Tuesday, August 21, 2012

Osterholm: Time To Close The Pig Barns


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# 6504


While the CDC has yet to find evidence of sustained and efficient human-to-human transmission of the emerging H3N2v flu virus, more than 200 human cases reported over the past couple of weeks have made it pretty apparent that this virus jumps readily from pigs to humans.


The CDC – citing the lack of H2H transmission and the relative mildness of infections – has advised county fairs and animal exhibits to screen pigs for signs of illness and urge better hygiene among visitors, but has stopped short of recommending the closing of pig barns to the public.


Complicating matters, last week we saw a study that showed pigs often carry flu viruses asymptomatically (see EID Journal: Flu In Healthy-Looking Pigs), which makes the advice to identify and isolate sick pigs problematic.


This morning, Helen Branswell has a long interview with well known flu expert and CIDRAP  director Michael Osterholm, who believes the time has come to close the pig exhibits at county fairs.


Osterholm stresses that we don’t yet know where this virus is going, or how much of a public threat it poses, but that the level of transmission at these venues is sufficient to warrant stronger measures.


A link to Helen’s article, then I’ll return with a postscript.


August 21, 2012 | 7:00 am

Time to close the pig barns, flu expert says

By Helen Branswell The Canadian Press

TORONTO – It’s been found in pigs and-or people in more than 10 U.S. states and counting. In less than a month, more than 200 people — most young children — have been infected by an unwanted visitor to many of the state and county fairs that are held at this time of year.


A new swine flu virus is infecting a growing number of people in the United States. But the official response to this outbreak is substantially different from the one that greeted the swine H1N1 virus that emerged in 2009.

(Continue . . .)



As I’ve pointed out before, every time this virus jumps from a pig to a human it gets another chance to better adapt to human physiology. Given enough chances, it could evolve into a greater public health threat.


So far, we’ve been lucky enough not to have seen a child’s death, or serious illness from this virus.


But when we do, you can be sure some aspects of the media a will have a field day excoriating the county fair, local officials, and health department that `let it happen’.


Admittedly, the suggestion to close the pig exhibits to the public will not be popular in the farm belt, or among pork producers (who have gone to great lengths to distance themselves from any connection to `swine flu’).


But whether the industry likes to admit it or not, pigs are highly susceptible to the influenza virus - and can even serve as `mixing vessels’ - allowing viruses to reassort into new hybrid strains.



Reassortant pig[6]


The pandemic virus that emerged in the spring of 2009 was the end product of several influenza strains that had kicked around the world’s swine population for many years, trading bits of genetic material back and forth, until they produced a version capable of jumping to humans.


The H3N2v virus is likewise a reassortant virus; swine H3N2 combined with the M (matrix) gene from the 2009 H1N1 virus. While the odds of seeing a pandemic emerge from this H3N2v virus appear low right now, they are not zero. 


Whatever negative publicity the pork industry might suffer from temporarily shuttering pig exhibits would pale in comparison to the backlash they would see should another swine-origin flu virus take off in a big way in the human population.


Nevertheless, the proposal to shutter pig barns is bound to be a sensitive one. It is going to be interesting to see how public health departments, fair officials, and the pork lobby react to Dr. Osterholm’s suggestion in the coming days. 


For more on the flu risks from swine reassortments, I’d heartily recommend Helen Branswell’s terrific piece in SciAm  from late 2010 called Flu Factories.

Flu Factories

The next pandemic virus may be circulating on U.S. pig farms, but health officials are struggling to see past the front gate

By Helen Branswell  | December 27, 2010 |



And for some of my earlier looks at swine influenza, you may wish to revisit:


H3N2v: When Pigs Flu

You Say You Want An Evolution?

The (Swine) Influenza Reassortment Puzzle

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