Friday, October 02, 2015

H5N6: The Other HPAI H5 Threat


Recent H5N6 Activity – Credit OIE


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This time last year – a full month before we would see H5N8 suddenly appear in Western Europe (and later, North America), and two months before we were aware of a major outbreak of H5N1 in humans in Egypt – our bird flu focus was centered on a new, upstart virus called H5N6, which had first appeared in a Sichuan China poultry flock, killing one manin April of 2014.


Part of the `new wave’ of avian influenza  viruses – which began with the H7N9 virus in the spring of 2013 -  H5N6 was the second new HPAI H5 reassortant virus to show up during the first half of 2014.  


H5N8 had emerged in Korea three months earlier - but unlike H5N8 and its progeny (H5N2/H5N3) -  H5N6 immediately proved itself capable of infecting (and killing) humans.  The number of human cases reported remains low (n=4), but of those, three have died. 


The most recent case was reported in July (see WHO Update On H5N6 Case – China). 


Six months after H5N6  first appeared, we saw an FAO-EMPRES Report On The Emergence And Threat Of H5N6, with our first detailed look at the virus, along with a short list of other newly emerged HPAI H5 viruses (including H5N8 & H5N3), that presciently warned


At that point only Mainland China and Vietnam had reported the H5N6 virus, but there were concerns that it might follow in H5N1’s footsteps and begin spreading (via migratory birds) more extensively. 


Within weeks we would see a major spread of an emergent HPAI H5 virus, but it would turn out to be H5N8 instead.

While H5N8 (and its reassortants) made headlines invading European, Taiwanese, Japanese, and North American poultry, the H5N6 virus continued to show up sporadically in poultry flocks across China and Vietnam.   Last May it turned up in a Hong Kong Oriental Robin, likely brought in by a migratory bird.


Determining the full range and extent of H5N6 is difficult, due limited surveillance and the widespread use of HPAI H5 vaccines in both China and Vietnam. 


Poorly matched AI vaccines may suppress symptoms, but not necessarily prevent infection (see EID Journal dispatch Subclinical Highly Pathogenic Avian Influenza Virus Infection among Vaccinated Chickens, China) and may be at least partially responsible for the sudden proliferation of new avian flu subtypes we’ve seen emerge over the past couple of years (H5N3, H5N5, H5N6, H5N8, H7N9, H10N8, etc. ).


Although nowhere nearly as well studied as H5N1, H7N9, or H5N8, four months ago in H5N6 Rising: Infecting Birds, Humans, & Even Cats, we looked at a report which appeared last June’s Nature’s Scientific Reports, called Fatal H5N6 Avian Influenza Virus Infection in a Domestic Cat and Wild Birds in China that warned:


Here, we report the first cases of fatal H5N6 avian influenza virus (AIV) infection in a domestic cat and wild birds. These cases followed human H5N6 infections in China and preceded an H5N6 outbreak in chickens.

The extensive migration routes of wild birds may contribute to the geographic spread of H5N6 AIVs and pose a risk to humans and susceptible domesticated animals, and the H5N6 AIVs may spread from southern China to northern China by wild birds. Additional surveillance is required to better understand the threat of zoonotic transmission of AIVs.


While we wait and watch for the return of H5N8/H5N2 in North America, or the resumption of Egypt’s H5N1 epidemic, it is worth noting that there are a number of other HPAI viruses circulating in China and Southeast Asia, and like H5N1 and H5N8, they could someday turn up in Europe or North America. 


Just last June, in J. Virol: Emergence Of AN HPAI H5N9 Virus In China) we learned of yet another HPAI H5 reassortant.


This week, once again, we are seeing reports of HPAI H5N6 in Vietnam (see CIDRAP Report  H5N6 detected again in Vietnamese poultry), and with the fall migratory season about to begin, we’ll be watching for any signs of spread to neighboring countries.


While  it is impossible to predict what any of these individual HPAI subtypes do - or where they will eventually spread – the rapidly increasing diversity and spread of these viruses raises the stakes not only for the poultry industry, but potentially for public health as well.