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Avian Disease Overseas: trichomonosis and British garden birds
Since 2005, I have coordinated the Garden Bird Health initiative, a research project to help us learn more about the diseases that affect garden birds across Great Britain. My role involves performing post mortem examinations on wild birds in the laboratories at the Institute of Zoology, based at ZSL London Zoo.
This work has been dominated by the emergence of finch trichomonosis in 2005. We have been investigating the outbreaks of this disease which have occurred each year in the late summer months. The parasite has led to significant regional declines of common wild finch species within a short time frame, overall we estimate that over half a million birds died during the 2006 epidemic alone.
In the late summer of 2008 I met with vets from Finland, Norway and Sweden who had recently received reports of disease outbreaks, particularly involving greenfinches and chaffinches. These government veterinary centres have monitored wild bird health for many years but this was the first time that they had recorded cases of this disease. It seemed likely that these events were linked, given that the species were similar to those we have seen affected in Britain, and the disease was novel in both countries. To confirm, we imported parasite DNA collected from finches in Fennoscandia with the disease and performed a series of molecular tests. We found no difference between the sequence data from Fennoscandian and British finches.
Information on bird migration collected over the past 30 years through the work of licensed ringers and reports by members of the public was then reviewed by ornithologists. The evidence points to migrating chaffinches as the most likely route of spread of the parasite from Britain to Fennoscandia. Specifically we think that infected chaffinches left the east of England in the spring of 2008 and returned to their summer breeding grounds in southern Fennoscandia taking the parasite with them.
So what happens during a post mortem?
Trichomonosis causes ulcers to develop in the gullet of affected birds so we carefully examine the digestive tract as part of the post mortem examination. Since the ulcers interfere with the birds’ ability to swallow normally, the birds can often have food and saliva staining of the plumage on their face and are typically in poor body condition. If lesions are present, we take samples in a specialist broth to try and culture the parasite which takes up to five days. We also take a duplicate frozen sample which we can use to extract the parasite DNA and confirm the diagnosis with a molecular test. Since the birds are small this can be very delicate work!
Who is involved?
This kind of investigation is a collaborative effort on an international scale. Vets, ornithologists, molecular biologists, volunteers and even the general public all contribute. A network of volunteers from the British Trust for Ornithology’s Garden Bird Watch have been monitoring the birds in their garden on a weekly basis and let us know if they spotted anything unusual. Additionally, the RSPB wildlife enquiries unit also provides a hotline for people to call if they have concerns about their garden birds, so they will alert us to any suspected cases of trichomonosis.
Both the greenfinch and chaffinch populations are widely distributed across Europe; over the next year we hope to form a European network of vets and ornithologists so that we can track the spread and impact of this finch trichomonosis on wild bird populations.
Emerging infectious diseases are increasingly recognized as a threat to wildlife populations that can adversely affect animal welfare and cause population declines in some cases so can be important for species biodiversity and conservation. We hope that our investigations will help us learn more about the origin and long term impact of this parasite and inform methods to help mitigate its spread in the future.
- To report sightings of birds displaying symptoms of trichomonosis please visit the RSPB website: http://www.rspb.org.uk/advice/helpingbirds/health/sickbirds/greenfinches.aspx