Since the emergence of A/H5N1 in the winter of 2005-2006 at the border of the European Union (EU), including human cases in Turkey, the European Centre for Disease Prevention and Control (ECDC) has developed assessments on the public health risks from A/H5N1, and guidance on how to protect those that may be exposed to the virus [1].

Over the last three years, the EU has also made strenuous efforts to improve the protection of EU domestic poultry from A/H5N1 infection, including enhancing biosecurity around domestic flocks and increasing veterinary surveillance activities in bird populations (wild and domestic) in order to provide an essential early warning of the presence of the virus (see Table).

Direct comparison of surveillance activity between the two periods is difficult, but the data available to date suggest a lower surveillance activity in wild birds in 2007 compared to 2006. There also remains large heterogeneity in the number of wild birds tested in all the Member States. However, the reported incidence data in 2007 are consistent with a relatively low level of A/H5N1 virus circulation within EU bird populations: infected wild birds have only been identified in four EU Member States, all within a short time-frame and a limited geographical area in central Europe (see Box).

As of 5 December, 307 wild birds have tested positive in the EU during 2007. The vast majority were found in Germany (298), with small numbers in France (7) the Czech Republic (1) and Hungary (1). Almost all these cases were reported in a seven-week period between mid-June and beginning of August [6]. This is in contrast to 2006, when 14 Member States reported a total of 748 positive cases of A/H5N1 in wild birds between February and August, indicating a broader distribution of the virus in the EU, mostly in a wave that rose and fell in the first half of the year [7].

The apparent lower level of virus circulation in wild birds during 2007 has not been reflected in the reported number of domestic poultry outbreaks in the EU. As of 3 December 2007, 14 outbreaks in domestic poultry have been reported in six Member States [8]. Although three countries (Hungary, Germany and the Czech Republic) have also reported cases in wild birds, the timing and location of cases in domestic poultry offer no obvious epidemiological link to wild bird infection in the majority of cases. This is in contrast to 2006, when most of the 33 domestic poultry outbreaks reported in the five affected Member States (Hungary (29), Sweden (1), German (1), Denmark (1) and France (1)) were preceded by the positive identification of virus in wild birds in the vicinity of the index case, giving a strong epidemiological link to the source of infection.

It seems, therefore, that unlike 2006, where proactive surveillance in wild birds established the presence of virus in several locations prior to the virus being identified in poultry, epidemiological data from 2007 did not detect infection in local wild birds before infection in domestic flocks. This is open to various interpretations, one being that EU wild bird surveillance, although extensive, has not been sufficient to trace infection in wild birds. However, in those areas where domestic flocks have been affected, even increased retroactive wild bird surveillance around cases in domestic poultry has, in most cases, failed to identify A/H5N1 infection in wild bird populations. This points to the possibility of other routes of entry into domestic poultry, such as through trade in poultry products, or via formites. The latter has been suggested in the linked outbreaks in Hungary and the United Kingdom (UK) in 2007 [9,10].

Conclusion
Irrespective of the cause, the infrequent but indiscriminate challenge from A/H5N1 may be the new reality that all owners of poultry in the EU, both commercial and hobby flocks, must now adapt to, at least in the short term. This also has important implications for public health: the apparently increasingly sporadic outbreaks of infection in domestic poultry, although uncommon, highlight the need for all owners of poultry to remain vigilant for the presence of infection in flocks. ECDC’s risk assessment is that those most at risk are people with small domestic and hobby flocks, rather than those working on large ‘industrial’ farms [11], although it is important that the prevention messages reach both. The truth of this was shown earlier this year, when an outbreak with another less pathogenic avian influenza infection (avian influenza A/H7N2) in poultry infected some owners, put a few people into hospital with illness and required many more to take prophylaxis [12].

Although there have been no human H5N1 cases in the EU, there is more than a theoretical possibility that cases will be seen in the future and that they will come from people with small backyards or hobby flocks. In order to minimise this risk, it is important to encourage good hygiene practises in all who have contact with poultry, including in particular avoiding handling sick or dead birds and regular hand-washing following any contact with birds. This is especially the case given the apparent uncoupling between cases detected in wild birds and domestic poultry; wild bird sentinels may not highlight the presence of infection before it appears in domestic flocks. Of course, there are a number of other zoonoses that are considerably more likely to be transferred from birds to their owners in the EU, but the same precautions recommended to protect against A/H5N1 will also protect against the other infections [13].

Overall, although the epidemiological interaction of H5N1 virus between wild birds and domestic poultry may have changed somewhat during 2007 in comparison to previous years, there is nothing in the international data to suggest that the virus has altered its characteristics in such a way as to increase the likelihood of transmission to humans. The ECDC has therefore not altered its standing risk assessment on the direct human health implications of the A/H5N1 viruses, which is that they are, at present, a group of influenza viruses of birds, poorly adapted to humans, whom they find hard to infect except at high doses. They are dangerous as they are highly pathogenic in those few humans that do become infected, but then they generally do not transmit on to other humans [14].