I don't believe wild birds are spreading h5n1

The reason I speculated that humans moving birds should
not be eliminated as suspects in the spread of this disease is that in my
experience sick and dead ducks don't fly far. But, people can very easily
move sick birds over many miles. The movements may be legal or illegal but
in an outbreak of disease, they usually happen. I don't think migratory
birds can be eliminated as major spreaders but you can never underestimate
the ability of humans to move disease.

The claim that migratory birds are responsible for the long-distance spread of highly pathogenic avian influenza viruses of subtype H5N1 rests on the assumption that infected wild birds can remain asymptomatic and migrate long distances unhampered. We critically assess this claim from the perspective of ecologic immunology, a research field that analyzes immune function in an ecologic, physiologic, and evolutionary context. Long-distance migration is one of the most demanding activities in the animal world. We show that several studies demonstrate that such prolonged, intense exercise leads to immunosuppression and that migratory performance is negatively affected by infections. These findings make it unlikely that wild birds can spread the virus along established long-distance migration pathways. However, infected, symptomatic wild birds may act as vectors over shorter distances, as appears to have occurred in Europe in early 2006.

Migratory birds are already affected by habitat destruction and climate change; alarmist statements blaming migrants for the spread of an emerging disease with pandemic potential and ignoring or underplaying the role of the poultry industry do not do justice to the complexity of the issues involved

The phenology and geographical pattern of expansion of the HPAI H5N1 does not correspond to the pattern of bird migration. First, it took several months for the virus to spread from China to the Balkans. Migratory birds such as ducks and waders travel several hundred kilometres in a single day. If migrating birds mainly dispersed the virus, the virus should also spread by large jumps of thousands of kilometres, throughout the migratory stopping places of Asia and Africa. The observed expansion has rather been by a progressive expansion from isolated outbreaks, the geographical pattern of which corresponds well with major routes and patterns of human commerce. Secondly, from July 2005 onwards, if migratory birds were a main agent of dispersal, one would have expected massive mortalities of wild birds, both in the breeding areas and along all migratory routes, as bird populations would have been encountering this virus for the first time. However, only sporadic cases were observed. The cases in Western Europe after the cold spell on the Black Sea showed that the virus can spread through infected wild birds travelling short distances (Feare 2007), but no evidence for long-distance transmission during seasonal migration has yet been found (Feare 2007). Analysing 52 introduction events into countries, Kilpatrick et al. (2006) concluded that both poultry and the trade in wild birds represent a larger risk than migratory birds for the introduction of HPAI H5N1 to the Americas.

In summary, although it remains possible that a migratory bird can spread the virus HPAI H5N1 and contaminate poultry, the evidence overwhelmingly supports the hypothesis that human movements of domestic poultry have been the main agent of global dispersal of the virus to date. The occurrence of an outbreak at a commercial turkey farm in Suffolk, England, in February 2007 fits this wider pattern.

In spite of the absence of evidence that migratory birds play a major role in the dispersal of the virus, many statements to this effect were made by international institutions, non-governmental organizations and media, and a debate between epidemiologists and ecologists followed (e.g. Normile 2005, 2006a, 2006b, Fergus et al. 2006). However, from autumn 2005 it was largely presented as fact that migratory birds were the main potential agent of global dispersal (e.g. Derenne & Bricaire 2005, FAO 2005), even as evidence emerged in Asia that spread was mainly mediated by human activities (Melville & Shortridge 2004). OIE reports (e.g. OIE 2005, 2006a, 2006c) indicated that the source of outbreaks was contact with migratory birds, but offered no evidence to support this assertion and contributed to the inappropriate emphasis on migratory birds, thus reducing the probability that alternative mechanisms such as poultry movements were fully considered in individual cases. In spite of the declarations of the Nigerian Minister of Agriculture on the probability of the introduction of the virus via the poultry trade (Euro Surveillance 2006), the FAO continued to implicate migratory birds, thus denying problems associated with commercial exchanges. The natural globalization of the exchanges of migratory birds seemed to hide the globalization – without strict health control – of the exchanges of poultry as the accepted mechanism for disease spread. By May 2006, an international conference in Rome had recognized that the virus was mainly spread through the poultry trade, both legal and illegal, but OIE and FAO media releases (FAO 2006b, OIE 2006b) continued to focus on the possible contribution of spread by wild birds. Given that a key part of the remit of the FAO is to develop international agricultural trade, reticence to accept that this trade is the main agent of global dispersal of HPAI H5N1 is perhaps unsurprising.

