Source EID Journal
# 6281
From the May edition of the CDC’s EID Journal we have a comprehensive look at the recently emergent H3N2v influenza virus has been detected in roughly a dozen patients across the United States since the middle of 2011.
Yesterday, in MMWR: Antibodies Cross-Reactive to Influenza A (H3N2) Variant Virus, we learned that while some adults have pre-existing cross-reactive antibodies to this virus - most children under the age of 10 do not – suggesting that young children are at the greatest risk of infection.
This finding is bolstered by initial reports showing that of the 13 known human infections, only one was reported in an adult.
While a lot of this report will be of greatest interest to researchers and virologists, I’ve excerpted a few pieces below. Follow the link to read it in its entirety.
Human Infections with Novel Reassortant Influenza A(H3N2)v Viruses, United States, 2011
Stephen Lindstrom, Rebecca Garten, Amanda Balish, Bo Shu, Shannon Emery, LaShondra Berman, Nathelia Barnes, Katrina Sleeman, Larisa Gubareva, Julie Villanueva, and Alexander Klimov
Abstract
During July–December 2011, a variant virus, influenza A(H3N2)v, caused 12 human cases of influenza. The virus contained genes originating from swine, avian, and human viruses, including the M gene from influenza A(H1N1)pdm09 virus. Influenza A(H3N2)v viruses were antigenically distinct from seasonal influenza viruses and similar to proposed vaccine virus A/Minnesota/11/2010.
Around the world, cases of human infection with swine-origin influenza viruses have been reported sporadically (1–5). From 1990 through 2010, a total of 27 cases of human infection with these viruses were confirmed by the US Centers for Disease Control and Prevention (CDC) (4,6). Of these cases, 21 were caused by triple-reassortant influenza A viruses (13 subtype H1N1, 1 subtype H1N2, and 7 subtype H3N2), which have inherited genes from classical swine, avian, and human influenza viruses. The 2009 influenza pandemic, caused by a variant triple reassortant influenza virus, influenza A(H1N1)pdm09 virus (7,8), proved that swine influenza viruses (SIVs) can cause widespread infection among humans and result in substantial economic costs. In 2010, an increase in the number of human cases of swine-origin influenza (H3N2) virus infection prompted selection of a candidate vaccine virus of swine origin, A/Minnesota/11/2010 (H3N2)v (9).
Systematic surveillance and characterization of novel viruses infecting humans and SIVs in swine are critical for early detection of viruses with pandemic potential. Since 2009, CDC has provided public health laboratories with a real-time reverse transcription PCR (rRT-PCR)–based assay for diagnostic testing for influenza (10). This assay enables detection and discrimination of influenza A virus subtypes H1N1, H3N2, and H1N1pdm09 and preliminary identification of triple-reassortant viruses possessing the nucleoprotein gene originating from SIVs.
< BIG SNIP>
Conclusions
The detection of multiple cases of human infection with influenza A(H3N2)v virus within a 5-month period in 5 US states, coupled with possible human-to-human transmission, underscores the need for continued influenza surveillance at the swine–human interface. Coordinated surveillance of human and animal influenza viruses enables rapid detection of human infections with novel influenza viruses and timely identification of new virus variants in swine. As was evident during the 2009 influenza pandemic, this information is vital for development of resources that might be needed to effectively respond to the emergence and spread of a novel influenza virus in humans.
Thirteen cases over 6 months (even assuming a substantial number of undetected cases) does not a pandemic make - and so far at least - we are not aware of this virus causing any serious illness or death.
But influenza viruses are moving targets, constantly changing and evolving, looking for an evolutionary advantage. What was true yesterday may not hold true tomorrow.
Over time this virus could become more transmissible, more virulent, or both.
Or it could it could end up in the evolutionary dustbin of failed organisms; little more than an interesting footnote in the history of influenza in the 21st century.
As with many other emerging viruses in the wild, we are in a watchful waiting mode. But whenever a virus jumps species, as this one has, we are particularly attentive.
In the meantime, the CDC is working on a vaccine should one be needed.
For more background on this H3N2v swine flu variant, you way wish to revisit some of these earlier blogs.
CDC/Medscape Video: Expert Guidance On The H3N2v Virus
WHO/FAO/OIE: Call It A(H3N2)v
WHO Comment: Testing For Novel Flu Viruses
Branswell On The New trH3N2 Flu Virus
CIDRAP: New Details In The trH3N2 Story
CDC Update On Iowa trH3N2 Cases
