#3761
imported_Martin
Participant

Review appearing in ornithological journal Ibis, now online. Includes:

Quote:
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.

Recent expansion of highly pathogenic avian influenza H5N1: a critical review[/url] also in Ibis, a Viewpoint article by Professor Chris Feare, includes:

Quote:
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 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.