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Estimating Contact Structure among Wild Pigs: Implications for African Swine Fever Transmission and Management

Anni Yang1, 2*, Peter E. Schlichting3, Mark Wilber4, Bethany Wight5, Wesley Anderson5, Sarah Chinn3, Ryan S. Miller2, Kurt C. VerCauteren2, James C. Beasley3, Raoul K. Boughton5, George Wittemyer1 and Kim M. Pepin2
  • 1 Department of Fish, Wildlife, and Conservation Biology, Warner College of Natural Resources, Colorado State University, United States
  • 2 National Wildlife Research Center, Animal and Plant Health Inspection Service, United States
  • 3 Savannah River Ecology Laboratory, University of Georgia, United States
  • 4 Department of Ecology Evolution and Marine Biology, University of California, United States
  • 5 Department of Wildlife Ecology and Conservation, University of Florida, United States

African swine fever (ASF), caused by the African swine fever virus (ASFV), is a highly contagious disease that causes hemorrhagic fever and almost 100 percent mortality in pigs (Zhou et al., 2018). Transmission of the disease occurs among domestic (Sus scrofa domesticus) and wild pigs (Sus scrofa) via direct contact, insect vectors (mainly soft ticks of the Ornithodoros species) or other indirect mechanisms related to environmental factors or dead carcasses (Guinat et al., 2016). Wild pigs are an invasive, socially-structured species in the US that pose serious health threats to the domestic swine industry because of their ability to transmit devastating swine diseases such as ASF. Contact rates among individuals in wild pig populations can vary widely, affecting the spatiotemporal patterns of disease (Pepin et al., 2016). Understanding the factors that shape variation in the contact rates and structure among wild pig populations is essential for planning effective control and management of ASF (Pepin et al., 2016). In this study, we captured and deployed proximity loggers on 22 wild pigs on the US Department of Energy’s Savannah River Site (SRS) in South Carolina and 27 at the MacArthur Agro-ecology Research Center (MAERC), a division of Archbold Biological Station, in Florida in February 2017 – January 2018. In coordination, nine wild pig baiting stations were set up with proximity loggers at SRS in South Carolina during July 3, 2017 – August 28, 2017. In other recent work, we developed a method for inferring contact structure within and among species that included direct and indirect contact mechanisms within a single network (Wilber et al., 2019). Here, we applied this approach to analyze the contact structure in wild pigs and to estimate the effects of different management interventions on the contact networks to infer their effects on the transmission of ASF. Specifically, we 1) examined the effects of season, demographic factors (i.e. sex, age, and social group membership), and distance among home ranges on the contact structure of wild pig populations; 2) quantified the role of group- and individual-level heterogeneity in contact structure of wild pigs; 3) identified the influence of wild pig removals on contact structure; and 4) estimated how baiting impacted contacts among wild pigs. Our findings suggest contact structure in wild pig populations is strongly driven by demographic characteristics. The higher contact rates between female adults and juveniles and subadults confirm the matrilineal nature of wild pig social structure. Also, group-, and individual-level heterogeneity disproportionately affect the contact network of wild pigs. Substantial reductions of the wild pig population reduced between-group contact rates significantly and increased within-group contacts in wild pigs. Bait put out for wild pigs increased the between-group contacts. Our study provides quantitative predictions for how wild pig ecology and management impact transmission rates of ASF, thus providing important guidance for safely managing wild pigs in the US and responding to foreign animal disease threats.

Acknowledgements

The logistical and financial support of the research was supplied by the USDA- APHIS National Feral Swine Damage Management Program. Field work at SRS also was partially supported by the US DoE under Award Number DE-EM0004391 to the University of Georgia (UGA) Research Foundation. We are grateful for the assistance from the field teams from the Savannah River Ecology Laboratory at the UGA and the Range Cattle Research and Education Center at the University of Florida for data collection.

References

Guinat, C., Gogin, A., Blome, S., Keil, G., Pollin, R., Pfeiffer, D. U., & Dixon, L. (2016). Transmission routes of African swine fever virus to domestic pigs: current knowledge and future research directions. The Veterinary Record, 178(11), 262. Pepin, K. M., Davis, A. J., Beasley, J., Boughton, R., Campbell, T., Cooper, S. M., … Wisely, S. M. (2016). Contact heterogeneities in feral swine: implications for disease management and future research. Ecosphere, 7(3), e01230. Wilber, M. Q., Pepin, K. M., Campa III, H., Hygnstrom, S. E., Lavelle, M. J., Xifara, T., … Webb, C. T. (2019). Modeling multi‐species and multi‐mode contact networks: implications for persistence of bovine tuberculosis at the wildlife‐livestock interface. Journal of Applied Ecology. Zhou, X., Li, N., Luo, Y., Liu, Y., Miao, F., Chen, T., … Tian, K. (2018). Emergence of African swine fever in China, 2018. Transboundary and Emerging Diseases, 65(6), 1482–1484.

Keywords: :African swine fever (ASF),, Contact heterogeneity, network modeling, Wild pigs, wild pig management

Conference: GeoVet 2019. Novel spatio-temporal approaches in the era of Big Data, Davis, United States, 8 Oct - 10 Oct, 2019.

Presentation Type: Regular oral presentation

Topic: Special topic on African Swine Fever (ASF)

Citation: Yang A, Schlichting PE, Wilber M, Wight B, Anderson W, Chinn S, Miller RS, VerCauteren KC, Beasley JC, Boughton RK, Wittemyer G and Pepin KM (2019). Estimating Contact Structure among Wild Pigs: Implications for African Swine Fever Transmission and Management. Front. Vet. Sci. Conference Abstract: GeoVet 2019. Novel spatio-temporal approaches in the era of Big Data. doi: 10.3389/conf.fvets.2019.05.00113

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Received: 20 Jun 2019; Published Online: 27 Sep 2019.

* Correspondence: Dr. Anni Yang, Department of Fish, Wildlife, and Conservation Biology, Warner College of Natural Resources, Colorado State University, Fort Collins, Colorado, 80523-1474, United States, yangann1@colostate.edu