ECDC RAPID RISK ASSESSMENT FOR THE EU
It is important to emphasise that the viruses circulating in pigs in North America seem to be quite different from those reported in pigs in Europe. Swine influenza A(H3N2) viruses predominate in North America as triple reassortant viruses while the H3N2 viruses that are endemic in swine in some regions of Europe are antigenically and genetically different [6,7]. Reports of swine-origin viruses in humans in North America occur most years and since ‘novel influenza A viruses’ are a nationally notifiable disease in the US, laboratories that detect a possible novel influenza A virus are required to investigate the case and rapidly send laboratory specimens to the CDC for testing . By contrast, reports of swine viruses in humans in Europe are rare: there have been only two published reports since 2008 (one in Spain and one in Germany) plus the three cases from Switzerland that have yet to appear in the literature [14–16].
However, it must be noted that the discovery of the Spanish and German cases in humans was almost accidental, so it is likely that the numbers of human infections are underestimated. Following the emergence of the 2009 pandemic from pigs in Mexico there is a strong public health case for increased active ascertainment of human infections with swine viruses in Europe . Finally it should be noted that human influenza viruses from the 2009 pandemic may be circulating in pig herds in Europe, giving rise to the possibility of reassortment as demonstrated recently in Germany in which case these infections may not be detectable by conventional testing .
The risk of the emergence of a pandemic virus based on the American triple reassortant swine viruses with or without the A(H1N1) M gene cannot be known. This is only one of a number of potential pandemic influenza viruses. Others include A(H9), A(H2) and A(H5N1) viruses. An international initiative recently started with the aim of judging which candidate viruses are most likely to warrant the development of pandemic preparedness tool-kits that include both diagnostic components and early vaccine development . That initiative is not yet developed enough to justify its application to S-OtrH3N2 viruses but they would be early candidates for consideration. In Europe this initiative is being supported by the European Food safety Authority .
CONCLUSIONS AND RECOMMENDATIONS
The viruses in question have not been seen in pigs in Europe (EU/EEA) but there has been swine-to-human transmission in Europe with European viruses. However, there are no reports of anything but mild self-limiting illness and no ongoing transmission. The clinical picture is in stark contrast to avian influenza A(H5N1) infections .
Surveillance for infections in humans in contact with pigs is not as robust in Europe as in the US and there are strong public health reasons for strengthening surveillance of animal infections on both continents. Human influenza viruses from the A(H1N1) pandemic may be circulating in pigs and reassortant viruses from pigs have also been described recently. This is in addition to integrated virological, clinical and epidemiological surveillance of human infections in various healthcare settings (community, primary care, hospitals including intensive care units).
It is important to ensure that there is at least national capacity for detecting these viruses in EU/EEA countries and ECDC should work with the Community Network of Reference Laboratories (CNRL) to determine what methods are being used. Depending on the results of that exercise it may be worthwhile to issue guidance on recommended options for potential sampling and testing.
Another area requiring rapid work is determining what to call these and other new influenza viruses, since whilst a virological terminology such as S-OtrA(H3N2) plus an A(H1N1) M gene and A(H1N1)pdm09 may be essential for technical discussions, it does not facilitate communication.
It is impossible to comment on the pandemic potential of the current swine influenza viruses but formal virological risk assessments on the pandemic potential of emerging viruses like these are under development.
It is possible that these triple reassortant infections will appear in Europe, particularly if there is more human-to-human transmission, which could lead to imported cases. Hence Member States should continue to work with WHO and ECDC-CNRL to ensure there is diagnostic capacity at least at the national level in EU/EEA countries.
Finally, the situation highlights the importance of early and rapid referral of unusual influenza viruses, along with relevant clinical and epidemiological data, to National Influenza Centres and on to the WHO Collaborating Centre in Europe.
Relevant EU swine influenza websites:
ESNIP2 - European Surveillance Network for Influenza in Pigs 2: http://www.esnip.ugent.be/
ESNIP3 - European Surveillance Network for Influenza in Pigs 3: http://www.esnip3.eu/
FLUPIG - Pathogenesis and transmission of influenza in pigs: http://www.flupig.ugent.be/
RISK ASSESSMENT Swine-origin triple reassortant influenza A(H3N2) viruses in North America
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RISK ASSESSMENT Swine-origin triple reassortant influenza A(H3N2) viruses in North America
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