Wednesday, January 21, 2015

OIE: New Reassortant HPAI H5N1 In North America



# 9608

Yes, you read the title right;  H5N1.  


Not the same H5N1 as has been rife in Asia for the past decade, and is currently making trouble in Egypt - but a cousin - a new reassortant H5N1 with genetic components derived from both the Eurasian H5N8 virus (including the H5 HA) and by North American avian viruses. 


A more complete description is provided in the OIE report below, after which I’ll be back with more.




Source of the outbreak(s) or origin of infection

  • Contact with wild species

As part of the increased AI surveillance of wild birds (performed by testing hunter harvested birds), another Eurasian H5 clade virus has been identified through whole genome sequencing of the virus isolate. Introduction of the Eurasian (EA) H5N8 virus into the Pacific Flyway sometime during late 2014 has allowed mixing with North American (AM) lineage viruses and generated new combinations with genes from both EA and AM origin (or “reassortant” viruses) such as the EA/AM H5N2-reassortant detected in Canada and the United States.

Such findings are not unexpected as the EA-H5N8 virus continues to circulate. A novel EA/AM H5N1-reassortant clade was isolated from an American green-winged teal in Whatcom County, Washington.

This H5N1 subtype is different from strain circulating in Asia. The gene constellation is as follows: Eurasian lineage genes (PB2, H5, NP, MP >99% identical to A/gyrfalcon/WA/41088/2014 H5N8); North American lineage genes (PB1 {98% identical to A/Northern pintail/Washington/40964/2014 H5N2}, PA, N1, NS of North American LPAI wild bird lineage. The HA cleavage site is compatible with strains that are highly pathogenic. This novel HPAI EA/AM H5N1-reassortant virus has NOT been found in commercial poultry anywhere in the United States.


H5N8 continues to impress in its ability not only to travel rapidly across continents and oceans on the wings of migratory birds, but in the number of viable reassortant viruses it has managed to  spawn along the way.  Last spring, in EID Journal: Describing 3 Distinct H5N8 Reassortants In Korea, we saw early indicators of this virus’s growing diversity, while just last week Taiwan reported two `new’ reassortant viruses (H5N2 & H5N3).


Right now we don’t know anything about how this new reassortant virus will behave in poultry (other than being HPAI), or in non-avian species (including humans).  I would posit that there is a good deal of testing & research going on right now to determine that. 

Whether this turns out to be a flash in the avian flu pan, or an early glimpse of a new emerging threat, this report does remind us that influenza viruses are capable of rapid evolution, particularly through reassortment.


The number of new avian viruses that have appeared over the past couple of years (H7N9, H5N8, H5N6, H5N5, H5N3, H5N2, H10N8, etc.) illustrate that nature’s laboratory is open 24/7, and one that can easily throw us a nasty curve ball at any time.

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