New strain of bird virus sweeps across Britain

01 Nov 2012 | No. 2012-44

A new strain of avian pox is taking its toll on garden birds in Britain, reports new research published this week in PLOS ONE.

Scientists from the Zoological Society of London (ZSL), University of Oxford, the British Trust for Ornithology (BTO) and RSPB report on the impact avian pox is having on great tit populations.

Avian pox has been recorded in British bird species such as house sparrows and wood pigeons for a number of years. However, the emergence of a new strain of this viral disease in great tits is causing concern amongst vets and ornithologists.

Wildlife vet Dr Becki Lawson from ZSL says: “Infection leads to warty, tumour-like growths on different parts of a bird’s body, particularly on the head around the eyes and beak."

“Although the disease can be relatively mild in some species, great tits suffer severe growths that can prevent them from feeding and increase their susceptibility to predation,”

Dr Lawson added.  "Whilst a range of tit species are susceptible to this novel form of the disease, detailed monitoring of birds in Wytham Woods by scientists at the University of Oxford show that great tits are by far the most susceptible."

Although recovery from infection can occur, our results show that this new strain of avian poxvirus significantly reduces the survival of wild great tits and has particularly large effects on the survival of juvenile birds,” says Dr Shelly Lachish of the Edward Grey Institute at Oxford University

Based on the numbers of affected great tits that we have observed at Wytham Woods, our models do not predict that this new disease will cause an overall population decline of the species. However, pox-affected populations have lower yearly growth rates. Hence, they are likely to have greater difficulty in recovering from other environmental factors that might reduce their numbers,” Dr Lachish added.

With help from the public, scientists at the RSPB and ZSL have tracked the disease, which has spread rapidly in five years from south-east England to central England and into Wales. The annual seasonal peak of observed cases occurs in the early autumn months and incidents continue to be reported at this time of year.

Genetic studies on the virus show that it appears to be the same strain seen previously in Scandinavia and more recently in central Europe, and is unlikely to have originated within Great Britain. BTO data on bird movements confirms that great tits rarely migrate outside the country. The spread of the virus to Britain is, therefore, thought to have occurred through the arrival of an infected vector, such as a mosquito.

Funding from NERC (the Natural Environment Research Council) enabled the detailed research reported here, and scientists are continuing to work together to monitor impacts of this new avian poxvirus strain on the population of great tits in the UK. They are calling on the public to assist in these efforts by reporting any signs of disease in garden birds to the RSPB, and have also highlighted that avian pox is not known to be infectious to humans or other mammals.

Notes for Editors

  1. Sightings of birds displaying symptoms of avian pox should be reported to the RSPB Wildlife Enquiries Unit preferably online via: or by telephone on 01767 693690.
  2. Avian pox is caused by avian pox virus.  Affected birds develop warty or tumour-like growths, on the head (particularly next to the eye or beak), legs, wings, or other body parts. The growths are usually grey, pinkish, red or yellow in colour. 

    Whilst a range of species are known to be susceptible to avian pox infection (e.g. house sparrow, wood pigeon, dunnock, starling), the recent cases of infection in tits are not typical of the type of avian pox we are used to seeing because the lesions are particularly large. In most cases lesions are distributed on the head around the eyes and beak. The extent to which different bird species are susceptible to different avian pox virus strains is unknown.

    The virus is spread between birds by biting insects that carry the virus, direct contact with other birds and indirect contact, possibly through contaminated bird feeders. Avian poxvirus is not known to be infectious to humans or other mammals.

    Although large pox growths can be very characteristic, smaller or medium-sized growths can easily be confused with a number of other conditions, such as ticks. The disease can only be confirmed by further investigation, such as post mortem examination and subsequent laboratory tests.

    Whilst supportive treatment can be attempted in captive birds, effective treatment of free-living birds under field conditions is not possible. Maintaining optimal hygiene at feeding stations can help to prevent outbreaks of disease. Where disease outbreaks occur, temporary removal of supplementary food may be appropriate to reduce close congregation of birds and reduced the risk of further disease transmission.

    For further information:
  3. Founded in 1826, the Zoological Society of London (ZSL) is an international scientific, conservation and educational charity: our key role is the conservation of animals and their habitats.  The Society runs ZSL London Zoo and ZSL Whipsnade Zoo, carries out scientific research at the Institute of Zoology and is actively involved in field conservation overseas. For further information please visit
  4. University of Oxford.  The Edward Grey Institute is research institute in the Department of Zoology at the University of Oxford, and conducts research into the ecology, behaviour, evolution and conservation of birds in their natural environments. For further information on the Edward Grey Institute at the University of Oxford, please visit:
  5. The British Trust for Ornithology (BTO) The BTO is the UK's leading bird research organisation. Over thirty thousand birdwatchers contribute to the BTO's surveys. They collect information that forms the basis of conservation action in the UK. The BTO maintains a staff of 100 at its offices in Norfolk,  Stirling and Bangor, who analyse and publicise the results of project work. The BTO's investigations are funded by government, industry and conservation organisations.For further information, please contact: Mike Toms, Head of Garden Ecology, t: 01842 750050, Email: mike.toms [at]
  6. The RSPB speaks out for wildlife, tackling the problems that threaten our environment. The RSPB has more than one million members, over 13,500 volunteers, 1,300 staff, more than 200 nature reserves, 10 regional offices, four country offices... and one vision - to work for a better environment rich in birds and wildlife.   the results of project work. The BTO's investigations are funded by government, industry and conservation organisations.

Contact Details

ZSL: Smita Chandra
Office: 020 7449 6288
Email: smita.chandra [at]

University of Oxford: Pete Wilton
Office: 01865 283877
Email: pete.wilton [at]

BTO: Paul Stancliffe
Office: 01842 750050
Mobile: 07585 440910
Email: paul.stancliffe [at]
(ISDN line available)

RSPB: Wendy Johnson
Office:  01767 693489
Email: wendy.johnson [at]

Interviews: Available on request

Lawson, B., Lachish S., Colvile, K.M., Durrant, C., Peck, K.M., Toms, M.P., Sheldon, B.C., Cunningham, A.A. Emergence of a novel avian pox disease in British tit species. PLOS ONE (In Press).

Lachish, S., Lawson, B., Cunningham, A.A., Sheldon, B.C. Epidemiology of the emergent disease Paridae pox in an intensively studied wild bird population. PLOS ONE (In Press).

Lachish, S., Bonsall, M.B., Lawson, B., Cunningham, A.A., Sheldon, B.C. Individual and population-level impacts of an emerging poxvirus disease in a wild population of great tits PLOS ONE (In Press).

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