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Squirrels 'host Lyme disease bugs'

Published 21/04/2015

Grey squirrels host the bacteria responsible for Lyme disease, it has been discovered
Grey squirrels host the bacteria responsible for Lyme disease, it has been discovered

Grey squirrels are in the dock again - this time for harbouring a serious infection that can be spread to humans by ticks.

The American immigrant rodents already have previous convictions for decimating native red squirrel populations and damaging woodland by stripping bark from trees.

Now scientists have discovered that they host the bacteria responsible for Lyme disease, which if left untreated can lead to a chronic inflammatory disorder affecting the joints, nervous system and heart.

In the UK, Lyme disease is caused by four species of Borrelia bacteria carried by the deer or sheep tick, Ixodes ricinus, and transmitted to humans through its bite.

Birds and rodents are both thought to be the most important wildlife hosts of the bugs, but until now the role played by grey squirrels in their life cycle was unknown.

Scientists who tested 679 squirrels from across Scotland and the North of England in 2012 and 2013 found that grey squirrels frequently carried ticks, and could be infected by all four bacteria species.

Around 12% of the collected squirrels were infected, most commonly by a species of Borrelia usually found in birds.

Lead researcher Caroline Millins, from the Institute of Biodiversity, Animal Health and Comparative Medicine at the University of Glasgow, said: "Frequent infection of grey squirrels with bird strains of Borrelia was unexpected, and challenges our current understanding of host pathogen interactions for this zoonotic pathogen.

"We found quite different patterns and duration of infection in grey squirrels compared to native woodland rodent species. Grey squirrels become infected with whichever strains are circulating in the local area, and our models suggest that the duration of infection isn't life-long. In contrast, native rodents tend to develop chronic lifelong infections with strains of Borrelia that have adapted to these hosts.

"We can't say from this study whether grey squirrels lead to an increase or decrease in the number of ticks infected with Borrelia species in an area, but we have produced comprehensive baseline data that future studies could use to investigate this."

Results from the research are reported in the journal Applied and Environmental Microbiology.

Grey squirrels were introduced to the UK from North America between 1876 and 1929 and are officially regarded as an invasive pest. It is against the law to release a grey squirrel into the wild, or to free one that has been trapped.

Around 4% of ticks in the UK are believed to carry Lyme disease bacteria and pose a threat to humans.

The disease was first identified in Old Lyme, Connecticut, US, in 1975. Its most common symptom is a distinctive skin rash looking like a "target" or "bull's eye".

People infected may also experience flu-like symptoms, including a headache and muscle pains. Symptoms can start up to 30 days after being bitten by a tick.

The infection can be successfully treated with antibiotics and only proves serious if unrecognised and allowed to spread.

Ticks, small relatives of spiders and scorpions, can be found in woodland, heathland, moorland and urban parks, and sometimes even gardens.

They are most often picked up by walkers or people camping in the countryside. Experts advise that the best way to prevent Lyme disease infection is to check for ticks attached to the skin as soon as possible after walking or cycling through high risk areas.

Ticks should be removed carefully with tweezers, or ideally a "tick remover" available from veterinary clinics.

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