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At the risk of piling on this morning, even as we track H7N9 and nCoV, it is worth recalling that last summer our attention was heavily focused on outbreaks of several variant swine flus, which infected hundreds of people who attended state and county fairs across the Midwest.
Asymptomatic Pigs: Revisited
MMWR: H3N2v Related Hospitalizations In Ohio – Summer 2012
The Return Of H1N1v
While we talk about the H3N2 virus as if it were a single entity – or at worst, a handful of strains - in truth there are more than a thousand variations of that virus, and most are currently only found in pigs and swine.
Descendents of the 1968 pandemic H3N2 virus continue to circulate outside of the human population, which has led researchers at MIT to consider its pandemic potential in a new study that appears today in Nature’s Scientific Reports.
Antigenically intact hemagglutinin in circulating avian and swine influenza viruses and potential for H3N2 pandemic
Kannan Tharakaraman, Rahul Raman, Nathan W. Stebbins, Karthik Viswanathan, Viswanathan Sasisekharan & Ram Sasisekharan
- Article number: 1822 doi:10.1038/srep01822
- Received 21 December 2012
- Accepted 23 April 2013
- Published 10 May 2013
The 2009 swine-origin H1N1 influenza, though antigenically novel to the population at the time, was antigenically similar to the 1918 H1N1 pandemic influenza, and consequently was considered to be “archived” in the swine species before reemerging in humans.
Given that the H3N2 is another subtype that currently circulates in the human population and is high on WHO pandemic preparedness list, we assessed the likelihood of reemergence of H3N2 from a non-human host.
Follow the link to read the entire (and highly technical) study.
But briefly, what these researchers found was a wealth of H3N2 strains circulating in pigs and birds that are antigenically different enough from the strains that have circulated in humans to have pandemic potential.
For more on this, in a less technical vein, we go to this MIT press release.
Potential flu pandemic lurks
MIT study identifies influenza viruses circulating in pigs and birds that could pose a risk to humans.
Anne Trafton, MIT News Office
May 10, 2013
In the summer of 1968, a new strain of influenza appeared in Hong Kong. This strain, known as H3N2, spread around the globe and eventually killed an estimated 1 million people.
A new study from MIT reveals that there are many strains of H3N2 circulating in birds and pigs that are genetically similar to the 1968 strain and have the potential to generate a pandemic if they leap to humans. The researchers, led by Ram Sasisekharan, the Alfred H. Caspary Professor of Biological Engineering at MIT, also found that current flu vaccines might not offer protection against these strains.
“There are indeed examples of H3N2 that we need to be concerned about,” says Sasisekharan, who is also a member of MIT’s Koch Institute for Integrative Cancer Research. “From a pandemic-preparedness point of view, we should potentially start including some of these H3 strains as part of influenza vaccines.”
The study, which appears in the May 10 issue of the journal Scientific Reports, also offers the World Health Organization and public-health agencies’ insight into viral strains that should raise red flags if detected.
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Genetic similarities
In the new study, the researchers compared the 1968 H3N2 strain and about 1,100 H3 strains now circulating in pigs and birds, focusing on the gene that codes for the viral hemagglutinin (HA) protein.
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Seeking viruses with an antigenic index of at least 49 percent and glycan-attachment patterns identical to those of the 1968 virus, the research team identified 581 H3 viruses isolated since 2000 that could potentially cause a pandemic. Of these, 549 came from birds and 32 from pigs.
Until a few years ago it was widely believed that a variant of a currently circulating flu strain – like H1N1 or H2N2 – would have a tough time sparking a pandemic as levels of community immunity would be too high.
The events of 2009 have shown that to be a false assumption.
At the time we were intently focused on the H5N1 avian flu, only to have an upstart H1N1 virus unexpectedly jump from swine to humans in North America, and spark the first pandemic in more than 40 years.
All of which should serve as a sober reminder that as we focus on the events in China and the Middle East, that nature can throw us a curveball from practically any direction.
