Influenza concerns never really go away, rather they ebb and flow — and that doesn’t just apply to seasonality. Monitoring influenza in humans and animals is a full-time commitment.
It’s not yet three full years since the 2009 influenza A (H1N1) episode that developed into the first influenza pandemic since 1918, and wreaked havoc with U.S. hog prices and exports due to the questionable naming event. While you’re not likely to forget that debacle, the blow has softened a bit with time and pork exports’ record-setting recovery. That doesn’t mean you can relax your on-farm diligence.
In recent months, there have been a few cases of variant influenza viruses that included avian, swine and human genes (known as triple reassortant). Fortunately because of a new naming convention for such viruses, a reoccurrence of the “swine flu” label is unlikely. (See sidebar.)
An unusual case surfaced in Wisconsin, involving a triple-reassortant influenza virus known to circulate in pigs but not in people. The infected person had occupational contact with swine prior to becoming ill. Centers for Disease Control and Prevention testing confirmed that it involved a new variant, having acquired the matrix (M) gene from the 2009 H1N1 pandemic virus. “This reassortment has been found in U.S. swine since 2010. However, this is the first time this genetic sequence has been detected in a human,” CDC reports.
Good news for all is that the variant, now known as H1N1v, did not spread further. CDC reports no human-to-human transmission.
Since last August through more recent months, another variant surfaced. It includes the 2009 H1N1 virus matrix (M) gene in triple reassortant H3N2 viruses. It is now labeled influenza A (H3N2)v or H3N2v. This influenza virus has infected 12 people, with cases occurring in West Virginia, Indiana, Iowa, Maine and Pennsylvania. Eleven of the 12 cases occurred in children, according to CDC. Five of those cases had no history of direct exposure to swine, and all individuals recovered.
“The lack of swine exposure combined with current epidemiological data suggest limited human-to-human transmission of H3N2v may have occurred,” says Phil Gauger, DVM, veterinary diagnostic and production animal medicine, Iowa State University.
Overall, it appears that H3N2v is no more virulent than other human seasonal influenza viruses. Gauger also points out that USDA’s anonymous swine surveillance system has identified H3N2v in swine, but it has not been associated with increased clinical disease. That’s more good news. However, the full implication of these viruses in the swine population is unknown, he adds.
While the 2009 H1N1 virus likely moved from humans to swine, CDC points out that it’s not surprising to see influenza viruses swap genes and move around. “Although the majority of human infections with animal influenza viruses do not result in human-to-human transmission, each case must be investigated fully,” CDC notes.
Those investigation efforts include state, local, and federal public and animal health officials. It also includes you, your employees and swine veterinarians. That means monitoring the health of your animals as well as people working with them, says Jennifer Koeman, National Pork Board’s director of producer and public health.
It also means participating in USDA’s swine influenza surveillance plan, which launched in October 2010. The voluntary program got off to a slow and rather skeptical start, but the comfort level and program awareness have improved.
“When comparing submission numbers from 2010 to 2011, the trend clearly shows greater participation,” Koeman says. USDA publishes quarterly reports tracking the number of herds from which samples are submitted. (For more, go to http://tinyurl.com/75jcqep.) The samples are submitted on a herd-only basis (not per pig) because the goal is to gather population information.
“If a producer’s pigs present respiratory symptoms with influenza-like illness, the producer simply works with his/her veterinarian to submit the samples to the diagnostic lab as usual,” points out Lisa Becton, DVM, NBP’s swine health information and research director. At the lab, the sample will be evaluated and tested for influenza and other diseases if appropriate. If the sample is positive for influenza, it’s eligible for the surveillance plan, which includes further diagnostics.
“A producer can opt out, and this occurs in writing when he submits samples to the lab,” Becton notes. “There are still folks who choose not to provide information, but many folks are going back to ‘business as usual’ when submitting samples for respiratory cases.”
Samples included in the surveillance plan are run anonymously with only the state and date recorded publically. A producer can request (in writing) to make the herd’s demographic information available to USDA NSU for surveillance purposes only. This does allow for more accurate monitoring of trends and patterns.
Beyond tracking the human/animal virus evolution and interaction, the swine influenza surveillance program has direct benefits to pork producers, including:
• Providing information to help develop and update swine influenza virus vaccines.
• Improving the reliability of SIV diagnostic testing.
• Gathering information on circulating SIVs that can be used to improve herd-health protocols.
Beyond participating in the influenza surveillance program, there are numerous other steps to apply on the farm to keep pigs and people healthy. Influenza vaccination for workers and pigs is a priority. Other biosecurity, personnel and visitor protocols can be found on NPB's website at pork.org/resources/default.aspx.
No More Swine Flu
In 2009, the U.S. pork industry paid an unfortunate price when 2009 influenza A (H1N1) was mislabeled “swine flu.”
The good news is that the Centers for Disease Control and Prevention and the World Health Organization have adopted a new naming convention for variant influenza viruses. Those are viruses that contain genes from multiple species — for example avian, swine and human. That was the case in 2009 as well, but because that virus carried two swine influenza virus segments it prompted the label “swine flu.”
Now, such variant viruses will be designated by a V and the strain. For example, the 12 cases cited in the article here involved influenza A (H3N2)v.
“The new naming convention uses more accurate terminology because these viruses contain genes from a number of species and influenza viruses,” says Jennifer Koeman, National Pork Board’s director of producer and public health. It doesn’t put the emphasis, or burden, on any one of them, and influenza viruses are contiuously changing.
“It more accurately reflects the composition of the virus,” Koeman adds. “It also reinforces the message to consumers that you cannot get the flu from handling pork and that pork products are safe.”
NPB, the National Pork Producers Council and American Association of Swine Veterinarians all work closely with USDA and CDC to share and evaluate public and swine influenza surveillance information. “We are very supportive of the new naming convention,” Koeman says.