# 5794
With yesterday’s FAO announcement (see FAO Warns On Bird Flu), the H5N1 virus is suddenly back in the news cycle again.
Today, the Australian Life Scientist Magazine carries an interview with world renown, 1996 Nobel Prize winning scientist Professor Peter Doherty, who discusses the pandemic potential of this avian virus.
Although his comments range from research on GM (genetically modified) flu-resistant chickens to universal flu vaccines, the main thrust of the today’s article centers around the possibility that the H5N1 virus might one day swap genes (reassort) with the H1N1 virus and produce an easily transmitted, highly virulent flu strain.
First a link to the article, which is very much worth reading, then I’ll return with more.
Bird-swine flu hybrid could be a killer combo
The appearance of a new mutant of bird flu in Asia raises the concern that it might hybridise with swine flu creating a new pandemic threat.
- Tim Dean (Australian Life Scientist)
- 30 August, 2011 17:12
As we’ve discussed before, influenza viruses change, evolve, or mutate over time via two well established routes; Antigenic drift and Antigenic Shift.
Antigenic drift – the more common of the two - causes small, incremental changes in the virus over time. Drift is the standard evolutionary process by which influenza viruses mutate, and often come about due to replication errors that are common with single-strand RNA viruses.
Shift occurs when one virus swap out chunks of their genetic code with gene segments from another virus. This is known as reassortment. While far less common than drift, shift can produce abrupt, dramatic, and sometimes pandemic inducing changes to the virus.
This process has produced pandemic flu strains in the past, and while that obviously doesn’t happen often, virologists are quick to remind us:
Shift Happens.
While reassortment can occur in many species, pigs have long been believed to be an ideal `mixing vessel’ for influenza because they possess both avian-like (SAα2,3Gal) and human-like (SAα2,6Gal) receptor cells in their respiratory tract.
That makes pigs susceptible to human, swine, and avian strains of flu. And while it may not happen often, they are capable of being infected by more than one flu virus at a time.
This is basically how the 2009 H1N1 pandemic virus evolved, although it took multiple gene swaps over a decade or longer before it finally emerged into the human population.
We know that reassortments do happen, but only rarely do they result in a biologically fit virus capable of causing a pandemic.
Most hybrid viruses are evolutionary dead-ends, are unable to compete, and die out within the host.
But as global pig production grows – particularly in places where biosecurity and surveillance may be lax – it creates increasing opportunities for a new, biologically `fit’ virus to emerge.
Source: FAO
Lest anyone doubt the ability of pigs to contract the H5N1 virus, a little over a year ago (see EID Journal: Asymptomatic H5N1 In Pigs) we saw research out of Indonesia that showed 52 pigs in 4 provinces were found to be infected with H5N1 between 2005–2007.
While there is justifiable concern over a reassorted H5N1 virus, bird flu isn’t the only pandemic player down on the farm.
The H9 and H7 avian viruses, along with various strains of H3 and H1 influenza (and others) are all potential candidates for reassortment.
For more on the reassortment potential of avian, swine, and human flu viruses, you can’t do better than Helen Branswell’s excellent Scientific American article from last December called Flu Factories, or her SciAm Podcast interview.
And for good measure, a sampling of a few of my earlier blogs on reassortment:
Review: Evolution & Adaptation Of The 2009 pdmH1N1 Virus
You Say You Want An Evolution?
EID Journal: Co-Infection By Influenza Strains
EID Journal: Swine Flu Reassortants In Pigs
If You’ve Seen One Triple Reassortant Swine Flu Virus . . .
