a nationwide postal questionnaire survey of veterinary practices. Vet Rec 2014. 175:118.

Their main aim was to explore whether the parasite has been spreading around Great Britain. They write: “Despite the increasing number of reports of canine angiostrongylosis, there has so far been no attempt to establish the distribution of infection in dogs on a nationwide scale and formally assess potential geographic clustering”.

Approach:

Postal questionnaire sent to 3950 small animal practices asking:

  • Number of cases diagnosed over preceding year
  • Whether diagnosis was based on clinical signs alone or supported by additional testing ** NOTE: they only then included data from practices that used additional testing to achieve diagnosis.

Data were aggregated by county
Significant clusters of practices with a high probability of seeing confirmed cases were identified
Cluster maps were produced to illustrate cluster locations and level of significance of each cluster

Results:

35.9% questionnaire return rate (1419)
Of these 31.3% were aware of A. vasorum occurring within a 5 mile radius
>20% practices reported at least 1 confirmed case in the preceding 12 months
Two significant clusters of practices reporting at least 1 confirmed case: one in south-east England, second in Wales
Relative risk of practices having at least 1 confirmed case: 4.42 in England, 4.95 in Wales

They acknowledge that “practices that had seen cases might have been more likely to respond to the survey, thereby increasing the apparent frequency of cases in regions where canine angiostrongylosis had been diagnosed”.

Their interpretation of their data is that infection is widespread in dogs in Great Britain including outside of previously reported endemic foci.

They suggest that possible reasons for expansion of areas in which the parasite is found include:

  • Increased density of final (domestic and wild animal) and intermediate hosts
  • Movement of dogs in and out of endemic foci

Possible reasons for detection of infection in areas in which it was previously unrecognised may also include:

  • Improved surveillance
  • Greater awareness among both pet carers and vets
  • Improved diagnostic methods

Parasite distribution is widespread but not uniform

Main conclusion:A. vasorum has spread beyond traditional endemic foci in Great Britain. There are clusters of infection in south-east England and south Wales. The infection is widespread in central England and patchy in northern England and Scotland.”

[It is noteworthy that this patchiness of A. vasorum distribution is not unique to Great Britain with a similar situation having been reported for example in Denmark, Germany, France, Italy and North America – references available on request!]

The second paper is:

Blehaut TRW, Hardstaff JL, Chapman PS, et al. Spatial, demographic and clinical patterns of Angiostrongylus vasorum infection in the dog population of southern England. Vet Rec 2014. 175:148.

The authors write “The objectives of this study were:

  • First, to provide insight into the spatial pattern of A. vasorum infection in dogs in south-east England;
  • Secondly, to investigate the association between selected host characteristics (age, breed and sex) and risk of angiostrongylosis; and
  • Thirdly, to investigate, in cases of angiostrongylosis, the association between host characteristics and clinical presentation.”

Approach:

Retrospective study of all dogs referred to the Queen Mother Hospital for Animals at the Royal Veterinary College (Hertfordshire, England) between April 1999 and July 2012 and subsequently diagnosed with angiostrongylosis (141 dogs).

Cases were compared with a control group of dogs referred to the internal medicine, cardiology and emergency service departments by practices that had also referred A. vasorum-infected dogs during the same period.

Cases were categorised into three groups based on clinical presentation: cardiorespiratory signs, haemorrhagic diathesis, and ‘other’.

Some statistical tests were done!

Results:

Risk of angiostrongylosis was higher for:

  • Younger dogs
  • Jack Russell terriers, cocker spaniels, springer spaniels, cavalier King Charles spaniels, and Staffordshire bull terriers

Cardiorespiratory: 48%
Haemorrhagic diathesis: 38%
Significantly more frequent in boxers, Staffordshire bull terriers, cocker spaniels
‘Other’, mainly neurological: 14%

A statistically significant cluster was identified in a 73 km radius area:

  • No significant differences were found for the ages, sex and breeds of the population within and outside of the cluster.

Interpretation:

They comment on the limitations of a retrospective study and the selection of cases and controls from a not just a referral hospital but only one such hospital.

That said they say:
“Similar to previous studies, younger dogs were significantly overrepresented among cases, which may be related to the existence of some protective immunity following infection.”

“Differences across breeds could be related to intrinsic breed characteristics or be an artefact if some breeds have been overrepresented as a result of the infection of certain kennels or breeding premises.”

“The spatial clustering of cases may reflect a genuine higher risk of infection in the area identified, which could be considered a hotspot for infection in the south east of England”. NOTE: the similar finding in the paper above about the south east of England.

Main conclusion: “In the population studied, younger dogs, dogs of certain breeds and dogs that lived within a 73 km radius area had a significantly higher risk of angiostrongylosis. Some breeds were found to be at a significantly increased risk of haemorrhagic diathesis.”

Separately, do also check out the map from Idexx showing locations in the UK from which cases testing positive with their Angio Detect Test have been reported.