|H5N8 December 2014 - Credit DEFRA|
Although they were not hit nearly as hard as was North America, Western Europe saw multiple outbreaks and isolated detections of HPAI H5N8 during the fall-winter of 2014-15.
By the spring of 2015, however, reports in Europe ended.
Like in North America, the virus was fully expected to return in the fall of 2015, but did not. Since then, researchers have been trying to figure out why the virus seemingly vanished.
Yesterday the journal Eurosurveillance published a lengthy research article on virological and serological surveillance of wild birds in the Netherlands before, during, and after 2014's outbreak.
And, just as we've seen in North America, there's been little or no evidence of active H5N8 infection in any of the birds sampled since their outbreaks ended.
Last July, we looked at a similar study (see PNAS: The Enigma Of Disappearing HPAI H5 In North American Migratory Waterfowl)
which concluded while migratory waterfowl can briefly carry HPAI H5, they are not a good long-term reservoir for highly pathogenic avian flu viruses.
HPAI viruses appear to burn out fairly quickly in aquatic waterfowl populations, likely due to their immunity to LPAI viruses, and would have to be reintroduced periodically.
Another study, published last month in Sci Repts.: Southward Autumn Migration Of Waterfowl Facilitates Transmission Of HPAI H5N1, suggests that waterfowl pick up new HPAI viruses in the spring (likely from poultry or terrestrial birds) on their way north to their summer breeding spots.
The following fall enough of the virus may still be circulating among them - due in part to immunologically naive hatchlings born over the summer - to be spread during their southbound migration.
At least that's the theory.
Since HPAI H5N8 has recently been detected in both Alaskan and Russian wild birds, its possible we'll see that theory tested again this winter. Poultry producers in Europe, and in North America are being urged to beef up their biosecurity . . . just in case.
The abstract and some excerpts from yesterday's Eurosurveillance report follow.
Eurosurveillance, Volume 21, Issue 38, 22 September 2016
Lack of virological and serological evidence for continued circulation of highly pathogenic avian influenza H5N8 virus in wild birds in the Netherlands, 14 November 2014 to 31 January 2016
MJ Poen 1 2 , JH Verhagen 1 2 , RJ Manvell 3 , I Brown 3 , TM Bestebroer 1 , S van der Vliet 1 , O Vuong 1 , RD Scheuer 1 , HP van der Jeugd 4 5 , BA Nolet 4 6 , E Kleyheeg 4 5 , GJDM Müskens 7 , FA Majoor 8 , C Grund 9 , RAM Fouchier 1
Correspondence: Ron A M Fouchier (firstname.lastname@example.org)
Citation style for this article: Poen MJ, Verhagen JH, Manvell RJ, Brown I, Bestebroer TM, van der Vliet S, Vuong O, Scheuer RD, van der Jeugd HP, Nolet BA, Kleyheeg E, Müskens GJDM, Majoor FA, Grund C, Fouchier RAM. Lack of virological and serological evidence for continued circulation of highly pathogenic avian influenza H5N8 virus in wild birds in the Netherlands, 14 November 2014 to 31 January 2016. Euro Surveill. 2016;21(38):pii=30349. DOI: http://dx.doi.org/10.2807/1560-7917.ES.2016.21.38.30349
Received:05 April 2016; Accepted:21 July 2016
In 2014, H5N8 clade 18.104.22.168 highly pathogenic avian influenza (HPAI) viruses of the A/Goose/Guangdong/1/1996 lineage emerged in poultry and wild birds in Asia, Europe and North America. Here, wild birds were extensively investigated in the Netherlands for HPAI H5N8 virus (real-time polymerase chain reaction targeting the matrix and H5 gene) and antibody detection (haemagglutination inhibition and virus neutralisation assays) before, during and after the first virus detection in Europe in late 2014.
Between 21 February 2015 and 31 January 2016, 7,337 bird samples were tested for the virus. One HPAI H5N8 virus-infected Eurasian wigeon (Anas penelope) sampled on 25 February 2015 was detected. Serological assays were performed on 1,443 samples, including 149 collected between 2007 and 2013, 945 between 14 November 2014 and 13 May 2015, and 349 between 1 September and 31 December 2015.
Antibodies specific for HPAI H5 clade 22.214.171.124 were absent in wild bird sera obtained before 2014 and present in sera collected during and after the HPAI H5N8 emergence in Europe, with antibody incidence declining after the 2014/15 winter. Our results indicate that the HPAI H5N8 virus has not continued to circulate extensively in wild bird populations since the 2014/15 winter and that independent maintenance of the virus in these populations appears unlikely.
In conclusion, our results provide evidence that clinically unaffected long distance migratory and local wild birds sampled in the Netherlands during the H5N8 outbreak late 2014 and early 2015, and again late 2015, have been exposed to HPAI H5N8 or closely related HPAI H5 clade 126.96.36.199 viruses and seroconverted upon exposure.
Since HPAI H5N8 virus has not been detected in Europe since early 2015 and because HPAI H5 clade 188.8.131.52-specific antibody incidence decreased in time, we conclude that the virus has not circulated extensively at the breeding grounds in summer and upon the return of the birds to their wintering areas in the 2015/16 winter.
As a consequence, the newly emerging HPAI H5N8 clade 184.108.40.206 virus subtype appears to have already disappeared from European wild birds indicating that sustained transmission and independent maintenance may be less likely.
This is an important consideration in the ongoing evolution and ecology of these viruses in wild birds and the potential risks they pose for introduction to poultry and the pathways through which they might spread. Finally we recommend that serological tools be further optimised, harmonised, and validated for avian influenza surveillance studies in wild birds.