Wednesday, February 01, 2017

H5Nx: Why North America Must Remain Alert


While North America has gone unscathed in this winter's unprecedented spread of, and outbreaks from - HPAI H5N8, H5N6, and (now) H5Nx  across Europe, the Middle East, Africa, and Asia - there are no guarantees how long our luck will hold. 
HPAI H5N8 appeared two years ago - presumably brought in by migratory birds from Asia - and caused the biggest avian epizootic in American history, affecting 15 states and causing the loss of nearly 50 million birds.
Why it hasn't returned (or been joined by H5N6, now circulating in Korea and Japan) is a matter of conjecture, but today there's not doubt that it could happen again.  Perhaps even more worrisome is this winter's persistence, and spread of HPAI H5Nx viruses (H5N8, H5N2, H5N5, etc) in Europe, given our shared migratory flyways (see map above).

First, a recent report from a Professor at Cornell University's College of Veterinary Medicine - Dr. Colin Parrish - then I'll return with some earlier studies on the North Atlantic Flyway's potential for introducing avian flu viruses from Europe

This from Cornell University.

Migrating birds may bring bird flu to North America

Colin Parrish, John M. Olin Professor of Virology at the Baker Institute for Animal Health in Cornell University’s College of Veterinary Medicine, an expert on influenza viruses and the spread of the virus in animals, says the highly pathogenic influenza strain currently infecting wild birds and domestic poultry in several European countries could be transmitted to birds in North America as migratory flyways of some European and North American wild bird species overlap in the northern reaches of Canada.


Parrish says:

“The strain circulating among birds in Europe is known as the H5N8 subtype, and this particular virus is a highly pathogenic influenza strain that appears to be readily transferred into poultry flocks and other domesticated birds from wild birds.

“Migratory birds in Europe and in America normally follow separate north-south migratory pathways, and there is normally not much mixing between birds in each region, but there are areas where they come in contact. This virus seems to be quite transmissible, so there’s a reasonable possibility that it could be picked up and brought over to the North American flyways. It looks like H5N8 is very effective at transferring from the wild birds into domestic poultry operations, so this is a concern.

“As we can’t do anything about bird migration, we have to be really vigilant about the possibility so we can control H5N8 in domestic birds if it arrives. The virus appears to cause severe disease in most birds that it infects, so it is likely that state surveillance would detect it pretty quickly if it were to arrive in North America.

“Influenza is a virus that emerges periodically to cause epidemics in different birds or mammals, like the two types of canine flu we now have in North America and the recent feline influenza outbreak in New York City. We need to stay on top of it. We can’t let down our guard.”

The overlap between the East Asian and Pacific America flyway has always been viewed as the most direct route for birds to carry HPAI into North America - and made good on that potential with 2014's arrival of H5N8 - but three  years ago we looked at the potential of avian flu arriving via the transatlantic route (see PLoS One: North Atlantic Flyways Provide Opportunities For Spread Of Avian Influenza Viruses).
So while less obvious a threat, the North Atlantic Flyways are considered a potential air-bridge for the introduction of new (or components for a reassorted) virus to North America.

In 2014 the USGS reported:
The North Atlantic region is a newly discovered important pathway for avian influenza to move between Europe and North America, according to a U.S. Geological Survey report published today.
USGS scientists and Icelandic partners found avian flu viruses from North America and Europe in migratory birds in Iceland, demonstrating that the North Atlantic is as significant as the North Pacific in being a melting pot for birds and avian flu. A great number of wild birds from Europe and North America congregate and mix in Iceland's wetlands during migration, where infected birds could transmit avian flu viruses to healthy birds from either location.

By crossing the Atlantic Ocean this way, avian flu viruses from Europe could eventually be transported to the United States. This commingling could also lead to the evolution of new influenza viruses. These findings are critical for proper surveillance and monitoring of flu viruses, including the H5N1 avian influenza that can infect humans.

Up until very recently the evidence suggested that HPAI viruses only circulated in migratory waterfowl for a limited period of time, killing off a small number that were susceptible, while the rest used their preexisting immunity to LPAI viruses to fend off the threat.  
Following our North American epizootic over the winter of 2014-15, HPAI H5 viruses all but disappeared in the wild (see PNAS: The Enigma Of Disappearing HPAI H5 In North American Migratory Waterfowl).

In a similar vein, last September, in Eurosurveillance: Lack Of Evidence For Continued Circulation Of HPAI H5N8 In The Netherlands, a European study found little or no evidence of active H5N8 infection in any of the birds sampled since their 2015 outbreak ended.
But since early fall we've seen a decidedly different pattern emerge with HPAI H5 viruses in both Europe and Asia.  Both H5N6 and H5N8 have produced far more more virulence in wild birds than we've ever seen before, and yet - despite large bird die offs - the virus appears to be spreading more efficiently via migratory birds than ever.

Last week, in a Risk Assessment On HPAI H5, Germany's FLI wrote: 
So far, the virus has been detected in 46 different bird species including species belonging to the categories diving ducks, grebes, sea gulls, swans, in isolated cases dabbling ducks (mallard duck), geese, birds of prey and also carrion-eating songbirds (e.g. crows). As at present mainly wild birds which have been found dead are investigated, it is unknown which other bird species may possibly carry the virus and do not develop symptoms of disease or die. It must be concluded that there is an ongoing HPAI H5N8 epidemics among wild water bird species and that the dead birds found possibly represent no more than the tip of the iceberg.
As HPAI H5 evolves, and its behavior changes, we seem to be trading one enigma for another.
A big test will come this summer and  fall, when we see if these new HPAI H5 viruses continue to circulate in the wild over the summer, of if they die out as we've seen them do in the past.  
Conventional wisdom says that the fall migration is far more likely to spread HPAI viruses than does the spring.  And so our luck may hold . . . at least in the short term.

But of late, when it comes to bird flu, conventional wisdom has been taking it on the chin.  And so now is definitely not the time for poultry producers to let down their guard - in North America - or anyplace else in the world.