H3N2 influenza virions –CDC PHIL
# 6001
The CDC announced today the detection of two new novel flu isolates; one in West Virginia (trH3N2) and another in Minnesota (A/H1N2).
The West Virginia virus isolate is described today by the CDC as being:
A novel influenza A (H3N2) virus with genes from swine, human, and avian lineages with the M gene from the 2009 H1N1 virus that was first identified in August 2011. Ten prior human infections with this virus in four other states have been confirmed.
This virus is distantly related to an H3N2 virus that circulated 20+ years ago, which may explain why those born after 1990 have made up vast majority of cases detected so far.
Earlier posts on those cases include:
Branswell On The New trH3N2 Flu Virus
CIDRAP: New Details In The trH3N2 Story
ECDC Risk Assessment On trH3N2 Cases In North America
CDC Update On Iowa trH3N2 Cases
The Minnesota isolate is an H1N2 virus that has been known to circulate in swine for some time, and is said to be similar to an H1N1 virus (A/New Caledonia /20/99-like) that circulated as recently as 2007.
In neither case did these patients have recent known contact with swine, and so these reports imply that low level human-to-human transmission may have taken place.
First stop, a notice in today’s (otherwise quiet) FluView week 48 Report, followed by some choice excerpts from the latest Have You Heard? statement from the CDC.
http://www.cdc.gov/flu/weekly/
Novel Influenza A Viruses:
Two human infections with novel influenza A viruses were detected in children from two states (Minnesota and West Virginia). One patient was infected with a novel influenza A (H1N2) virus and one patient was infected with a novel influenza A (H3N2) virus. Both patients have recovered from their illnesses. While both viruses are known to circulate in U.S. swine, there was no close contact with pigs reported preceding illness onset in either case. Both states have been investigating case contacts and sources of exposure, however, no additional confirmed cases have been detected at this time. Additional information on these cases can be found in the CDC Have You Heard posting.
CDC is required to report all cases of human infection with novel influenza viruses – including swine influenza viruses -- to the World Health Organization (WHO) as part of the International Health Regulations (IHR). Domestically, CDC reports these cases in this report and on its website. Early identification and investigation of human infections with novel influenza A viruses is critical to evaluate the extent of the outbreak and possible human-to-human transmission. Additional information on influenza in pigs and swine-origin influenza infection in humans can be found at http://www.cdc.gov/flu/swineflu/.
Below are some excerpts from today’s announcement (bolding & reparagraphing mine). Follow the link to read it in its entirety.
CDC confirms two human infections with novel influenza viruses
December 9, 2011 -- CDC has confirmed two cases of human infection with two different novel influenza A viruses in different states. Both patients have fully recovered. While the viruses infecting both patients have been found in U.S. swine and some of the prior human infections with these viruses have been associated with direct or close swine contact, there are no reports of direct or close contact with swine prior to illness onset in either of these cases. Laboratory testing at CDC has confirmed that both novel viruses are susceptible to the antiviral medications oseltamivir (Tamiflu®) and zanamivir (Relenza®).
<SNIP Narrative on 2 New Cases>
Detection of Swine Influenza Infections in Humans
Human infections with novel influenza A viruses normally found in swine are rare events. Recently, however, the frequency of such detections has increased.
This could be occurring for a number of reasons, including one or more of the following factors:
First, laboratory methods for testing for these viruses in the United States were improved following the 2009 H1N1 pandemic. These improvements may be resulting in viruses being identified now that would have gone undetected previously.
Second, this could be due to increased surveillance in the United States for influenza at this time of year. CDC has requested that states analyze, and then send, their first influenza virus specimens of the season for seasonal influenza surveillance purposes. This practice, coupled with very low levels of seasonal flu activity at this time, could mean that sporadic novel influenza infections are more likely to be tested.
Third, it is possible that the increased frequency of detection of novel influenza viruses with swine origins identified by CDC represents a true increase in the number of such cases, possibly occurring from exposure to infected swine or through subsequent, limited human-to-human transmission.
While the CDC and public health officials are obviously taking these novel virus detections seriously, and are ramping up surveillance to track their spread, it is too soon to know whether any of these new flu strains will take hold in the human population.
As I wrote in Pseudo Pandemics And Viral Interlopers it is certainly possible for new strains of influenza to appear and circulate among humans, without sparking a pandemic.
Influenza is notoriously unpredictable.
For now, we are in a watchful waiting mode; looking for signs that one of these novel viruses is getting better adapted to human physiology.
In the meantime, maintaining good flu hygiene this winter (washing/sanitizing your hands, covering coughs & sneezes, staying home when sick), and getting your seasonal flu shot, remain the best strategies to avoid getting sick during this flu season.
