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 2011-2016. 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 proposal is 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 had little data about IAV activity among exhibition swine at jackpot shows. While it is common to find > 75% of the pigs infected at agricultural fairs with IAV, we believed that jackpot shows, due to the short exhibition period (1-2 days), would not provide enough time for IAV amplification within the swine population as occurs at longer agricultural fairs (3-10 days). Therefore, we hypothesized that the prevalence of IAV at jackpot shows would be <5%. Animal and public health officials have recommended that swine exhibitions be shortened to less than 72 hours to limit influenza amplification. By sampling pigs at short duration jackpot shows, this aim will directly provide data to evaluate the recommendation of shortening swine exhibitions.
2) Evaluate influenza A virus evolution and transmission in exhibition swine.
Our previous work has demonstrated that it is common to find similar IAVs at several fairs across a large geographic area (across states). We suspected that pigs were becoming infected with IAV at jackpot shows, subsequently start shedding virus after the show thus perpetuating viral transmission between additional naïve exhibition swine at future jackpot shows and local agricultural fairs. Thus, we hypothesized the IAV strains found in pigs at jackpot shows would be genomically the same as those strains found in pigs at agricultural fairs during the same year.
3) Describe geographic movement of exhibition swine for competition.
Pigs can be transported long distances for the purpose of competition in livestock shows, which may facilitate rapid and wide-spread dissemination of IAV. The extent to which exhibition pigs move for competition has been poorly defined but may be a critical key in understanding the natural history of IAV in exhibition swine. We sought to better define the extent of swine movement for the purposes of exhibition by capturing the zip code of residence of jackpot show exhibitors.
In order to estimate the prevalence of IAV among swine at jackpot shows, nasal wipes were collected from 85-600 pigs per show at 21 selected jackpot shows, resulting in a total of 3,754 samples representing pigs from 37 states. 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. Exhibitor identities were not collected thus results could never be traced back to any of the animals, individuals, or farms.
We hypothesized that the prevalence of IAV at jackpot shows would be <5%, but overall we detected a 12% IAV prevalence with PCR 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 data from additional years. Detecting 461 IAVs during the first year of this project indicates one year of surveillance is simply inadequate to accurately estimate the IAV prevalence in exhibition swine at jackpot shows. Therefore, the project is being continued in 2017.
Overall, viable influenza A virus was recovered from 3% from swine at jackpot shows. In comparison, 12.3% influenza A virus was isolated from 12.3% of swine tested during the 2016 agricultural fair season. 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 comingled. A majority of jackpot shows are one to two days, with many pigs being housed in 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 targeted messages through relationships built via this project could elicit change throughout the swine exhibition network as individuals see the impact paradigm shifts could have on animal and public health at local levels.
For more information regarding the outcome of this study please visit our website at www.go.osu.edu/vetfluresearch