The most recent outbreak in western Europe, at a turkey farm in Suffolk, UK, is alluded to by Gauthier-Clerc et al. but evidence that has become available since their review was written illustrates many of the problems of H5N1 reporting. The outbreak was first blamed on wild birds, which veterinary investigators reported at the site and this received high press prominence. ... The 10 February 2007 issue of New Scientist magazine included a map of Suffolk showing the outbreak location and highlighting the proximity of the RSPB's Minsmere ‘wildfowl’ reserve. ... The preliminary Defra report on the outbreak (http://www.defra.gov.uk/animalh/diseases/notifiable/disease/ai/pdf/epide...) commented on site biosecurity including workers changing footwear on entering the turkey sheds. Biosecurity in parts of southeast Asia involves removing all clothing, walking through a hot shower, and then putting on a complete set of clean clothing inside the premises.

A surveillance study conducted over the past year by the Forestry
Ministry has found that migrating flocks of birds are not carrying
strains of avian influenza.

The H5N1 virus has so far only been found in either domesticated or
farming poultry, says the Forestry Ministry's conservation for
biological resources director, Adi Susmiyanto.

The ministry has been studying migratory and wild birds in locations
and clusters prone to bird flu in the hopes of identifying the
prevalence of the virus in the wild fowls.

Now, with the disease still centered in Asia and the failure of
migratory birds to spread the illness to Europe and North America,
the H5N1 virus has dropped out of the media spotlight. The dearth of
coverage has prompted some to think that the threat of a pandemic has
passed.

Health officials were surprised when flocks of migratory birds that
had flown south to Africa and then back to Europe last spring didn't
carry the H5N1 virus as expected. Neither did birds that wintered in
Asia and flew to Alaska last summer to breed. International bird
monitors also found no widespread deaths from the virus among
migratory birds.

Many experts now think that wild migratory birds are only bit players
in the spread of the disease. More likely culprits are humans who
clean, feed and house infected domestic birds and those who prepare
infected birds and transport them to commercial markets, said Rick
Kearney, wildlife program coordinator with the U.S. Geological
Survey.

"Migratory birds may contract the disease and continue in their
migration, but they clearly don't play a major or single role in
spreading the disease," Kearney said.

Highly pathogenic avian influenza (HPAI) H5N1 expanded considerably during 2005 and early 2006 in both avian host species and geographic distribution.

Domestic waterfowl and migratory birds are reservoirs, but lethality of this subtype appeared to initially limit migrant effectiveness as introductory hosts. This situation may have changed, as HPAI H5N1 has recently expanded across Eurasia and into Europe and Africa.

Birds could introduce HPAI H5N1 to the Western Hemisphere through migration, vagrancy, and importation by people. Vagrants and migratory birds are not likely interhemispheric introductory hosts; import of infected domestic or pet birds is more probable.

If reassortment or mutation were to produce a virus adapted for rapid transmission among humans, birds would be unlikely introductory hosts because of differences in viral transmission mechanisms among major host groups (i.e., gastrointestinal for birds, respiratory for humans). Another possible result of reassortment would be a less lethal form of avian influenza, more readily spread by birds.

Beyond the case Nigerian, the ornithologists point certain inconsistencies in the scenarios implying the wild birds. "There is no important migratory road of the east towards the west, and the exit of the virus of China towards Europe cannot be explained by migrating", known as thus the Richard Thomas, one of the persons in charge for Birdlife, an association of ornithologists based in London. "On the charts, adds Olivier Dehorter, specialist in the biology of the populations of birds to the national Natural history museum of natural history (MNHN), one distinguishes besides rather clearly that the infectious hearths follow the layout of the Trans-Siberian one."

In the same way, the researcher adds, who does not exclude a minor contribution from wild fauna to the propagation of the virus, "the second wave of contaminations which touched Turkey seems related to human activities - trade, displacements, etc. - that with movements of wild birds." In addition, known as Pascal Orabi, ornithologist with the League of protection of birds (LPO), "Australia and New Zealand, places of wintering of certain species which fly over Asia, remained unscathed".

A strong argument in favour of the implication of migrating remains the discovery in China, on the Lake Poyang (the World of February 8), of healthy wild ducks carrying the viruses, i.e. able to transfer it onto long distances. But wild fauna cannot be held for only culprit, according to Ward Hagemeijer, one of the persons in charge for Wetlands, the organization of study of the water birds based in the Netherlands, which undertook a study with the FAO and the international Center of research for agronomy and the development (Cirad). "We took nearly 7 000 wild birds in Africa, and no operational carrier of the virus was detected, specifies Mr. Hagemeijer. Even thing in the European Union, where 10 000 apparently healthy birds were tested, without positive result." The official results of these taking away, which continue, should be known in the next weeks.