Learn about the symptoms and spread of trichomonosis, and which species tend to be affected.
Trichomonosis is a disease caused by the protozoan parasite Trichomonas gallinae. It has been recorded in a number of garden bird species. The disease is also known as ‘canker’ when seen in pigeons and doves, and as ‘frounce’ when seen in birds of prey. It has been known as a disease of cage birds for some time.
Trichomonosis first emerged in British finches in 2005 and has since brought about local declines in the breeding populations of Greenfinch and Chaffinch in various parts of Britain. The disease is widely acknowledged to be the causal factor in the rapid decline of the British Greenfinch population, which was first noted in the summer of 2006.
BTO research
BTO researchers, working alongside others involved in the Garden Bird Health initiative, used Garden BirdWatch and other data to establish the impact of this disease on Greenfinch and Chaffinch populations. The results of this work revealed a substantial population decline in those areas where disease incidence was greatest.
Further research was conducted by an international team of experts, including BTO scientists, analysing molecular, epidemiological and ringing data. This work found that the strain of trichomonosis present in the UK and in Fennoscandia was identical, and that bird migration, primarily of Chaffinches, was responsible for its spread.
More recently, BTO researchers have also investigated how factors like urbanisation and garden bird feeding stations influence the occurrence and impact of trichomonosis.
Read more about the history and spread of trichomonosis in finches
Trichomonosis first emerged in British finches in 2005, and the initial focus of the 2006 disease outbreak was in the central and western counties of England and Wales. However, examination of BTO ringing data, coupled with observations collected through the Garden Bird Health initiative's Systematic Surveillance Scheme, revealed that there was a pronounced shift in the geographical distribution of the disease towards eastern England in 2007.
This was then followed by the appearance of the disease in southern Fennoscandia, (notably SE Norway, Sweden and Finland) where trichomonosis was confirmed at several different sites in 2008. A comparative molecular analysis could find no difference between the parasites present in finches at the British and Fennoscandian sites, suggesting that the Fennoscandian parasites had the same origins as those in Britain.
An examination of BTO ring-recovery data suggests that migrating finches are the most likely mechanism by which the disease could have spread from Britain to Fennoscandia. The pattern of movements between the different areas where disease has been reported, suggests that it is Chaffinch rather than Greenfinch that is the likely vector. Our wintering Chaffinches are drawn from across Fennoscandia, while our Greenfinches tend to come from the more western parts of Fennoscandia, such as Norway.
While it is believed that Chaffinches migrate directly from Britain to Fennoscandia across the North Sea in the spring, the autumn migration route sees the birds move through Denmark, Germany, the Netherlands and Belgium before crossing the English Channel. Greenfinches make a direct crossing of the North Sea in both directions. Consistent with the hypothesis that the Chaffinch is the primary vector, we saw the emergence of finch trichomonosis in northern Germany in April 2009.
Pathology and disease spread
Trichomonas typically causes disease at the back of the throat and in the gullet. The disease may progress over several days or even weeks. Affected birds:
- show signs of general illness (lethargy, fluffed-up plumage);
- may show difficulty in swallowing or laboured breathing;
- may have wet plumage around the bill, and drool saliva or regurgitate food that they cannot swallow;
- may have a visibly swollen neck.
The trichomonad parasite is vulnerable to desiccation (drying out) and cannot survive for long periods outside of the host (the bird). Transmission is most likely to be through contaminated food or water, e.g. where a bird with difficulty swallowing regurgitates food that is then eaten by another individual.
Trichomonas gallinae is a parasite of birds and does not pose a health risk to humans or their mammalian pets.
Species affected
Although known from pigeons, doves and birds of prey for some time, the disease came to prominence in the summer of 2005, when it was first noted in British finches. Epidemics of the disease occurred in 2006 and 2007, with smaller-scale mortality events noted in subsequent years.
Greenfinches and Chaffinches are the species that have been most frequently affected, but the disease has also been documented in other garden bird species, including House Sparrow, Dunnock, Great Tit and Siskin.
What you can do
- A few simple precautions will help limit the spread of disease in gardens and on feeders. Learn more about good garden feeding hygiene.
- Help us understand disease in wildlife by reporting any cases that you see. Information on diseases and other forms of mortality in garden wildlife is being collected through Garden Wildlife Health.
Report disease in your garden
Report sightings of diseased birds and other wildlife to the Garden Wildlife Health project: a partnership between ZSL, BTO, Froglife and RSPB.