Brownsea Red Squirrels

About Squirrel leprosy

What is squirrel leprosy?

Early exploratory tests have found that a particular type of  mycobacteria - the same as that which causes leprosy in humans - is present within the red squirrel population on Brownsea Island and is causing some of the squirrels to have obvious skin disease. Affected squirrels mainly have hair loss and swelling of their ears, muzzle and feet.

The disease is widespread. Red squirrels elsewhere in the UK have also been found to be affected with this disease, but the bacteria causing it has only recently been identified. Confirmed cases of the disease has been found in Scotland[1] and on the Isle of Wight[2].

Is there a risk to humans?

We understand that the risk to human health is negligible. The bacteria that cause leprosy cannot survive outside the body and evidence shows that 95% of all adults are naturally unable to get leprosy, even if they are exposed to the bacteria that causes it. Taking sensible precautions such as avoiding physical contact with wild animals and washing your hands before eating will further minimise any risk.

What are the symptoms found in squirrels/how does it affect them?

Symptoms include crusty, thick skin on the ears, which can lead to swellings that resemble ‘cauliflower’-like ears. Warts or bulbous swellings may be seen on the face, particularly around the eyes and bridge of the nose.

What risk is there to other wildlife (including pets, such as cats and dogs)?

It is possible that the disease is transferable to other small and mid-sized mammals. This is something that we will be exploring as part of the initial detailed risk analysis with Edinburgh University and through the doctoral research.

How is the disease transferred to other species?

We do not currently understand how – or even whether – the disease can be transferred either between squirrels or between other species. If it is transmitted in a similar way to in humans, it is likely to be through prolonged contact with secretions such as saliva or nasal discharge or by breathing in aerosols created by coughing or sneezing.

Brownsea Island

What are you doing to find out more about the disease?

National Trust and Dorset Wildlife Trust – the two nature conservation organisations working on Brownsea Island – are supporting research by University of Edinburgh to better understand how leprosy affects and is spread among British red squirrel populations. The findings will help nature conservationists in the UK confront this disease.

The research will have two stages:

  1. Initial research into the nature and scale of leprosy in red squirrel populations on Brownsea Island. Expected to last a year (to Spring 2017), this research will also explore whether the disease has been transferred to/from other rodent species on the island. The research will help inform managers on Brownsea about any potential risks to visitors and wildlife.
  2. A doctoral research project, beginning in September 2016, will look at the scale of the threat to red squirrel populations across the UK, identify ways that conservationists can tackle the disease and address risks of the disease being passed between wild species.

What steps has the National Trust and Dorset Wildlife Trust taken to inform visitors and other stakeholders about the disease?

We have informed those who regularly visit the island for professional reasons, including National Trust and Dorset Wildlife Trust staff and volunteers, other organisations and contractors. We have informed the relevant local and national government authorities. Leprosy in wild animals is not a notifiable disease.

Visitors will be informed via information on the website and upon arrival on the island about sensible hygiene practice when dealing with wild animals and birds.

Do visitors to the island need to take any precautions, and if so what?

As with all wild animals, particularly those wild animals that are dead or sick wild animals, we advise that visitors do not handle any that they find.

Would you consider culling the red squirrels?

There is no plan to cull red squirrel population on Brownsea. The red squirrel population on Brownsea Island has had this disease for at least 30 years. It is likely that most squirrels are healthy and may be resistant to the disease.

How long have you known that Brownsea’s red squirrels have this disease?

We are aware that a few of the red squirrels on Brownsea Island have sometimes shown symptoms of the disease for at least the last 30 years. Deceased squirrels have been sent for analysis by government scientists, with tests identifying the disease as a form of pox virus.

Last summer Professor Meredith, who has been carrying out research on red squirrels in Scotland with this disease, saw a picture of one of Brownsea Island’s diseased squirrels and suspected it was a form of leprosy. 

We have since sent deceased squirrels from the island to be tested in a laboratory specialising in identifying this disease out find out more about the strain of mycobacteria that is affecting them.

What is the size of the squirrel population on Brownsea Island?

Ideal density of population is approximately 2 squirrels per hectare of land, depending on available natural food sources available within the habitat. The current population is believed to average out at 200 individual red squirrels, although numbers fluctuate as is common with an island population.

How long have there been red squirrels on Brownsea Island?

Records are patchy, so we do not know precisely how long the red squirrels have been present on Brownsea. Recent research by Bournemouth University shows that the Brownsea squirrels’ DNA is consistent with them originating in the south west of England (i.e. not introduced from elsewhere in the UK or Europe).

How many squirrels have the disease?

So far, of 23 deceased squirrels tested, around a third had obvious symptoms of leprosy but nearly all of them showed evidence of exposure to the bacteria. It is therefore likely that some squirrels can have the infection but do not get ill from it and/or the disease may take a very long time to develop, as it does in humans.

How many squirrels have died of the disease?

This is not something that we know. It is unlikely that leprosy directly kills squirrels; rather, the disease weakens the immune system so that death from other natural causes becomes more likely.

Will visitors to the island see, or come into contact with the infected squirrels?

