# 6015
We’ve two studies to look at today focusing on the trH3N2 swine flu viruses that have been making headlines for several months; one appearing in the Journal of Virology and the other in the journal Eurosurveillance.
First a recap of recent events.
Feel free to skip ahead if you are already up to speed on the history of this virus.
Excluding the 2009 `swine flu pandemic virus’, there have been 31 `novel’ swine flu infections detected in humans the United States since 2005.
Most appear to have been dead-end transmissions, and have come about from direct contact with pigs. The CDC believes only a few may have involved limited human-to-human transmission.
Up until last year, the most common strain of S-OIV (Swine-origin influenza virus) found in humans was a trH1N1 strain, but in 2010 we began to see a shift towards trH3N2 viruses.
This year, a new reassortant of trH3N2 has appeared on the scene that has picked up a the Matrix (M) gene segment from the 2009 H1N1 virus.
Reassorted viruses can result when two different flu strains inhabit the same host (human or otherwise) at the same time. Under the right conditions, they can swap one or more gene segments and produce a hybrid virus.
Unlike most of the earlier novel swine flu infections, this strain has shown increased signs of low level human-to-human transmission. You’ll find some recent coverage of this emerging swine flu variant in the following blogs:
Branswell On The New trH3N2 Flu Virus
While only a small number of these reassorted trH3N2 viruses have been detected, the concern is, that over time it could get better at infecting humans and present a public health threat down the road.
All of which serves as prelude to today’s studies.
First stop, a brief news summary by CIDRAP of a Journal of Virology article on recent H3N2 detections in Chinese pigs.
Novel reassortant H3N2 flu found in Chinese pigs
Chinese researchers have isolated three novel H3N2 reassortant viruses from pigs in southern China that contain genetic material from a pH1N1 strain, similar to those associated with 11 recent infections in US patients, according to a report yesterday in the Journal of Virology.
<SNIP>
In spite of their separation geographically and chronologically, they are genetically very closely related, the authors write. "This provides direct evidence that the pdm/09-like internal gene complex has been successfully incorporated into a swine H3N2 virus, and been prevalent in the pig population for a period of time," they add.
Dec 14 J Virol abstract
Most notable in this summary is that detections of novel trH3N2 viruses in Chinese pigs with the M gene from the pdmH1N1 strain go back well over a year.
Next stop, a report in Eurosurveillance that takes a detailed look at the genetic sequences, and evolution of this emerging trH3N2 virus.
Eurosurveillance, Volume 16, Issue 50, 15 December 2011
by B Lina, M Bouscambert, V Enouf, D Rousset, M Valette, S van der Werf
The authors conducted an analysis of hemagglutinin sequences (HA) from both human and swine-origin influenza A(H3N2) isolates and concluded that this new trH3N2 virus is most closely related (5.5% divergence) to the A/Wuhan/359/95 H3N2 strain that circulated in humans until the mid-1990s.
This strain was also incorporated into the seasonal flu shot as late as the 1997-98 northern hemisphere flu season.
Based on this study, they suggest that some degree of cross-protection is likely, particularly to those born before 1995.
They warn, however:
. . . it is impossible to predict if pre-existing immunity will be efficient against this virus, even if it seems likely that some cross-protection will exist; seroepidemiological surveys should be carried out to support or disprove this hypothesis.
The authors also express concerns over our current lab test’s ability to detect and identify these novel strains, stating that:
. . . specific RT-PCR methods should be developed, or alternatively, predefined algorithms with already existing discriminating molecular tools need to be implemented.
Whether any of these novel swine viruses manages to adapt well enough to humans to pose a significant public health threat is something we will have to wait to see.
But even if these novel viruses fail to thrive - and end up as little more than a footnote in the history of influenza - they provide a stark reminder that influenza viruses are constantly evolving and mutating, looking for an evolutionary advantage.
We watch these novel viruses closely because history has shown that . . . given enough time.
They tend to find it.
