Tara Donovan, DVM
It’s fall here in Wisconsin and with that come cool evenings and mornings, the start of school for my kids, fair time, and inevitably for a swine veterinarian, clinically affected pigs with influenza. This week all of these topics converged and thus gave me a great opportunity to express my thoughts in this message.
There is a recent increase in human cases of influenza associated with a variant H3N2 (H3N2v) virus at local and state fairs throughout the Midwest. The cases of influenza have been linked to contact with pigs and are primarily in children. Although most swine influenza viruses infect swine and human influenza viruses infect humans, we know that influenza viruses are capable of moving across the two species. Scientists report that this particular variant virus is a result of the 2009 H1N1 pandemic strain infecting pigs after the widespread human infections. The pandemic H1N1 has subsequently combined with the H3N2 virus endemic in the US swine population, creating a progeny virus, H3N2v. This is not a pandemic influenza: it is not spreading among humans, only from pigs to humans. As a result, the advice from the Centers for Disease Control (CDC) is to prevent pig-to-human contact or reduce the chance of such contact or both and to take precautionary sanitation measures if you are in contact with pigs. Inevitably, county and state fairs are places where many people not normally in contact with pigs are exposed, and thus the influx of these cases. There has been a plethora of information shared and recommendations outlined concerning this issue, and in my opinion, good communication between the CDC, human- and animal-health professionals, fair officials, and news media. Thanks to everyone who has spent time and effort in this process on behalf of our industry.
The fair in my county is late in the season, occurring in the first week of September, the same time school gets underway. There was an announcement from the principal of my children’s school, “Important Health Alert for the Fair!” advising parents to be careful when attending our county fair, as a strain of influenza, H3N2v, affecting children was being transmitted to them by pigs. The announcement recommended using hand sanitizer, washing hands, not eating while visiting the animal barns, and staying home if you feel ill.
Of course some angst regarding this issue is in the belly of every swine veterinarian and producer, as the impact of the pandemic H1N1 influenza virus on our industry left a permanent scar. This is indeed a reminder that influenza continues to be a threat to our pigs’ health, human health, and our industry.
The last influenza reminder that occurred in the same week was a conversation that I had with another swine veterinarian. We were reviewing a summary of influenza diagnostic results and genetic typing from our system’s swine herds and contemplating which virus strains to include in or eliminate from our autogenous vaccines. This time of year we typically see an increase in influenza cases, so to be prepared, we try to determine if changes should be made in our vaccine strains as a preventative step. Our discussion entailed the concerns of having a virus strain in the vaccine that does not match the one that infects the pigs, which then causes vaccine-associated enhanced respiratory disease, a phenomenon reported by scientists. We attempt to compare our results with information we can get from the diagnostic laboratories reporting swine influenza strains and the trends they are observing across the industry, as well as information reported from the USDA Swine Surveillance Program.1
There is no consistency in the use of swine influenza vaccine among swine herds or in the recommendations of their veterinarians. These discrepancies arise from the vaccine’s inconsistent efficacy, the logistical and regulatory challenges to making quick strain changes in the vaccine, similar challenges in quickly detecting changes in genetic strains, and unrealistic confidence in the vaccine’s ability to prevent and control clinical disease.
We have new swine influenza viruses evolving at a rapid pace. How are we keeping up with technology in order to combat this disease in our herds? Some progress in swine influenza vaccine technology and new diagnostic capabilities have helped us know more about influenza virus evolution. We have a little more flexibility in commercial-vaccine strain substitution; we have frequent use of farm-specific killed autogenous vaccine and some newer technology using recombinant viral subunit vaccines and vector particle vaccines which can be produced more quickly to adapt to new circulating strains. There is ongoing research in both human and animal vaccines. With all this said, we continue to have severe clinical cases of swine influenza and experience rapid change in the virus in our pig populations.
As practitioners, we need more options for our producers. We need to understand the virus in our pig populations, transmission of the virus, and how we can stop or minimize transmission. We need help in easing the regulatory process for vaccines that will be more effective. We need continued and increased funding for research in swine influenza. We need continued funding for the surveillance program that is in its infancy, and we need to understand how to use the information from this program to help us predict and interpret changes in the swine influenza virus. And lastly, and perhaps most concerning, there is the risk in the human-swine interface that affects confidence in pork as a protein choice for US and international consumers. We need continued communication, networking, and education in the human and animal medical professions, the media, food suppliers, policy makers, and our consumers.
Reference
1. United States Department of Agriculture. Animal and Plant Health Inspection Service. Animal Health. Swine Influenza Surveillance. 2012. Available at: http://www.aphis.usda.gov/animal _health/animal_dis_spec/swine/siv_ surveillance.shtml. Accessed 10 September 2012.