Saturday, January 16, 2010

H3N2 Swine Flu




# 4260



Helen Branswell of the Canadian Press brings us details overnight of the detection of a single human infection by H3N2 swine influenza this fall in Iowa.   


While not believed to be terribly common, human infection by various (non pandemic) swine - and even avian - Influenza viruses probably happens more often than we think.


Improved surveillance and testing over the past couple of years will no doubt turn of more of these types of infections.


Farmers, hunters, and those who work closely with birds or swine are the most commonly affected.   Since most of these infections are mild, they often go unnoticed, or at least untested.


This story does have some unusual aspects to it.


First, the victim had no known contact with swine. This suggests a longer chain of infection, although there have been no signs of further human-to-human transmission.    Exactly how this person contracted the virus remains a mystery.


Second, this is a swine H3N2.   Up until a dozen years ago, only H1N1 was found in North American swine herds.


In 1998, a new triple reassortant H3N2 virus (with human, swine, and avian genes) was isolated, and has now become endemic in US herds. (see j virol. 2000 Sep, Evolution of swine H3N2 influenza viruses in the United States  and j virol. 2007, Interspecies and intraspecies transmission of triple reassortant H3N2 influenza A viruses ).


In 2006 and early 2007, an apparently reassorted H2N3 subtype was detected in pigs on two different Missouri farms, which was the first known appearance of an H2 virus in the wild since it was supplanted by the H3N2 virus in 1968.  


That discovery, along with the recent emergence of the novel H1N1 `swine’ flu last spring, gives further credence to the `pigs serving as influenza mixing vessels’ theory.



mixing vessel


All of which points out the importance of surveillance and testing of livestock in this country.


Helen Branswell bring us more details on this story.  Follow the link to read her story in its entirety.




U.S. CDC reports finding single case of a new swine flu; no sustained spread

By Helen Branswell Medical Reporter (CP)

TORONTO — Another new swine flu virus has made the leap to humans, though U.S. officials say it seems almost certain the virus hit a dead end.


The Centers for Disease Control reported Friday that a child from Iowa became infected with a new swine flu virus in September, though the case didn't come to light until November.


The unnamed boy didn't need to be hospitalized and recovered fully from the illness.


Testing later showed he'd been infected with a swine influenza virus of the H3N2 subtype, different both from the pandemic H1N1 virus and from the seasonal H3N2 viruses that have been circulating in people for decades.


Human cases of infection with swine influenza viruses happen from time to time. Often, though not always, these infections are seen in people who work on pig farms or in proximity to swine herds.

(Continue . . . )