British garden bird disease spreads to Europe

01 Sep 2011 | No. 2011-35

A deadly disease, responsible for a sudden decline in two familiar British garden birds, has now spread to Europe.

Trichomonosis first emerged in British finches in 2005 and has since caused local declines in populations of greenfinch and chaffinch, with greenfinch populations in some counties dropping by a third within a year of the disease emerging.

Research carried out by the Zoological Society of London (ZSL), British Trust for Ornithology (BTO) and University of East Anglia (UEA), and a number of other leading scientific organisations across Europe, now suggests that chaffinches migrating from British shores to Fennoscandia transported the parasite responsible for causing the disease.

Large numbers of chaffinches spend the winter in Britain before taking flight from the eastern shores of England to breeding grounds in Fennoscandia every spring. Only small numbers of greenfinches migrate to Europe, framing chaffinches as the most likely transporters of the disease.

The research team carried out comparative molecular analysis on the parasite and found no difference between the parasite in European and British finches. Recent research has already revealed that finch species in Britain carry the same strain of the parasite.

Dr Becki Lawson, wildlife veterinarian at ZSL says: “Understanding emerging infectious diseases and how they’re spread is essential if we’re going to protect people and wildlife in the future.”

Dr Rob Robinson from BTO says: “Information derived from ringed birds continues to provide crucial insight into behaviour, ecology and disease, as seen in this case with trichomonosis. This in turns plays an important role in the conservation of many of our best-loved garden birds.”

Dr Kevin Tyler from the UEA says “Molecular tools pay a vital role in identifying sources of emerging infectious diseases. In the case of trichomonosis in finches, we believe that the disease is most likely to have originated in British pigeons or doves.”

Birds suffering from trichomonosis often look lethargic and have fluffed-up feathers. They may also show signs of struggling to feed and have trouble breathing. The disease can occur at any time of the year but tends to peak during August and September.

The next research priority is to understand the spread and impact of this disease on bird populations across Europe.

Notes for Editors

  1. Evidence of spread of the emerging infectious disease finch trichomonosis,by migrating birds. Published in EcoHealth on Thursday 22 September 2011 (DOI: 10.1007/s10393-011-0696-8)

    A clonal strain of Trichomonas gallinae is the aetiologic agent of an emerging avian epidemic disease. In press in Infection Genetics and Evolution (DOI:10.1016/j.meegid.2011.06.00

    Copies of the above papers are available on request from the ZSL Press Office.
  2. Trichomonosis

    Trichomonas gallinae is a parasite of birds and does not pose a health threat to humans or mammals such as dogs and cats. The parasite has the potential to affect captive poultry and pet birds.

    Trichomonas gallinae, the cause of the disease, is a protozoan parasite (not a virus). Trichomonas typically causes disease at the back of the throat and in the gullet. Trichomonas gallinae is well known as a cause of disease in pigeons and doves, and birds of prey that feed on them. In 2005, trichomonosis was first recognised as a cause of disease in British finches. The greenfinch (Carduelis chloris)as been most frequently affected; the chaffinch (Fringilla coelebs) is the second most frequently affected species, although a range of garden birds have been found to be susceptible to the parasite.

    Trichomonas is vulnerable to desiccation and cannot survive for long periods outside the host. Transmission of infection is most likely to be through birds feeding one another with regurgitated food during the breeding season; or through food or drinking water contaminated with saliva. Trichomonosis outbreaks are most severe and frequent in the period of August to October. Sick birds are often obvious, as they have a tendency to stay close to feeders and water sources, and often die there. Lack of birds in the garden without the presence of sick or dead birds does not indicate a disease outbreak, but is most likely caused by the seasonal changes in birds’behaviour in late summer and autumn.

    Sightings of birds displaying symptoms of trichomonosis can be reported to the RSPB online via:

    For further information including a disease fact sheet with information on prevention and control of trichomonosis outbreaks:

    Information on bird ringing, including online reports of which birds move where and when,can be accessed at:

    This research is an output of the Garden Bird Health initiative, a collaborative project funded by the following organisations; Birdcare Standards Association, British Trust for Ornithology, British Veterinary Association Animal Welfare Foundation, CJ Wildbird Foods,Cranswick Pet Products, Defra, Gardman Ltd., RCVS Trust, RSPB, John and Pamela Salter Trust, Tom Chambers Ltd., and the Universities Federation for Animal Welfare.

    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

Contact information

Mike Toms
BTO Head of Garden Ecology
Office: 01842 750050
Email: mike.toms [at]

Victoria Picknell
ZSL Press Office
Office: 0207 4496361
Email: victoria.picknell [at]

Interviews: Interviews with the authors are available on request

Images: High resolution images are available on request

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