Mortality in red squirrels (Sciurus vulgaris) associated with exudative dermatitis

Abstract

Red squirrels (Sciurus vulgaris) found dead or dying on the Isle of Wight and the island of Jersey were suffering from exudative, ulcerative dermatitis and superficial staphylococcal pyoderma. The principal gross lesions were on the lips, eyelids and feet and showed similarities to those of squirrelpox. The histopathological lesions were also similar and, although there was no ballooning degeneration of epidermal cells, intracytoplasmic inclusions resembling those seen in poxvirus infections were present. Examination of lesions by electron microscopy failed to identify any virions, and PCR analysis for squirrelpox virus proved negative. The skin lesions also resembled those of mange, but although numerous mites were present in the fur these were mostly Dermacarus sciurinus with small numbers of Metalistrophorus pagenstecheri. The occurrence of these species on red squirrels in Britain is confirmed, but neither is pathogenic and they were not considered to have been involved in the pathogenesis of the dermatitis, the primary cause of which was not established.

First report of dermatophilosis in wild European red squirrels (Sciurus vulgaris)

“…Similar opportunistic behaviour of Staphylococcus is reported among goats with dermatophilosis 9. Staphylococcus has been identified associated with exudative dermatitis cases in red squirrels in the UK 2. The predominance of D congolensis- like organisms in the deep layers of hyperkeratotic crusts and hyperplastic lesions suggests that this aetiology is significant in the pathogenesis, and thus it does not represent an opportunistic superinfection.…”

“…In red squirrels, the infection produces signs characterised by severe pustular dermatitis typically with the presence of Staphylococcus species. In the absence of SQPV, red squirrels are also found with an exudative ulcerative dermatitis associated with Staphylococcus aureus , the histopathological lesions sharing some clinical similarities with SQPV lesions2 and skin lesions due to Mycobacterium leprae and Mycobacterium lepromatosis infection 3. Cutaneous wart-like lesions have also been described affecting the pinnae and digits 4…”

Causes of mortality and pathological lesions observed post-mortem in red squirrels (Sciurus vulgaris) in Great Britain

“…All the S. aureus isolates were of the same lineage and all possessed the leukotoxin M encoding gene ( luk M). The lesions are described in more detail elsewhere [7,13]. …”

“…This condition is also a major cause of red squirrel mortality on the island of Jersey [7] and the S. aureus isolates from affected squirrels on both islands are of the same lineage and all encode the luk M gene [13]. The pathogenesis of the condition is not understood but it is invariably fatal.…”

“…Grey squirrels have colonised most of mainland England and Wales and red squirrels are now largely confined to north west England and Scotland with relict populations persisting on several islands which have been kept free of grey squirrels. Despite concerns that red squirrels may become extinct in Britain there has been only limited research into causes of mortality other than squirrelpox and much of the published data relates only to specific conditions [3-7]. Keymer [8] in 1983 was the first to describe the range of diseases affecting red squirrels in Britain but there were few comparable studies until 2010 when LaRose et al [9] conducted an extensive investigation in to causes of red squirrel mortality in Scotland.…”