# 5155
While influenza activity across most of the country is reported as low, with moderate activity reported primarily in the Southeastern states, there is some news in this week’s FluView report which is bound to get a lot of attention.
For the 6th time in two years, a novel H3N2 swine-type influenza has been detected in the United States.
As you may recall, just over a month ago we learned of two other novel H3N2 infections (see CDC: Statement On Swine H3N2 Influenza) in Wisconsin and Pennsylvania.
The CDC has issued a statement on this latest discovery, which I’ve linked to and excerpted below. But since this is a lengthy statement, I’ve pulled some bullet points out:
- Test samples from one patient in Minnesota were confirmed at CDC as positive for swine origin triple-reassortant (tr) H3N2 influenza viruses—viruses that normally infect pigs.
- Although human infection with swine influenza viruses is rare, it can occur.
- The patient in Minnesota with confirmed trH3N2 infection had exposure to pigs prior to illness onset.
- There is no documented human-to-human transmission of this virus or any evidence of community transmission at this time.
- An investigation of this case is ongoing.
- Cases of human infection with swine influenza viruses underscore the importance of ongoing human and animal influenza surveillance.
- The most recent Minnesota case brings the number of reports swine origin A (H3N2) infections in humans in the United States to six.
- Human infections with swine origin H3N2 virus infections have also been reported from Pennsylvania and Wisconsin in October and November 2010, Minnesota in May 2010, Iowa in September 2009, and Kansas in August 2009.
Follow the link to read this statement in its entirety.
December 17, 2010
Report of Human Infection with Swine Origin Influenza A (H3N2)
The December 17, 2010 FluView reported one human infection with swine origin influenza A (H3N2) virus in the state of Minnesota as part of U.S. surveillance and reporting of novel influenza A viruses. Test samples from one patient in Minnesota were confirmed at CDC as positive for swine origin triple-reassortant (tr) H3N2 influenza viruses—viruses that normally infect pigs. Although human infection with swine influenza viruses is rare, it can occur. This is most likely to occur when people are in close proximity to infected pigs, such as in pig barns and at livestock exhibits housing pigs at fairs. The patient in Minnesota with confirmed trH3N2 infection had exposure to pigs prior to illness onset. There is no documented human-to-human transmission of this virus or any evidence of community transmission at this time. An investigation of this case is ongoing. Cases of human infection with swine influenza viruses underscore the importance of ongoing human and animal influenza surveillance.
This case of human infection with swine origin influenza virus (SOIV) brings the total number of human infections with swine origin influenza viruses reported to CDC since 2005 to 19. Previously, five of these reports had been swine origin A (H3N2) viruses. The most recent Minnesota case brings the number of reports swine origin A (H3N2) infections in humans in the United States to six. Human infections with swine origin H3N2 virus infections have also been reported from Pennsylvania and Wisconsin in October and November 2010, Minnesota in May 2010, Iowa in September 2009, and Kansas in August 2009.
Swine influenza (swine flu) is a respiratory disease of pigs caused by type A influenza viruses that regularly cause outbreaks of influenza in pigs. Swine flu viruses can result in high illness rates in pig herds, but generally cause few deaths in pigs. Swine influenza viruses can circulate among pigs throughout the year, but most outbreaks occur during the late fall and winter months, similar to outbreaks in humans. There are four main influenza type A virus subtypes that have been isolated in pigs: H1N1, H1N2, H3N2 and H3N1. Most flu viruses circulating in pigs are referred to as "triple-reassortant" viruses because these flu viruses contain genes from human, swine and avian influenza viruses.
For more information about swine influenza, visit http://www.cdc.gov/flu/swineflu/
Weekly U.S. surveillance updates are published in FluView and posted at
While obviously of considerable interest (and perhaps, even a modicum of concern) I would remind my readers that only a tiny fraction of flu viruses are ever sequenced, and so we really don’t know how often these types of infections occur.
Probably more often than we think, would be my guess. And most apparently never go anywhere.
Otherwise we’d be be hip deep in novel H3N2 swine flu infections.
Swine have been long viewed as excellent `mixing vessels’ for influenza, but that process can take a long time before a `fit’ human adapted virus is produced. Novel H1N1 apparently bounced around in pigs for more than a decade before jumping to humans.
All of this highlights the need for upgraded, and continual surveillance of humans, and livestock, for emerging viral threats.
Because it isn’t if the next pandemic will emerge. It’s only a matter of when.
