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A tale of two squirrels

| May 11, 2018

Bark gnawing and stripping damage caused two squirrels Carpinus betulus (common hornbeam) by Sciurus carolinensis (North American eastern Grey Squirrel).

The two species of squirrel resident in the United Kingdom (UK) are Sciurus vulgaris (native European Red Squirrel) and Sciurus carolinensis (North American Eastern Grey Squirrel), the latter introduced as a fashionable addition to estates in the 1870’s. Its population of 2.5 million is spread over most of the UK and dwarves the 140,000 native Red Squirrels, which are pegged back into parts of Scotland and northern England, plus a few islands such as Anglesey (North Wales) and the Isle of Wight, off the south coast. The native Red Squirrel is now one of the nation’s most highly prized biodiversity icons, while the Grey Squirrel is regarded as an alien invasive species.

However, the tale of two squirrels has a ‘sting in the tail’, which recently came to light during archaeological research carried out by scientists at Cambridge University in England. It appears that squirrels infected with the bacterial pathogen (Mycobacterium leprae), which causes leprosy, may have brought the disease to England along Viking, fresh meat and fur trading routes. We are of course talking about native S. vulgaris because S. carolinensis would not arrive in Europe for another 1,000 years, first introduced into England in 1876.

A study published in the Journal of Medical Microbiology, found medieval leprosy cases in human remains in Eastern England including a pre-Norman female skull dated to 885-1015 AD, unearthed in a garden at Hoxne, Suffolk. Analysis of the bacteria revealed the female had been infected with the same strain of leprosy previously found on the skeleton of a man from the neighbouring County of Essex, who had lived as early as 415-545 AD. This suggests that the disease had persisted for centuries in the south-eastern part of Britain, probably arriving on the east coast. The same strain of the bacterium has been found in skeletal remains dating from the medieval period in Denmark and Sweden.
The last case of human leprosy in Britain was over 200 years ago, but a recent study revealed leprosy infection in Red Squirrels on Brownsea Island in the County of Dorset (southwest England). Genetic sequencing of the bacterial strain showed it to be closely related to that detected in the skull unearthed in Suffolk.

Lead author Sarah Inskip, Research Associate at St John’s College Cambridge, said: “It is possible that this strain of leprosy was proliferated in the South East of England by contact with highly-prized squirrel pelt and meat and traded by the Vikings at the time this woman was alive. Strong trade connections with Denmark and Sweden were in full flow in the medieval period, with Kings Lynn and Yarmouth (towns on the east coast of England) becoming significant ports for fur imports. It is questionable how long the bacteria could have survived on fur or meat, but it’s notable that squirrels were also sometimes kept as pets.”

With the Red Squirrel living happily on Brownsea Island, this might suggest the native Red is tolerant but perhaps the alien Grey Squirrel is not. However, that does not lead to a possibility of introducing leprosy-causing bacterium into the Grey Squirrel population to wipe out this forest pest, just as the myxomatosis virus was deployed against European Rabbit (Oryctolagus cuniculus) in the 1950’s and 1960’s.

This is an extract of the full article published in International Pest Control – January/February 2018 issue.

Read full article online on page 52

Dr Terry Mabbett*
*Director, Dr Terry Mabbett Consultants.

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