Risk of misinformation and adverse policies

The spread of HPAI H5N1 is of public concern, and receives a lot of attention in the media. Yet there remains widespread misunderstanding of the issue, especially about the different ways in which the virus might be spread. Misinformation has led to wild birds being automatically blamed. This creates political pressure for ill-advised and disproportionate policies such as the culling or harassment of wild birds and the destruction of wetland habitats. Other modes of transmission, such as the trade in poultry and poultry products, the trade in cage birds and human movements may well play a far more significant role in the spread of HPAI H5N1. In some cases, these modes of transmission have been underestimated and do not receive proportionate exposure in the media. We need to present an accurate and balanced view which acknowledges that there are a number of factors whose relative importance can change, depending on the area or outbreak concerned.

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What are the known causes of the spread of avian influenza?

The HPAI virus subtype H5N1 infecting poultry, other domestic animals, wildlife and humans almost certainly originated from the mutation of a low or non-pathogenic virus on poultry farms in East Asia. The virus then spread rapidly within and between farms, taking advantage of local practices in the feeding, housing, slaughtering and trade of domestic ducks, chickens and geese. Lack of hygiene, overstocking and mixing of different domestic animals greatly increases the risk of spreading the infection. Movements of people (e.g. farmers, veterinarians, and even journalists and tourists) and legal and illegal trade in caged birds are factors in the spread. As a result the virus may now be endemic in poultry of East and South-East Asia. Globalization has led to extensive and intensive movements of people, poultry and materials around the world at an unprecedented pace which provides greater opportunity for the spread of the virus. The outbreaks in Nigeria in early 2006, may have been caused by the supply of infected live poultry including day-old chicks from different sources, including East Asia and Turkey. Samplings of 5000 wild water birds in African wetlands support the view, since no evidence of HPAI H5N1 was found, that wild birds probably play a relatively minor role in the spread of avian influenza. This view is consistent with the fact that the northward migration of wild birds from Africa to Europe in the northern spring of 2006 did not cause any major outbreaks. Nor do wild birds seem to play a role in a country like Indonesia where HPAI H5N1 has been present for some years and where several human casualties have occurred. In February 2007 HPAI H5N1 was detected on a turkey farm in Suffolk, UK. It has been established that the strain of the virus found in the UK was similar to the H5N1 strain discovered on a poultry farm in Hungary, which pointed to a transmission route from poultry to poultry and not from wild birds to poultry. The outbreaks took place in a non-migratory period and at a site which was not adjacent to major wetlands, nor to areas used by significant numbers of waterbirds. So wild birds were unlikely to have played a significant role during these outbreaks. The outbreaks in Central Europe between June and August 2007, where a number of dead wild birds infected with H5N1 were consecutively found in different parts of the Czech Republic, Germany and France were most likely linked to a H5N1 outbreak in a Czech turkey farm. Again, wild birds were unlikely to be the main factor spreading the virus since the outbreaks were observed in mostly non-migrant species and during the non-migratory period.

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The role of wild birds

It is clear that trade in domestic poultry has been a crucial factor, even for the transmission of avian influenza over long distances and across continents. However, numerous species of wild birds, especially waterbirds, have been proven to be susceptible to infection by HPAI H5N1. Close contact between wild birds and poultry can lead to cross-infection, from poultry to wild birds and from wild birds to poultry. The loss of wetlands around the globe may force many wild birds onto alternative sites like farm ponds and paddy fields, bringing them into direct contact with chickens, ducks, geese, and other domestic fowl. Additionally, species that live in and around poultry farms and human habitations may serve as “bridge species” that could potentially transmit the virus between poultry and wild birds. Analysis or genetic sequences and other indirect evidence suggest that in at least some cases wild migratory birds are likely to have contributed to further spread. The actual importance of this mechanism, however, is unclear in the present state of knowledge. Poor planning in response to development pressures has led to the increasing loss or degradation of wild ecosystems which are the natural habitats for wild birds. The displaced wild birds increasingly seek to feed and live in areas populated by domestic poultry (and humans). This provides greater opportunities for the spread of H5N1 between wild and domestic birds, and thence to humans. This issue of “ecohealth” highlights the interplay between agriculture, animal (domestic and wildlife) health, human health, ecosystem health, and socio-cultural factors. However, it is unlikely that wild birds play a major role in spreading avian influenza. The total number of wild birds affected has so far been small and although billions of wild birds cross continents regularly during their migrations they do not seem to have a significant impact on spreading the virus on a large scale.

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What an Early Warning System for wild bird avian influenza should look like

The development of global early warning systems (EWS), which incorporate the results of national and international surveillance programmes, should be a high priority, and aim for the following attributes:

• Open and transparent participation of relevant parties;
• Targeted active and passive surveillance and other data-gathering;
• Web-based output allowing the rapid dissemination of open-access data and information deriving from surveillance systems;
• Integration of surveillance results with geographical and other data to facilitate integrated responses and risk management;
• Meta-data allowing full analysis and interpretation of results in order to facilitate appropriate responses (inter alia, information on type of surveillance (active or passive) and locations of sampling locations); and
• Facilitation of timely and effective risk management. This implies clear warning triggers and targeted reporting.

What science needs to explore further about the role of migratory waterbirds

We need improved international analysis of existing waterbird satellite telemetry, ringing (banding) and count data. This must synthesize information on the routes and timing of waterbird migration, especially of poorly known intra-African migrants, and birds using Central Asian, Asia-Pacific and Neotropical flyways. We need to strengthen bird research worldwide, especially in areas where little or no ringing and counting schemes have operated in the past. We need to publish the results of these studies and other relevant data in new flyway atlases available on the Internet. We need targeted international ringing, colour-marking and satellite telemetry programmes for waterbird species likely to be at higher risk of carrying HPAI H5N1. We need better and integrated data on trade in domestic poultry and other birds to build epidemiological models. We need to increase research on various aspects of the epidemiology and ecology of H5N1 in wild bird populations and in the environment.

These aspects include:

We need research on the behaviour and ecology of those migratory and non-migratory bird species living in close association with man, which might act as a 'bridge' for the transmission of HPAI between waterbirds and poultry. Such research should aim to develop practical guidance on ways and means of reducing this risk.

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Selected resources from external sites 

• UN Food and  Agriculture Organisation (FAO): Avian Influenza and Wild Birds
• Wetlands International: Avian Influenza and Waterbirds
• BirdLife International: Avian Influenza
• USGS National Wildlife Health Center (NWHC): Avian Influenza