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Systematic assessment of the impact of adenovirus infection on a captive reintroduction project for red squirrels (Sciurus vulgaris)
  1. D. J. Everest1,
  2. C. M. Shuttleworth, PhD2,
  3. S. S. Grierson, PhD1,
  4. J. P. Duff, BSc, MSc, MVB, MRCVS3,
  5. N. Jackson, MBE4,
  6. P. Litherland4,
  7. R. E. Kenward, DPhil, DSc5 and
  8. M. F. Stidworthy, MA, VetMB, PhD, FRCPath, MRCVS6
  1. 1AHVLA – Weybridge, Woodham Lane, New Haw, Addlestone, Surrey KT15 3NB, UK
  2. 2Red Squirrel Survival Trust, Plas Newydd Country House, Llanfairpwll, Anglesey LL61 6DQ, UK
  3. 3AHVLA – Penrith, Merrythought, Calthwaite, Penrith, Cumbria CA11 9RR, UK
  4. 4National Zoological Society of Wales, Welsh Mountain Zoo – National Zoo of Wales, Colwyn Bay, Conwy LL28 5UY, UK
  5. 5Centre for Ecology and Hydrology, Benson Lane, Crowmarsh Gifford, Wallingford OX10 8BB, UK
  6. 6International Zoo Veterinary Group, Station House, Parkwood Street, Keighley, West Yorkshire BD21 4NQ, UK
  1. E-mail for correspondence: david.everest{at}

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PCR was used to amplify adenoviral DNA, and transmission electron microscopy (TEM) to detect adenovirus particles in tissue and intestinal content samples from red squirrels (Sciurus vulgaris) associated with a reintroduction study on Anglesey (North Wales), from other populations on the island and from stock held at the Welsh Mountain Zoo, 38 km to the east. Samples were collected during the routine surveillance postmortem examinations of all 60 red squirrels with carcases retrieved in a suitable condition between 2004 and 2010, including 29 captive and 31 free-living animals. Following significant clusters of mortality in captive red squirrels, adenovirus was identified retrospectively in faecal material from 12 of 13 (92 per cent) examined carcases from squirrels captive on Anglesey, and 14 of 16 (88 per cent) from the Welsh Mountain Zoo. Virus was identified in 13 of 31 (42 per cent) free-living wild animals, with evidence of both subclinical and clinically significant enteric adenoviral infections in wild squirrels. Without ancillary PCR and TEM testing, the extent of adenovirus infection in such populations would have been underestimated. Screening protocols that include examinations for adenovirus should, therefore, be part of the routine biosecurity measures protecting reintroduction or captive breeding programmes for red squirrels.


The native red squirrel (Sciurus vulgaris) has been replaced across large parts of Great Britain by the larger introduced North American eastern grey squirrel (Sciurus carolinensis). Grey squirrels compete directly with red squirrels for resources (Kenward and Holm 1993), lowering juvenile recruitment rates (Wauters and others 2000; Gurnell and others 2004) and acting as a reservoir for infections such as squirrelpox virus (SQPV), which causes fatal disease in red squirrels in the wild (Rushton and others 2006; Atkin and others 2010). Potential impacts of SQPV upon local and regional red squirrel populations are being increasingly understood (Sainsbury and others 2008). …

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