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Monday, 13 August 2012

An emerging outbreak of H3N2v swine influenza - what is the threat assessment?

The lay literature has touched on the threat of swine and the potential for influenza  Time August 10th.  In the background the machinations of the public health are starting to turn. With an epicentre in the Indiana –Ohio region of the US, some 153 cases have been identified in the past month compared with 13 in the previous year.   We have had enough false alerts that perhaps we should all be desensitized and just ignore the warning signs.

What makes this strain interesting, novel and perhaps disconcerting?  It is a swine based variant and normally not highly transmissible to humans, however this strain appears to have picked up the pandemic strain M gene which facilitates human transmission.

Admittedly that over half the cases appear to have been related to interactions with swine, and many to participation and attendance at farm fairs where pigs intermingle and humans enjoy their antics.  The other half likely represent first generation transmission between humans. Sustained human transmission has not yet been noted. 

The good news to date, is the severity of illness appears consistent with seasonal influenza, however the morbidity data to date are scarce.  The bad news is that current seasonal trivalent vaccines do not appear to confer much immunity (~15%). 

If you are looking for more information, follow the CDC Atlanta sites, there are multiple links that change frequently so take the time to check in regularly to find out what is changing CDC H3N2v information page .  Updated information tends to be posted as well to the MMWR MMWR home, and check in on ProMED where there are already 69 postings on this topic as of August 11.  ProMed home  

If one digs a bit deeper you will find that some of the current work has a Canadian flavour.  The influenza collaboration between BC including BCCDC, Quebec including INSPQ, and the National Microbiology Laboratory in Winnipeg is a tour de force of international experts and have already released several relevant papers on the H3N2v  J of Inf Diseases   Eurosurveillance

As with avian H5N1 that has been circulating since about 2000, and currently surging in Cambodia and Indonesia  WHO updates on H5N1, the US based H3N2v increase in activity is deserving of close observation.  H3N2v is not worth losing sleep over yet, but do expect more attention given it is just south of the border and has the expertise, resources and attention of the CDC.  It is also an excellent example of tracking and response to an emerging pathogen where little is known at the onset

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