UK: DEFRA Cautions Pig Famers Over Avian Flu

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Overnight a number of UK farming publications have carried reports of warnings from DEFRA of the possibility that pigs in contact with infected birds could contract the H5N8 virus, and that if that happened, DEFRA could elect to cull them.

The following comes from the UK's National Pig Association website:

Pigs could be culled on farms affected with avian flu

7^th Feb 2017 / By Alistair Driver 

Producers have been warned pigs sharing premises where avian flu has been detected in poultry could be culled if they are found to be carrying the disease.

Pig farmers could also be required to undertake costly cleansing and disinfecting procedures, if avian flu is found on premises where both pigs and poultry are present.

The NPA has been seeking clarification from Defra about the situation for pig farmers, as the H5N8 strain of the disease has been confirmed at various poultry premises over the winter.

(Continue . . . )

Long time followers of novel flu are aware this is not a new concern, and that avian flu viruses have turned up in pigs before. In fact, the 2009 H1N1 pandemic virus the result of a triple-reassortment of swine, human, and avian flu viruses that had circulated for in pigs for years before jumping to humans.

Pigs are notoriously good hosts for influenza viruses, and due to having both mammalian α2,6 receptor cells and avian-like α2,6 receptor cells, are susceptible to a wide range of flu viruses.

While H1, H2, and H3 viruses predominate in swine (as they do in humans), we've seen more than a few examples of other subtypes infecting pigs.

• As early as 2004 the World Health Organization reported H5N1 in Chinese swine (see Avian influenza: H5N1 detected in pigs in China), sparking concerns over potential mammalian adaptation of the virus. 
• A 2008 study appearing in PLoS Pathogens found Domestic Pigs Have Low Susceptibility to H5N1 Highly Pathogenic Avian Influenza Viruses. While they could be experimentally infected, pigs demonstrated only mild disease, and did not shed the H5N1 virus as copiously as swine flu viruses.  
• More on point, however, is a study that appeared in the EID Journal in 2010 (Influenza A (H5N1) Viruses from Pigs, Indonesia), which found H5N1 infected pigs in 4 Indonesian provinces between 2005 and 2007, but not in 2008-2009.

The concerns over finding avian flu in pigs are actually two-fold.

The first is the potential for host adaptation of the virus. The serial passage of an avian virus from pig - to pig - to pig can, over time, allow genetic traits to emerge that make the virus more adapted to mammalian hosts (see Virology J : Adaptation Of HPAI H5N2 In Mice).

The second is viral reassortment, the creation of a novel hybrid virus cobbled together from gene segments from two or more parental viruses.

Granted, this doesn't happen often, and most of the time the result is an evolutionary failure, unable to compete with existing viruses.  But every once in awhile a new, `biologically fit' virus will emerge (see NIAID Video How Influenza Pandemics Occur).

Right now, with HPAI H5N8/H5Nx circulating in wild birds in Europe, concerns are naturally elevated, but avian viruses can make their way into pigs even when we are not on heightened alert.

Avian viruses (mostly LPAI, but sometimes HPAI) are nearly always present in migratory birds, and as 2009's pandemic taught us, their contributions to swine-origin viruses can lie dormant and go unnoticed for years.  

Add in the constant reintroduction of human influenza viruses, along with the existing (and continually evolving) hodgepodge of H1, H2, and H3 swine viruses, and you have a potentially potent brew.

In December of 2015, in PNAS: The Pandemic Potential Of Eurasian Avian-like H1N1 (EAH1N1) Swine Influenza, we looked at a study by Chinese and Japanese researchers who had isolated and characterized a number of avian-like H1N1 virus variants circulating in Chinese pigs that they believe have considerable pandemic potential.

They wrote:

Our study shows the potential of EAH1N1 SIVs to transmit efficiently in humans and suggests that immediate action is needed to prevent the efficient transmission of EAH1N1 SIVs to humans.

Last summer, in Sci Rpts: Transmission & Pathogenicity Of Novel Swine Flu Reassortant Viruses, we looked at another study - again out of China - where researchers experimentally infected pigs with one of these Eurasian-Avian H1N1 swine influenza viruses and the 2009 H1N1pdm virus.

In doing so, they generated yielded 55 novel reassortant viruses spread across 17 genotypes, demonstrating not only how readily EAH1N1 SIV can reassort with human H1N1pdm in a swine host, but also finding:

`Most of reassortant viruses were more pathogenic and contagious than the parental EA viruses in mice and guinea pigs'.

Whether pigs are susceptible to the HPAI H5Nx viruses currently circulating in Europe is still an open question.  In Korea, during their first year dealing with H5N8, they reported a number of dogs that had antibodies to the virus, so mammalian infection with this subtype is possible.

More recently, a study (see Sci Rpts: H5N8 - Rapid Acquisition of Virulence Markers After Serial Passage In Mice) suggested H5N8 could adapt to a mammalian host, and gain virulence, after only a few serial passages. 

While we are understandably on alert right now over avian flu in many parts of the world, we could very easily be blindsided by a swine-origin influenza virus instead. 

Or perhaps more properly, again.

All of which makes DEFRA's concerns, and advice to pig farmers, more than reasonable.