Avian pox in garden birds
5 November 2012
Avian pox is a viral skin infection that shows up as unsightly growths on the affected bird, mainly on the head and neck, and at the base of wings.
Which birds are affected?
Avian poxvirus infections have been recorded from British garden birds for many years, mainly in dunnocks, house sparrows, starlings and wood pigeons. However, Since 2007, we have received reports of pox lesions in tits, mostly in great tits, particularly during the late summer and autumn months. It is common for a number of tits to be affected in one garden, and their lesions can be quite severe.
The extent to which different bird species are susceptible to different strains of avian poxvirus is unknown. However, the disease could potentially be infectious to poultry, cage and aviary birds. Avian pox is found only in birds, and so it does not pose a threat to the health of humans or other mammals.
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 pinkish, red, yellow or grey in colour. Affected birds often appear to feed and move around normally.
In many species (e.g. wood pigeons and dunnocks) the growths can be relatively mild and may regress with time. In some cases (in all species but especially in tits) the growths can become very large and may impede the ability of birds to see, feed or move around. In these cases the birds become more susceptible to predation, starvation and other infections.
Although large pox growths can be very characteristic, smaller or medium-sized growths can easily be confused with a number of other conditions, including ticks. The disease can only be confirmed by further investigation, such as post mortem examination and subsequent laboratory analysis.
While the disease in great tits is not always fatal – recovery can occur – the condition does reduce an individual’s chance of survival, especially of juvenile birds. Fieldwork and statistical modelling by scientists at the University of Oxford suggests that the virus is not expected to cause a widespread population decline of great tits at current infection rates, although in some instances it may have the potential to slow down or even prevent recovery from declines otherwise caused.
How is it passed on?
Avian poxvirus is thought to be spread between birds in three main ways:
- by biting insects (e.g. mosquitoes, mites and flies)
- by direct bird-to-bird contact
- by indirect contact via contaminated surfaces such as perches or bird tables.
The virus is relatively resistant and can persist on contaminated surfaces (perches, bird tables etc) for long periods of time.
Whilst cases can occur any time of the year, there is a pronounced seasonal peak in the late summer and early autumn months each year, coinciding with the season when biting insects are at their most active.
Where did the pox come from, and where is it found?
Cases of avian pox in species other than the tit family have been reported across Britain for a long time. The novel and severe form of the poxvirus in great tits was first seen in southeast England but has spread northward and westward since 2009. Currently, the infection has spread across England and Wales as far north as the line from the Mersey to the Humber. Since the great tit is a common species across Britain, continued northward spread can be expected in the coming years.
A form of avian pox in great tits has been recorded in Central Europe for some years before it appeared in Britain, and in Scandinavia as long ago as the 1970s. Genetic studies show that the virus affecting British great tits has an identical sequence to that in mainland Europe. In contrast, a number of different strains of the poxvirus are found in species other than tits in Britain.
We believe that the most likely explanation for the emergence of avian pox in British tit species is that the virus has been transported from Continental Europe to Britain. Rather than brought in by migrating birds, the most likely scenario is that insects carrying the virus were carried across the Channel on air currents, making landfall in southeast England.
What can I do?
Whilst supportive care can be attempted in captive birds, there is no treatment that could be given to free-living birds.
Where an avian poxvirus outbreak exists, general measures of disease control in wild bird populations should be adopted. Ensure optimal hygiene at garden bird feeding stations, paying particular attention to regular disinfection of surfaces that the affected birds have been in contact with, such as perches and feeder ports. Clean out bird baths on a daily basis, and refill with fresh water.
If a large number of sick birds congregate, consider reducing the amount you feed for up to a month to help reduce close contact between the sick and healthy birds.
If you keep domestic birds, you should prevent contact between captive and wild birds as much as possible; wash and disinfect your hands thoroughly after handling wild bird feeders or equipment, and reduce the exposure of your birds to biting insects where feasible.
How you can help us to help the birds
The RSPB, together with the Institute of Zoology, University of Oxford and the BTO, are investigating the spread and intensity of avian pox in the UK, and the full range of species affected by it. If you see any garden bird with growths, please report this to us. You can access a recording form by clicking on the link on the right.
If you have any photographs of the affected birds, it would be helpful if you could attach these to the report, as they will help us identify what may be causing the growths. Your contribution will be valuable for our monitoring work.
Please return the completed form to the RSPB Wildlife Enquiries team. If you require further information or advice, please e-mail Wildlife Enquiries at email@example.com or call 01767 693690 (Monday to Friday 9 am to 5 pm).
Garden Bird Health Initiative
The Garden Bird Health initiative (GBHi) was set up as a UFAW (Universities Federation for Animal Welfare) Working Group in 2003, including among others the RSPB, the BTO, and the Institute of Zoology.
In 2005, the GBHi was extended to become a major research and surveillance project studying garden bird health and disease outbreaks. This unique combination of scientists, conservationists and wildlife vets has proved to be a very successful partnership.
The group develops and publishes guidelines about how to best feed garden birds in order to maximise the benefits for their conservation and welfare, and minimise the risks from infections. It also researches the impacts of disease outbreaks on bird populations.