How are birds affected?
Avian pox virus itself varies in its effects on birds. It has long been known to be serious, often fatal, in canaries whereas avian pox infection of other species of bird, such as crows and pigeons, may be much milder. It all depends upon the strain of the virus, the species of bird and the susceptibility of the bird at risk.
The signs of avian pox therefore vary depending upon the factors above. However, the most prevalent sign is the presence of raised, rather “warty” growths, especially on the bird’s head and sometimes on its feet. The unfeathered parts of a bird seem to be particularly susceptible. Internal organs can also be affected, but this is rare.
Mild cases may pass unnoticed, but birds with pox lesions on the face may not be able to feed properly or, if the lesions are on the eyelids, will have limited vision or be blind and thus not feed. In the latter case, birds with pox die of starvation and dehydration. There is no specific treatment for avian pox but affected birds can be nursed and fed by hand; some will recover.
Is Avian pox a new concern?
Avian pox infection has been recognised in Britain, in both captive and free-living birds, for many decades and many scientific and papers have been written about it.
What is different – and probably significant – about the current outbreak is that it is affecting species of British bird that hitherto have not, apparently, been infected by avian pox. In particular, great tits (Parus major) have been affected. The first confirmed case in a British great tit was in 2006 but last year, 2010, the disease was reported in this species in Wytham Woods in Oxfordshire, a famous location for ornithological research, where great tits have been studied since 1947.
So what is being done about this disease?
Fortunately, two experienced teams of scientists are studying it and collaborating closely. One team is from the London Zoo (Zoological Society of London) and is led by Dr Becki Lawson, MRCVS, a veterinary surgeon who has specialised in wildlife diseases. The other team consists of professional ornithologists at the University of Oxford, at the world-renowned Edward Grey Institute. These vets and zoologists, working closely with birdwatchers, field naturalists and the public, are attempting to monitor the spread of avian pox and to learn more about it.
And what should those who feed wild birds or keep them in captivity be doing?
First of all, it is important that spread of avian pox is reduced to a minimum. The virus, which is very resistant, can spread from bird to bird by direct contact or from contaminated bird feeders or other places where wild birds congregate. Therefore, hygiene – the regular cleaning of surfaces with an appropriate disinfectant (or even hot soapy water) – is imperative. Water containers are a very likely cause of spread; these should always be kept clean and, particularly in the current, have the water replaced daily. Avian pox can also be spread by fighting insects, especially mosquitoes, and these are most likely to be active at this time of the year (late summer). Wild birds are often bitten by mosquitoes in the evening when they are starting to roost for the night.
3 steps to safer and more hygienic bird feeding:
- Keep clean! Regularly clean bird feeders & bird tables with disinfectant (Vanodine) or hot soapy water
- Water the birds! Replace water daily.
- Be clean! Always wash your hands after filling/cleaning feeders
Captive birds such as canaries, zebra finches and budgerigars that are kept indoors are unlikely to contract avian pox from wild birds although, certainly in theory, mosquitoes harbouring the virus may infect them. However, birds kept in outside aviaries may not only be bitten by bloodsucking insects but also come into contact with avian pox virus as a result of contamination by wild birds of the wire, perches or floor of their aviary. Once again, strict hygiene is important. This should, if feasible, be coupled with the covering of the top of aviaries to minimise direct contact with wild birds.
All members of the public, whether or not they feed or keep birds, should be aware of avian pox and be prepared to report it if they see possible cases. There are various internet websites on which such a report can be made; alternatively, the person who has seen what s/he thinks may be avian pox and prefers to speak to someone on the ‘phone should contact the Royal Society for the Protection of Birds (RSPB) Wildlife Enquiries Unit on 01767 – 693690.
Summary of important points.
- Avian pox, a disease of birds caused by a virus, appears to be spreading in Britain. There is particular concern about its effects on great tits (Parus major)
- Avian pox can affect many species of bird, but presents no obvious risk to humans.
- Typically, the disease is characterised by raised, wart-like, swellings on the head of the bird. These may cause its death by starvation.
- There is no specific treatment for this disease.
- Avian pox is spread from bird to bird by direct contact, from contaminated feeders and by the bite of mosquitoes and some other insects.
- Control of the disease in wild birds coming to feeders depends largely upon hygiene, to reduce the spread of the (very resistant) virus.
- Members of the public who think they have seen birds with avian pox are encouraged to report this.
Professor John E Cooper DTVM, FRCPath, FSB,CBiol, FRCVS
RCVS Specialist in Veterinary Pathology
Diplomate, European College of Veterinary Pathologists
European Veterinary Specialist, Zoological Medicine
5th August 2011