Avian Influenza & Wild Birds: FAQs

 

Avian influenza is a highly contagious viral disease affecting many species of birds.  It is caused by a Type A influenza virus, which has 16 H subtypes and 9 N subtypes.  There are two forms of avian influenza virus defined by their pathogenicity to poultry; low pathogenic (LPAI) and highly pathogenic (HPAI).  Only viruses of the H5 and H7 subtypes are known to cause the highly pathogenic form of the disease in poultry – such HPAIs are of serious concern for the poultry industry.  A highly pathogenic form of the H5N1 virus is currently spreading across Eurasia and Africa, known as Asian lineage HPAI H5N1, and has caused enormous losses of poultry, and some mortality in wild birds and humans.    

 

Avian influenza circulates naturally in populations of waterbirds. A range of evidence suggests that wild birds can introduce low pathogenic H5 and H7 viruses to poultry flocks, which can then mutate to the highly pathogenic form. Under some circumstances HPAIs can then infect wild bird populations – contact between poultry and wild birds facilitates this exchange. Asian lineage HPAI H5N1 seems typically to cause high rates of mortality when it occurs in wild birds, but a study in SE Asia has shown that apparently healthy wild birds can carry the disease and shed viral particles – this is termed asymptomatic infection.     

 

Asian lineage HPAI H5N1 outbreaks in wild birds have resulted in mortality of infected birds followed presumably by rapid die-out of the infection in the wild.  However, more recent evidence of asymptomatic infection in wild birds suggests that some infected birds may be able to undertake normal movements, including seasonal migratory movements.  The appearance of Asian lineage HPAI H5N1 in wild Mute Swans (Cygnus olor) and its spread through parts of Europe in this species suggests that some Mute Swans are becoming infected and are then still able to move to new areas.  However, we still have limited evidence that other wild bird species have become infected and then carried the virus to new areas, although recent outbreaks in wild birds in Europe in the absence of prior infection in poultry strongly suggests that this is the case.

 

We cannot know with certainty how each outbreak of Asian lineage HPAI H5N1 has originated – there are a number of ways in which the virus could spread.  It is likely that H5N1 has spread through and beyond SE Asia primarily as a result of movements of infected poultry and poultry products, but some of the spread is probably also the result of movements of infected wild birds or cage birds.  However, the spread from Eastern Europe through to Western Europe appears to be linked to transmission by infected wild birds, particularly wild swans.

 

With the apparently high mortality rates seen in some wild bird species, the continued spread of Asian lineage HPAI H5N1 is of conservation concern.  It is estimated that in one outbreak in China, at Qinghai Lake, as much as 10% of the world's Bar-headed Goose population died.  There are a number of globally threatened waterbirds in Eurasia, with small populations, that would be at risk from enhanced mortality resulting from infection with HPAI H5N1. Implementation of high quality biosecurity around poultry would not only isolate poultry from possible infection by HPAI infected wild birds, but would help reduce 'spill-back' of the virus into other wild bird populations.

 

The World Health Organisation and UN Food & Agriculture Organisation have stated that the control of H5N1 by culling of wild birds is not feasible.  Culling of wild birds will not help prevent the spread of H5N1, rather disturbance to birds from culling activity could help spread the virus by dispersing any infected birds.  Similarly, destruction of wetland habitats is not only undesirable, but would be ineffective as a means of controlling HPAI in wild bird populations. Many governments around the world, including all EU Member States, have agreed, through their international commitments to bird conservation, that they will not cull wild birds in an attempt to control H5N1.  Defra has stated that it will not issue licenses for killing wild birds to control the spread of HPAI H5N1. 

 

Along with other European Union Member States, the UK government has imposed strict controls over the importation of poultry and poultry products and on the movement of cage birds.  Government has also been conducting surveillance for AI in wild birds, which is how the Cellardyke case was discovered in March 2006.  In response to the Cellardyke case in Scotland, the Government implemented its national contingency plan, which involves various restrictions within zones around an outbreak to limit further spread.  Defra also meets regularly with experts on bird migration and waterbirds to evaluate movements of birds – data from national bird surveillance schemes, such as the BTO/WWT/RSPB/JNCC Wetland Bird Survey and the British Ringing Scheme (organised by the BTO and part-funded by JNCC), are used to inform risk assessment of Asian lineage HPAI H5N1 both spreading and arriving at new locations within the UK as a result of wild bird movements. 

 

Government contingency plans set out measures that will be taken in the event of Asian lineage HPAI H5N1 occurring in poultry or wild birds – any restrictions on access to the countryside are likely to be localised.  Each case will be treated with local factors in mind. Access to the countryside via public rights-of-way will be controlled only if it is considered necessary to help prevent further spread of the disease or for human health reasons, and only for as long as it remains necessary to do so.  A government order may be made to restrict access via public rights-of-way to zones around infected areas and in such circumstances land owners and local communities will be informed and notices will be posted.  Any changes in access to National Nature Reserves will be in response to any local government orders; for more information contact your country conservation agency (Natural England, Scottish Natural Heritage, Countryside Council for Wales, or in Northern Ireland the Environment and Heritage Service).  You should continue to enjoy the countryside and parks as you normally do, but should observe any restrictions imposed by Government.

 

There is no need to stop feeding wild birds as long as you adopt sensible hygiene precautions – as a general rule you should not allow wild birds to touch you when feeding them as they can carry a number of disease that humans can catch.  For more information on hygiene and birds please see the Defra website and the garden bird pages of the BTO or RSPB  websites.

 

Wild birds are protected under law and it is an offence to kill or injure wild birds, to damage or destroy a nest while it is being built or in use, and to destroy or remove eggs from a nest.  Gardens are of high conservation value for many of our commoner birds, providing good nesting areas as well as essential feeding areas during the winter.  If sensible hygiene precautions are observed you can continue to enjoy feeding birds in your garden and watching them nest and raise their young.  Once birds have started nesting you should not attempt to scare them away or damage the nest.

 

Information on handling of dead birds and the circumstances in which you should report them is provided on the Defra website, slong with contact details.

 

The avian influenza pages on the Defra website provide a comprehensive resource on the disease, with links to other key information sources.  There is also a Q&A page that provides answers to many more questions not covered in this note, especially where these relate to the poultry industry, cage birds and racing pigeons, or human health.