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. 2025 Apr 1:12:1523981.
doi: 10.3389/fvets.2025.1523981. eCollection 2025.

Estimating the risk of zoonotic transmission of swine influenza A variant during agricultural fairs in the United States: a mathematical modeling

Dana C Pittman Ratterree  1 , Sapna Chitlapilly Dass  2 , Martial L Ndeffo-Mbah  1   3
Affiliations

Estimating the risk of zoonotic transmission of swine influenza A variant during agricultural fairs in the United States: a mathematical modeling

Dana C Pittman Ratterree et al. Front Vet Sci. .

Abstract

Introduction: Agricultural fairs offer a unique interface between humans and swine. We investigate the transmissibility of influenza A variant from pigs to humans using epidemiological data from a 2011 zoonotic outbreak of an influenza H3N2 variant during an agricultural county fair in Pennsylvania.

Methods: We developed a mathematical model for the transmission of a swine influenza pathogen among pigs and humans at an agricultural fair. We fitted our model to the outbreak data to estimate zoonotic transmissibility. We considered nine data-driven scenarios of swine-to-swine basic reproductive number (R0) and the number of infected pigs at the start of the fair, and we simulated the zoonotic outbreak dynamics.

Results: We estimated the probability of swine-to-human H3N2v transmission per minute of swine contact for which our model best fitted the data. The probability of transmission of H3N2v per minute of contact with swine among club members was estimated to vary from 0.029 (95% confidence interval (CI): 0.028-0.030), when R0 = 2 with 1 initially infected pig, to 0.00099 (0.00095-0.00102), when R0 = 6 with 5 initially infected pigs. For attendees, we showed that the probability equals 0.0168 (95% CI: 0.0167-0.0169), when R0 = 2 with 1 initially infected pig, and 0.00371 (95% CI: 0.00368-0.00373), when R0 = 2 with 5 initially infected pigs. For all scenarios, we estimated H3N2v infection prevalence among club members and attendees to average 12 and 0.7%, respectively.

Discussion: These results show that the transmission risk may vary substantially between club members and attendees and with the underlying disease transmission among pigs. Although fair attendees may have a small transmissibility risk, annual fair attendees represent a large population likely to experience zoonotic events and facilitate the emergence of a potential pandemic influenza variant.

Keywords: agricultural fair; mathematical modeling; swine influenza; transmission risk; zoonotic events.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The author(s) declared that they were an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision.

Figures

Figure 1
Figure 1
Compartmental diagram for the transmission of influenza A variant between swine and human population. Created in BioRender. Pittman, D. (2025) https://BioRender.com/w17r576.
Figure 2
Figure 2
(A) Model fitting results using maximum likelihood estimation (MLE) when R0 is 2 and 5 initially infected pigs. (B) Model fitting results using MLE when R0 is 4 and 5 initially infected pigs. (C) Model fitting results using MLE when R0 is 6 and 5 initially infected pigs.
Figure 3
Figure 3
(A) Probability of Transmission estimate for R0 = 2 for Club member Population with 95% confidence interval (CI). (B) Probability of Transmission estimate for R0 = 4 for Club member Population with 95% CI. (C) Probability of Transmission estimate for R0 = 6 for Club member Population with 95% CI.
Figure 4
Figure 4
Stochastic simulation of the infection prevalence by population for five initially infected pigs.
See this image and copyright information in PMC

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