It is highly unlikely that visitors will have physical contact with red squirrels; as with other wild animals, we would recommend visitors avoid touching the squirrels.

It is possible that visitors will see infected squirrels. As the disease is suspected of being in the population for some time, it is likely that this has always been true for visitors coming to Brownsea to see squirrels.

Can and will you treat the red squirrels?

The red squirrel population has suffered from this disease for at least 30 years and every year only a small handful of red squirrels are affected. We believe that many of the squirrels have built up an immunity of their own. Unfortunately it is practically impossible to treat the population of squirrels, would be cost prohibitive and not in the best interests of animal welfare.

Why is it impossible to treat the population of squirrels?

It would be practically impossible to treat the squirrels as it is likely that, as in humans, a course of up to three different antibiotics would need to be given daily by mouth for at least six months. It would not be possible to administer to wild free-living squirrels reliably or without a risk of other wildlife being exposed to the antibiotics. It would also not be possible or in the best interests of squirrel welfare to bring them into captivity for such a long time for treatment, and there are legal constraints on doing this.

To ensure a more sustainable population on Brownsea, we think that it is better to let nature take its course, with the genes from the naturally resistant squirrels becoming dominant.

Are you planning to vaccinate squirrels against the disease?

As part of the research project will be investigating whether vaccination may be possible, but as yet there is no specific leprosy vaccine available for either humans or animals. The disease is likely to be widespread, meaning that vaccinating the squirrels would have little effect.

What are we doing to prevent the spread of the disease?

As an island Brownsea is relatively isolated, limiting the spread of the disease to the mainland. The research with Edinburgh will identify potential risks of the disease being spread by other mid-sized mammals (such as Sika Deer).

Why has it taken so long for the disease to be identified in the red squirrel population?

In recent decades the spotlight has been on Squirrel pox caused by squirrelpox virus (SQPV). Squirrels with this virus can exhibit similar symptoms to those with leprosy. It was only when images of affected squirrels were examined by experts at University of Edinburgh that the true cause of the disease was identified.

Where else in the UK can you find red squirrels and are they affected by the disease?

Red Squirrels can be found on the Isle of Wight, central and northern Wales (including concentrated populations on Anglesey), at Formby on the Merseyside coast, in Cumbria and Northumberland. There are very small, isolated populations in the Cotswolds. Red squirrels are more widespread in Scotland; with approximately 120,000 squirrels (75% of the UK population).

In England, it is suspected that the strain of the disease identified in Brownsea’s squirrels is also present in populations on the Isle of Wight. Previous research by University of Edinburgh identified leprosy (caused by Mycobacterium lepromatosis) in squirrel populations in the Moray Firth, Scotland. (See Meredith, A., 2014, ‘Leprosy in Red Squirrels in Scotland’ JBVA 

How did squirrels pick up the disease in the first place?

This is not currently known. A PhD has been commissioned to try and understand how the disease came to be in the squirrel population at Brownsea.

How can members of the public help if they want to?

People can support the island and its squirrels by continuing to visit, volunteering to look after the island’s wildlife habitats or becoming members of either the National Trust or Dorset Wildlife Trust.

About the research

Why have the University of Edinburgh decided to use Brownsea Island a key site for their investigations, rather than studying local populations?

The project builds on previous and on-going studies focussing on disease risks to red squirrel populations. In addition to competition from grey squirrels, disease has been identified as a key threat to UK squirrel survival.

Leprosy is now known to be present on mainland UK, and the Isle of Wight, and its recent identification on Brownsea represents a unique opportunity to study the disease in a contained environment, acting as a model system to enable greater understanding into the dynamics and impacts of this pathogen disease.

The findings of the study may have implications for habitat management relating to optimum densities to maintain healthy populations and minimise disease transmission risks. It also may have significant implications for recommendations regarding supplementary feeding of red squirrels and monitoring methods using bait, as these create potential disease transmission foci.

About leprosy in humans

What are the symptoms of leprosy found in humans?

Leprosy affects the skin and nerves. It can also affect the eyes and the tissue lining the inside of the nerves. The main symptoms are pale skin sores or lumps that do not disappear after several months. Leprosy attacks the nerves outside of the brain and spinal column, leading to loss muscle weakness and of feeling in arms and legs.

How is leprosy transferable?

Transfer is through repeated contact with mouth or nose droplets from someone with untreated leprosy.

Can it be treated and are there any cases in the UK today?

Leprosy is easily treatable with antibiotics.

The Leprosy Mission report that the last case of indigenous leprosy (i.e. originating in the UK) was diagnosed in 1798, although currently around a dozen cases are diagnosed every year (with these originating overseas).


[1] Meredith, A., Del Pozo, J., Smith, S., Milne, E. (2014) Leprosy in red squirrels in Scotland. Veterinary Record 175: 285-286

[2] Simpson, V., Hargreaves, J., Butler, H. et al (2015) Leprosy in red squirrels on the Isle of Wight and Brownsea Island. Veterinary Record 177: 206-207


home  |  Living Landscapes  |  Living Seas  |  Jobs  |  e-news  |  Contact & Find Us | Web site Content Management