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Home > NIEA > Conserving Biodiversity > Northern Ireland Squirrel Forum > Squirrel Pox and other squirrel diseases

Squirrel Pox and other squirrel diseases

Last updated: 7 May 2013

Squirrel Pox

a photo of a dead red squirrel which has suffered from squirrel pox copyright Moredun Research InstituteThe squirrel pox virus, sometimes erroneously referred to as squirrel para-pox, is responsible for the disease known as squirrel pox which presents in red squirrels with a mange, scab or myxomatosis-like symptoms, leading to rapid loss of body condition and subsequently death.  The animal’s behaviour may change especially toward the end, they become lethargic and more approachable. The virus appears to be endemic amongst the UK grey squirrel population and its effects, if any, on this species are unclear.

Nearly all grey squirrels with pox antibodies do not display any outward symptoms. Pox-type viruses are fairly resilient and will survive outside the host for a considerable time if the conditions are favourable.  Dry weather may mean the virus remains viable for over a month.  Wet conditions will reduce its viable period considerably. Outside the host the virus can be killed by good hygiene procedures using anti-viral veterinary disinfectants. Once in a population of squirrels the virus spreads very quickly, isolated woodlands can quickly lose all their red squirrels.

The NISF has developed a Standard Operating Procedure (SOP) document that explains the best procedures for cleaning and disinfecting traps and squirrel feeders.

The photos show a red squirrel that has died of Squirrel pox, the animal has been severely visually impaired by the infection and will not have been able to feed itself once the disease advances, also note sores on the paws.

Despite being blamed, at least in part,  for the decline of the red squirrel in England and Wales, Squirrel Pox was not recorded in Ireland until very recently.  Squirrel Pox was first discovered in Northern Ireland at Tollymore Forest Park County Down during March 2011 and 3 months later in the Glenarm area of County Antrim. The reason for its sudden discovery in two locations within three months when it was not previously known in Ireland is unclear.

We suspect that it has always been present but the last severe winter may had lead to increased squirrel movements as they were looking for food and or more frequent visits to artificial feeding sites, which in turn lead to more contact between individuals especially as the grey squirrel population has continued to increase.

The exact mode of transfer of the virus between animals is unclear, but it is likely passed on directly from contact with body fluids such as saliva or scent gland secretions.  There is also the possibility that parasites such as mites, fleas or ticks play a role in the viruses spread.  

There is no known risk to Humans from Squirrel pox but washing your hands after handling any animal is advisable as other pathogens may potentially cause you harm.   

The picture below shows a red squirrel with the early signs of pox, swelling around the eyes, paws and mucus membranes.  

Notably the animal may only be affected down one side of its body, at least initially.  Squirrel with early signs of pox

The NISF has produced some guidance on the symptoms of Squirrel Pox as observed by members of the Tollymore Red Squirrel Group during the first half of 2011.  These guidelines can be viewed or downloaded here (pdf 1513Kb).

Logo for Queens University Belfast
Research by Queens University Belfast sponsored by the NIEA  looked into threat of squirrel pox to Northern Ireland's red squirrels.

The report published in February 2013 entitled  "Squirrelpox virus in Northern Ireland: quantifying the risk to red squirrels"

is available on our website here.  

  1. The collection of red and grey squirrel records from across NI (total 293) confirmed the results of previous studies that greys are widespread across the country whilst reds have become isolated and restricted.  
  2. They collected 208 grey squirrel carcases for tissue samples from across NI forty reds were collected as and where their carcases became available eg road kill.  
  3. Two distinct method were used:
    1. ELISA to establish the presence of antibodies (the animal has had the virus at some point in the past)
    2. qPCR to establish viral DNA (ie those that were actively infected)
  4. They were asked to test saliva, urine, faeces, and ectoparasites for the presence of the virus and hence determine their putative roles as vectors of the disease.  
  5. The number of grey squirrels actively infected with the virus was relatively low at 8%, however a higher proportion (22%) tested positive for the antibodies, indicating past exposure to the virus.  The distribution of seropositive squirrels was widespread, most forests with greys were positive for pox antibodies, however Belvoir Park Forest, Reburn (Holywood), Crawfordsburn, Killynether Wood (Scrabo, Newtownards) and Castlearchdale (Co. Fermanagh) had no past history of pox infection.  The absence of antibodies but the presence of virus in Crawfordsburn, Killynether Wood and Castlearchdale suggests the disease has recently spread to these areas.  Killynether is 8 Km north-west Mount Stewart, which hosts the remaining red populations in this part of County Down.  
  6. There was a trend for squirrel pox infection in greys to vary significantly between the seasons, ie being more prevalent in spring and summer than in winter.  This was in contrast to previous research by other scientists in 2010 which reported the opposite.  This was in line with what Colin McInnes from the Moredun Institute (Edinburgh) had stated to us \{NIEA\} in 2009 that the virus particles survived better in dry warmer conditions than wet colder conditions.  
  7. Virus DNA was found in faeces (ie environmental spread by diarrhoea etc) and saliva from the positive red samples from Tollymore but was absent from the faeces and salvia of positive grey squirrels.  This confirms our original thinking in the issuing of licenses to cull obviously infected red squirrels as likely vectors of the disease.  
  8. Virus DNA was detected in the urine of some grey squirrels.
  9. All fleas and ticks from the pox positive red and a third of ectoparasites from the pox positive greys tested positive for squirrel pox virus and this could well be a source of transmission of the disease.  
  10. Squirrelpox virus is indigenous to grey squirrels and is present in most populations throughout Northern Ireland. However, grey squirrels typically have low viral loads and recover from the disease. Forests with no history of squirrelpox infection (i.e. squirrels lacking antibodies) but where virus has been detected, appear to occur at interface areas between grey and red squirrel populations and pose the greatest epidemiological risk to nearby red populations. Killynether Wood, with its close proximity to the red population at Mount Stewart and the broader Ards peninsula, is particularly notable in this respect. Limiting the contact between the two species in this area, and others such as Ballycastle, Baronscourt and Castlearchdale, may provide one means by which to slow or prevent the spread of the disease to remaining red squirrels. In areas where the range of the two species overlaps, measures to reduce encounter rates are considered essential (McInnes et al. 2012).

Other Diseases

Red squirrels seem particularly suscepible to a range of other diseases, this is probably due to the fact they are in relatively isolated populations, geographically separated from neighbouring populations, which in turn probably restricts the local genetic diversity. There is certainly a risk that should an infection get into a isolated population that those squirrels can be severely reduced in number and there are not enough new squirrels from satellite populations to back fill the losses. The spread of most of these diseases rely on close contact between animals, therefore where squirrels are attracted to artifical feeding sites there is an increased risk of pathogens coming into contact the visiting animals. Where feeders are used by squirrels frequent disinfection as detailed above can reduce disease spread.