CategoryPublic Health - Influenza
Date Full Report Received07/01/2018
Date Abstract Report Received07/01/2018
Funded ByNational Pork Board
Pigs play a critical role in the ecology and epidemiology of influenza A viruses (IAVs) by serving as a source of novel reassortant viruses infecting humans. Agricultural fairs and livestock exhibitions create an environment conducive to zoonotic IAV transmission by commingling pigs and people for a prolonged period, resulting in a dramatic increase in the number of documented variant influenza A cases in people during 2011-2018. The epidemiological investigations into the 306 reported human cases of variant H3N2 influenza A (H3N2v) that occurred in 2012 linked the majority of them to human-swine exposure occurring at fairs. Research conducted by this study team provided molecular confirmation of zoonotic H3N2v transmission at county fairs in addition to evidence that IAV infections are common among apparently healthy swine at agricultural fairs.
H3N2v outbreaks in 2011-2016 show that swine infected with IAV at fairs and livestock exhibitions are a public health threat. Reducing zoonotic transmission of IAV between pigs and people is crucial to both agriculture and public health. Swine industry leaders and public health officials are seeking strategies to reduce intra- and inter- species transmission of IAV at swine exhibitions. The ultimate objective of this project was to provide new knowledge and insight into the dynamics of IAVs circulating in exhibition swine that can be used to make evidence based recommendations to prevent cases, outbreaks, epidemics, and/or pandemics caused by swine-to-human transmission of IAV occurring at agricultural fairs and livestock exhibitions. In order to achieve this objective, three specific aims were investigated:
1) Estimate influenza A virus prevalence in exhibition swine at jackpot shows.
The scientific community currently has limited data about IAV activity among exhibition swine at jackpot shows. Last year we hypothesized that the prevalence of IAV at jackpot shows would be <5%, but overall we detected a 12% IAV prevalence in 3,754 pigs sampled across 21 jackpot shows during 2016. Interestingly, in one jackpot show we detected IAV in 47% of the pigs tested. While we found a higher IAV prevalence than expected, findings cannot be interpreted as normal or abnormal without additional data. Detecting 461 IAVs during the first year of this project indicates one year of surveillance is simply inadequate to estimate the IAV prevalence in exhibition swine at jackpot shows. In addition to providing insights into this understudied portion of the exhibition swine lifecycle, this aim aids the influenza research community by contributing data from active IAV surveillance in clinically healthy pigs, an identified gap in current swine IAV surveillance programs.
2) Evaluate influenza A virus evolution and transmission in exhibition swine.
Previous work has demonstrated that it is common to find similar IAVs at several fairs across a large geographic area. We suspect that pigs are becoming infected with IAV at jackpot shows, start shedding virus after the show, perpetuate viral transmission between additional naïve exhibition swine at future jackpot shows which eventually leads to index cases at local fairs. We hypothesized the IAV strains found in pigs at jackpot shows would be genomically similar to those strains found in pigs at agricultural fairs during the same year. Sequences of the IAV isolates recovered from pigs during Aim 1 are being used to test this hypothesis. While we are still performing the sequencing of viral isolates recovered during 2016, we have identified a H3N2 virus from a pig at a June 2016 jackpot show that is 99.95% identical (i.e. the same) to two of the 2016 human H3N2v cases. This isolate was recovered approximately one month prior to the start of the fair where the humans became infected, indicating the jackpot show likely played a role in propagating and disseminating the virus. It appears that controlling IAV at jackpot shows could have a major impact on IAV transmission within the exhibition swine population. Thus, decreased IAV transmission during jackpot shows would likely reduce the IAV prevalence at downstream agricultural fairs providing protection to public health.
3) Evaluate compliance with recommendations from animal and public health officials.
This new aim for 2017 is based on the feedback received from the Public Health Committee. The National Assembly of State Animal Health Officials and National Association of State Public Health Veterinarians have released several recommendations for swine exhibitors and show organizers in a document entitled Measures to Minimize Influenza Transmission at Swine Exhibitions. We hypothesize that while recommendations are being made, swine exhibitors are either unaware or reluctant to adopt the changes in recommended swine management practices. Understanding exhibitors’ perception of the recommendations and barriers to adoption is critical because exhibitor compliance with proposed mitigation strategies is key to decreasing the disease burden in swine, thus reducing the risk of IAV transmission from pigs to people.
In order to estimate the prevalence of IAV among swine at jackpot shows, nasal wipes were collected from 53-600 pigs per show at 22 selected jackpot shows, resulting in 3,665 samples. Nasal wipes were used in this study because, although not as sensitive as nasal swabs, they provide a sample collection method without the need for pig restraint. Based on the estimated distribution of exhibition swine in the Midwestern United States, jackpot shows occurring in Iowa, Illinois, Indiana, Ohio, Kentucky, and Michigan were included. The shows will never be identified by name and will not appear by name in any publication. Exhibitor identities were not collected thus results could never be traced back to any of the animals, individuals, or farms.
Overall, 5% of samples tested from swine at jackpot shows were positive for viable influenza A virus. In comparison, 9.5% of exhibition swine tested during the 2017 agricultural fair season were shedding active influenza A virus. The reduced prevalence of IAV in pigs within the jackpot circuit as compared to agricultural fairs could be due to the shortened period of time in which the pigs are co-mingled. A majority of jackpot shows are one to two days, with many pigs being housed within trailers rather than exhibition barns to minimize contact with other animals and their infectious diseases. A decrease in IAV prevalence due to the shortened show duration could be extrapolated as the effects of implementing a 72 hour rule at agricultural fairs, as is recommended in the “Measures to Minimize Influenza at Swine Exhibitions” document. Disseminating related data through relationships built through sample collection activities could elicit change throughout the swine exhibition network as individuals see the impact paradigm shifts could have on animal and public health at their local swine exhibitions.
For more information regarding the outcome of this study please visit our website at www.go.osu.edu/vetfluresearch