Virus Threatens Scotland’s Red Squirrels

The first case of a red squirrel in Scotland dying as a result of the squirrelpox virus has sadly been reported by Scottish Natural Heritage. The red squirrel (Sciurus vulgaris) is one of the most threatened species of mammal in the UK, and Scotland supports 75% of the UK’s remaining red squirrel population.

Squirrelpox virus was first detected in Scotland in invasive populations of non-native grey squirrel (Sciurus carolinensis) in May 2005. The competing grey squirrels carry the virus, showing no signs of disease, but when transmitted to the native red squirrel the virus is invariably fatal. Targeted grey squirrel control has helped prevent the progression of the disease to Scottish red squirrels until now.

Squirrelpox virus is known to be one of the significant factors in the catastrophic decline of red squirrels in the UK. The virus has caused the deaths of hundreds of red squirrels in England and, in February, a red squirrel died for the first time in Wales from the virus. Whilst searching CAB Abstracts for information, it was worrying to read that the rate of red squirrel replacement by grey squirrels is some twenty times faster in those areas where grey squirrels carry the virus1,2.

In February 2006, a conference on Red squirrel conservation in Scotland resulted in the preparation of The Scottish Red Squirrel Action Plan 2006-2011 which makes a number of recommendations for the long-term conservation of the species, including development of a vaccine against squirrelpox virus. Let’s hope the plan works.

To search CAB Abstracts comprehensively for squirrelpox virus, note the following variations of the virus name: squirrel parapoxvirus, squirrel poxvirus
(The virus was originally classified as a parapoxvirus but recent phylogenetic analyses suggests that this is incorrect3,4).

  1. Squirrel poxvirus: landscape scale strategies for managing disease. Gurnell, J., Rushton, S. P., Lurz, P.W.W., Sainsbury, A.W., Nettleton, P., Shirley, M.D.F., Bruemmer, C., Geddes, N. Biological Conservation, 2006, Vol. 131, No. 2, pp. 287-295.2.
  2. Disease threats posed by alien species; the role of a poxvirus in the decline of the native red squirrel in Britain. Rushton, S.P., Lurz, P.W., Gurnell, J., Nettleton, P., Bruemmer, C., Shirley, M. D., Sainsbury, A. W. Epidemiology and Infection, 2006, Vol. 134, No.3, pp. 521-533.
  3. A novel poxvirus lethal to red squirrels (Sciurus vulgaris). Thomas, K., Tompkins, D.M., Sainsbury, A.W., Wood, A.R., Dalziel, R., Nettleton, P.F., McInnes, C.J. Journal of General Virology, 2003, Vol. 84, No. 12, pp. 3337-3341.
  4. Genomic characterization of a novel poxvirus contributing to the decline of the red squirrel (Sciurus vulgaris) in the UK. McInnes, C. J. , Wood, A. R. , Thomas, K. , Sainsbury, A. W. , Gurnell, J. , Dein, F. J. , Nettleton, P. F. Journal of General Virology, 2006, Vol. 87, No. 8, pp. 2115-2125.

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