Sunday, February 08, 2015

H5N1 Detected In B.C. Backyard Flock

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# 9686

On January 15th of this year we learned of the first detection of a reassorted HPAI EA/AM H5N1 virus in North America, when this emerging subtype was detected in a green-winged teal in Whatcom County, Washington (see OIE: New Reassortant HPAI H5N1 In North America).

 

While carrying the same HA/NA designations as its more infamous Asian cousin -  this subtype is comprised of gene segments from the Eurasian (EA) H5N8 virus, along with genetic contributions from North American (AM) avian viruses. 

In other words, a new version of H5N1.

 

The OIE described it as:

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.

 

Although this reassortant was discovered in only one bird last month, the implications are that it is probably spreading in other wild and migratory  birds as well, and so it isn’t terribly surprising that it would turn up again in the Pacific Northwest.

 

After a couple of days of rumors and  media reports, yesterday Canada’s CFIA posted the following  notice of the detection of this new virus in a “non-commercial’ flock in Chilliwack, BC.

 

CFIA confirms presence of H5N1 virus in British Columbia and removal of quarantines from three farms

February 7, 2015

The Canadian Food Inspection Agency (CFIA) is continuing its investigation into an outbreak of avian influenza in British Columbia's Fraser Valley. The CFIA has confirmed the presence of a high pathogenic H5N1 avian influenza virus on a non-commercial farm in Chilliwack, BC. The infected premises is under quarantine, depopulation of the affected birds has been completed and disposal measures are underway.

This is the first time the H5N1 strain of the virus has been detected during the current avian influenza outbreak in British Columbia's Fraser Valley. The other affected farms in BC were infected by the H5N2 strain.

The H5N1 strain was found in wild birds in Washington State in January 2015.

(Continue . . .)

 

This notification provides us with very little actual information beyond the requisite assurances that `Avian influenza viruses do not pose risks to food safety when poultry and poultry products are properly handled and cooked.’  

 

We are even left to assume that this H5N1 virus is a match for the Washington state finding (likely so, but not stated implicitly).

While some of their official nonchalance may be forced, it is absolutely true that so far we’ve not seen any evidence that reassorted HPAI H5 viruses descended from the recently emerged Eurasian H5N8 subtype (H5 clade 2.3.4.4) have the ability to infect humans. 

These are, however, early days. 

And as new reassortants appear, and evolve, their behaviors and properties can sometimes change. Something our own CDC took notice of a little over a week ago, when they published interim guidance (see here and here) on testing and managing individuals potentially exposed to novel (H5 or H7) avian flu.  They wrote:

The appearance of newly detected avian influenza A H5 viruses in North America may increase the likelihood of human infection with these viruses in the United States. Because these newly identified avian influenza A H5 viruses are related to avian influenza A viruses associated with severe disease in humans (e.g., highly pathogenic Asian-lineage avian influenza A (H5N1) virus), they should be regarded as having the potential to cause severe disease in humans until shown otherwise

 

Of course, it is perfectly possible that H5N8 derived viruses – like the H5N2 viruses we’ve seen in the past – pose very little threat to human health.  But to assume such based on a very a limited track record would be folly.   The reason that H5 and H7 avian viruses are reportable to the OIE is because of their track record of quickly changing as they passage through birds.


For now, however, the big risk is to poultry operations. 

 

Unlike in Asia and the Middle East, which have endured heavy avian flu losses for more than a decade, North American poultry producers have not had to deal with these highly pathogenic H5 viruses.  If one or more of these subtypes (or future reassortants from them) manages to become endemic in North American birds - and that may already be happening -  the risks to the industry will only escalate.

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