Swine-origin influenza viruses identified in humans will now be referred to as “variant” viruses and denoted with a “v,” according to the U.S. Centers for Disease Control and Prevention. The decision was made after discussions among the World Health Organization (WHO), the World Organization for Animal Health, the Food and Agriculture Organization, CDC, and other U.S. federal agencies.
An official from the National Pork Board expressed optimism for the new naming system. “We welcome the scientific view on naming these viruses,” said Paul Sundberg, DVM, vice president, science and technology, NPB. “This new nomenclature will make communications more accurate and help prevent unintended consequences of naming a virus based on just one part of its genetic makeup.” Sundberg said the new naming system will help avoid implicating any of the genetic contributors of recombinant influenza viruses.
This change in nomenclature follows an announcement by WHO of a decision to standardize nomenclature for the pandemic influenza A (H1N1) 2009 virus (which has had diverse names) as influenza A (H1N1)pdm09. Influenza viruses identified in swine populations will continue to be referred to as “swine influenza” viruses.
Human infections with the influenza viruses currently circulating among swine are rare, according to CDC. Since 2005, only 35 cases have been reported in the United States, but the frequency with which they have been detected increased in 2011.
Since August 2011, CDC has identified 12 human infections in five states with swine-origin influenza A (H3N2) viruses. Per the new naming convention, these H3N2 viruses will now be referred to as “influenza A (H3N2) variant viruses with genes from avian, swine and human viruses,” and will be abbreviated as “A(H3N2)v” for scientific use and “H3N2v” for general public use. These 12 A(H3N2)v viruses also have the M gene from the A(H1N1)pdm09 virus. Of the 12 cases, two were from Indiana, three from Iowa, two from Maine, three from Pennsylvania, and two from West Virginia.
To minimize the risk for interspecies influenza transmission, CDC and the Occupational Safety and Health Administration (OSHA) encourage swine workers to be vaccinated against human seasonal influenza, wear appropriate personal protective equipment, and practice good hygiene, such as washing hands thoroughly with soap and water, when in contact with swine, especially swine that show signs of illness.
The National Pork Board also recommends producers work with their veterinarian to develop appropriate prevention and control measures for influenza in swine, which can include vaccinating swine against swine influenza. Similar to humans, swine infected with influenza viruses do not always exhibit signs of infection. Persons with swine exposure in the week before onset of an illness with symptoms of influenza requiring medical care should notify their health-care provider of their swine exposures.
Persons who develop symptoms of influenza after close contact with swine are recommended to stay home until well to minimize contact with persons and swine as much as possible.
In July 2009, USDA’s Animal and Plant Health Inspection Service and the swine industry implemented a SIV surveillance program to characterize the distribution of SIV in U.S. swine herds. To date, approximately 150 SIV isolates have undergone sequencing of three genes (hemagglutinin, matrix, and neuraminidase gene segments).