Late last October a newly reassorted, and far more virulent (in birds), HPAI H5N8 virus arrived in Europe and over the next several months sparked their largest avian epizootic on record. Aside from its pathogenicity, it also became known for its promiscuity, reassorting on several occasions with local LPAI viruses, and churning out new subtypes.
In mid-December of 2016, we learned of the emergence of a newly reassorted HPAI H5N5 subtype, isolated from a duck collected the previous month in the Netherlands (see OIE Notification), apparently a spin off from the newly arrived H5N8 virus.
Slowly at first, we began to receive other reports (from Italy & Montenegro) of this HPAI H5N5 virus detected in wild birds, but by late January the virus was discovered in a commercial flock for the first time (see HPAI H5N5 Detected In German Poultry Operation).
Germany's Friedrich-Loeffler-Institut (FLI) described this new virus as:
Since mid-December 2016 a further subtype, H5N5, has been circulating in wild birds, which now has first been introduced into a poultry holding. This virus is is likely to be a reassortant based on the original H5N8. Mixed viruses, so-called reassortants, of avian influenza viruses are generated, if several virus subtypes are present in one infected animal and exchange genetic material during replication. Generation of reassortants must be expected when different high and low pathogenic influenza viruses are circulating in one population.A relatively minor player compared to H5N8, this newly emerged H5N5 virus was described as `highly aggressive' by Germany authorities, and began turning up in other European countries as well (Slovenia, Greece, Poland, The Czech Republic, Macedonia, etc.).
After a horrendous winter, avian flu reports have declined sharply across western Europe, prompting most countries to sound the `all clear' last in April, once again allowing poultry to leave the barn.
What few reports we've seen over the past 60 days have been almost exclusively H5N8.But today we see a break in that pattern, one that reminds us that avian flu viruses - while greatly reduced - continue to circulate in the environment, with word from the government of the Netherlands that they've discovered two dead geese infected with H5N5 in the city of Utrecht.
In the city of Utrecht has been found in two dead wild geese bird flu of the highly pathogenic H5N5 type. Possibly this flu variant derived from a combination of the Influenza A virus subtype H5N8-type virus (which circulated in recent months in Europe) with another low pathogenic type. The H5N5 variant is recently more often found in wild birds.
The risk of contagion has lately decreased such that by April 19th. Were withdrawn almost all national measures. Although the risk has decreased, the virus is not completely gone. There are therefore still infected wild birds were found. Alertness in poultry remains offered. For example, good hygiene at the company still important.
This discovery does suggest that the H5N5 virus hasn't simply died out, and that it is still be circulating in wild birds (along with H5N8 and other AI subtypes), possibly even among wild birds in their summer roosting grounds in Russia and the Arctic.After its big debut in 2014-2015, HPAI H5 was unexpectedly a no-show during the winter of 2015-16 in Europe and the United States, and while it invaded Europe this past winter, once again it did not appear in North America.
So trying to guess exactly what it will do next fall, and where, is probably a fool's errand.But the general trend with HPAI H5 viruses (including H5N8, H5N6, H5N5, and H5N1) since late 2013 has been one of rapid geographic expansion, and increased virulence in birds. Add in the wild card of a new HPAI H7N9 virus in China, and we should probably enjoy whatever lull in bird flu activity that this summer brings.
And hopefully use that time wisely, to improve farm biosecurity, and to bolster our public health agencies and organizations to deal with whatever comes down the pike.