As of August 24, the US Centers for Disease Control and Prevention (CDC) reported 276 confirmed human cases of influenza A (H3N2) variant virus (H3N2v) in 10 states: Hawaii (one), Illinois (four), Indiana (138), Maryland (12), Michigan (five), Minnesota (one), Ohio (98), Pennsylvania (six), West Virginia (three), and Wisconsin (eight). This H3N2v virus has acquired the M gene from the 2009 H1N1 pandemic virus, which may make the H3N2 viruses more readily transmissible from swine to humans.
Most cases occurred in children involved in swine exhibitions at state and county fairs. The patients exhibited typical influenza-like symptoms, including fever, cough, runny nose, sore throat, and muscle aches. Although most human illnesses have followed either direct or indirect exposure to swine, CDC reported three instances of suspected human-to-human transmission. The agency noted, however, that the H3N2v virus has not previously spread easily from person to person. Interestingly, at the time of this writing, there have been no reports of disease in swine veterinarians or producers associated with commercial swine production.
This experience highlights the importance of United States Department of Agriculture’s (USDA’s) Swine Influenza Virus (SIV) Surveillance Program. This voluntary program was implemented to monitor influenza viruses in the US swine herd and provide viral isolates to animal-health and public-health officials for research and vaccine development. The overarching objective of the program is to better protect public and animal health. Analysis of test results can provide some insight into influenza virus activity in swine samples submitted to veterinary diagnostic laboratories.
The SIV Surveillance Program has provided us with some insight into the presence of this virus in the US swine herd. Since its inception in October 2010 through July 31, 2012, the surveillance program has tested 12,662 samples from 3766 swine diagnostic laboratory submissions. Over that time period, 1488 case submissions have been identified as positive for influenza A infection. Overall, 73 H3N2-positive submissions were detected in fiscal year (FY)2011 (October 1, 2010 to September 30, 2011) and 138 in FY2012 (October 1, 2011 to July 31, 2012). Of the 138 H3N2 cases identified in FY2012 tested to date, 57 contain the pandemic M gene and were classified as H3N2pM. Several additional H3N2-positive submissions remain under advanced diagnostic processes.
The information collected as part of the surveillance program is very important when we try to understand how these viruses are changing and moving within and between the swine and human populations. Monitoring influenza viruses can provide insight into potential impacts on swine health and possible transmission into the human population. While we have seen a good response following the implementation of the program, the greater the participation by swine veterinarians and producers, the more accurate and complete is our ability to prepare for and respond to changes in the influenza virus. Samples can be entered into the program anonymously, identifying only the state from which the sample was collected. Only aggregate results will be reported by USDA and in a manner that protects producer confidentiality.
In case you were wondering about the origin of the name “H3N2v,” it arose out of collaboration between CDC and a number of international groups, including the World Health Organization (WHO), the World Organization for Animal Health, the United Nations’ Food and Agriculture Organization, and others. To ensure accurate naming, the groups agreed to a standardized naming convention. Influenza viruses that normally circulate in pigs and may infect humans will be referred to as “variant influenza viruses,” designated by a “v.” “Variant” designates the virus as one that varies from infecting only the species that is its usual host. Centers for Disease Control and Prevention officials say that when influenza A (H3N2) viruses are found in swine, they should be called “swine influenza A (H3N2)” viruses. Another way of saying this is “swine H3N2.” If human infections with these viruses occur, these viruses are then called “variant” viruses as designated by the WHO, because they are infecting a different species, and are called “influenza A(H3N2)v” or just “H3N2v.”
So, as we enter the traditional height of swine influenza season, it’s time to once again raise our level of awareness about this virus and be on the lookout for potential changes in viral presentation and vaccine response. Be sure to remind the producers you work with about the importance of hand washing, vaccination, and keeping sick workers away from the pigs. Also, if you do not already participate, please consider participating in the SIV Surveillance Program. The information collected provides another piece of the puzzle that helps us protect swine and public health and promotes domestic and international markets for US pork products. Additional information is available from the AASV, the National Pork Board, and the CDC.