H1N2 Variant Virus Detected in Minnesota

September 7, 2012 -- The Minnesota Department of Health has reported detection of 3 infections with an influenza A H1N2 variant (“H1N2v”) virus with the pandemic M gene from the 2009 H1N1 virus. These cases were reportedly associated with prolonged contact with pigs at a fair. H1N2 viruses normally circulate in pigs, not people, but rare human infections with this virus have been detected in the past. This virus is different from the H3N2v virus that, as of today, is reported to have caused 296 human infections across 10 U.S. states since July 2012. These additional human infections underscore the fact that swine influenza viruses can spread to people after close contact with infected pigs, and support the importance of ongoing surveillance for both human and swine influenza viruses.

According to the state of Minnesota, each of the 3 people infected with the H1N2v virus had exhibited pig(s) or spent prolonged time with pig(s) at the Minnesota State Fair. Two of the three people had underlying health conditions that placed them at high risk of serious flu complications; one of the two people with high risk factors was hospitalized, highlighting again the importance of the CDC recommendation that people with high risk factors avoid close contact with pigs and pig arenas at fairs this season. All 3 people have recovered from their illnesses.

People who are at high risk of serious flu complications include children younger than 5 years, people 65 years and older, pregnant women, and people with certain long-term health conditions (like asthma and other lung disease, diabetes, heart disease, weakened immune systems, and neurological or neurodevelopmental conditions). A full list of high risk factors is available on the CDC seasonal flu site.

In addition to avoiding pigs and pig arenas at fairs this year, as always, people with high risk conditions who develop flu-like symptoms should seek prompt medical attention. The H1N2v virus should be susceptible to both currently recommended influenza antiviral drugs [oseltamivir (Tamiflu®) and zanamivir (Relenza®)].

CDC has confirmed the Minnesota samples as H1N2v viruses. Sequencing of the viruses indicates these H1N2 variant viruses are very similar to those found in humans previously; with the exception of the addition of the pandemic M gene. This is the first time this virus has included the M gene from the 2009 H1N1 pandemic virus when isolated from a person. Genetic analysis shows that the hemagglutinin (H) of this virus is similar to human seasonal influenza viruses that circulated in people as recently as 2007, so there would likely be protective immunity against this particular virus in the human population.

The University of Minnesota Veterinary Diagnostic Lab also isolated an H1N2 virus from swine sampled at the Minnesota State Fair. Sequencing at National Veterinary Services Laboratories in Ames, Iowa, confirmed that it matches the human isolates from Minnesota. According to the USDA Swine Influenza Surveillance program, very similar H1N2 viruses – also containing the pandemic M gene – have been found in pigs since early 2010 in Minnesota and a number of other U.S. states.

For more information about swine influenza, see Information on Swine Influenza/Variant Influenza Viruses.

For more information about variant influenza virus infections, see Swine Flu (Variant Influenza Viruses) in Humans.

For more information about H3N2v, see Influenza A (H3N2) Variant Virus Outbreaks.

For information to the last time an H1N2v virus was detected in the United States, see Have You Heard: CDC confirms two human infections with novel influenza viruses.