PhD Defence Ceremony by Ms Yali Si
Dept. of Natural Resources
Title of defence:
Avian influenza and migratory birds: a spatial ecological perspective
Summary
The global spread of highly pathogenic avian influenza (HPAI) H5N1 poses a significant threat to public health. An efficient surveillance and disease control system relies on our understanding of the ecology of the HPAI H5N1 virus. Domestic poultry and wild birds (mainly waterfowl) are considered as the spreading agents. The role of poultry in the spread of the virus is relatively well understood. However, the role of migratory waterfowl, especially in long-distance transmission, requires further investigation. Environmental factors influencing the occurrence of HPAI H5N1 in wild birds are currently unknown. Furthermore, the spatio-temporal occurrence of waterfowl has not yet been quantified at regional and higher scales. To generate up-to-date, accurate measures of the relevant environmental conditions over large geographic regions, more effort in remote sensing is required.
The aim of this study is to investigate the interactions among the occurrence of HPAI H5N1, the distribution of migratory waterfowl, and environmental factors, from a spatial-ecological perspective.
We find that the outbreak pattern of HPAI H5N1 is highly correlated with waterfowl migration patterns, suggesting that migratory waterfowl play an important role in the global spread of HPAI H5N1 over both short and long distances. Furthermore, wild birds instead of poultry were the main spreading agent causing the 2005-2008 HPAI H5N1 outbreaks in European wild birds. HPAI H5N1 occurrence in wild birds in Europe is influenced by the availability of food resources and facilitated by increased temperatures and reduced precipitation. The spatial distribution of waterfowl at a habitat level is determined by food availability (i.e., grasses with high quality and intermediate quantity), distance to roosts, and the presence of refuges. We use a single-biome approach, which specifically focuses on grassland, rather than the conventional multi-biome approach, which looks at vegetation in general. The single-biome approach performs consistently better and yields an intermediate accuracy of forage quantity and quality retrieval. The estimated spatio-temporal variation of forage quantity and quality is placed in the context of migratory waterfowl grazing, which allows monitoring the availability of food resources continentally. Subsequently, the migration patterns can be quantified and these can further assist the risk prediction of HPAI H5N1 outbreaks.
This study has shown the value of taking a spatial-ecological perspective to the understanding of the interactions among HPAI H5N1 occurrence, waterfowl distribution, and environmental factors. Our findings can be used to improve HPAI H5N1 surveillance and assist in controlling the disease in an ever-changing environment.
Biography
Yali Si was born on 15 September 1982 in Hubei Province and grew up in Henan Province, China. In 1999, she went to Henan Agricultural University and studied Land Resource Management, where she received her bachelor degree with distinction in 2003. She then moved to Wuhan University in 2004 and enrolled in a joint master’s programme between Wuhan University and the International Institute for Geo-information Science and Earth Observation (ITC) in the Netherlands. She completed her thesis with distinction in March 2006 and received her M.Sc. degree in Geo-information for Natural Resources and Environment Management. In 2006, she was awarded a four-year doctoral scholarship from the China Scholarship Council, with partial financial support from ITC. She then moved to the Netherlands again in 2007 and started her Ph.D. research at ITC and Wageningen University, which resulted in her doctoral thesis “avian influenza and migratory birds: a spatial-ecological perspective”. Her research interests include spatial ecology, spatial epidemiology, ecosystem modelling, remote sensing of vegetation, and global change ecology.
Si, Y., Skidmore, A.K. (Promotor) , Prins, H.H.T. (Promotor) and Wang, T.J. (assistant promotor) (2011) Avian influenza and migratory birds : a spatial - ecological perspective. PhD thesis University of Twente; summaries in Dutch and English. ITC Dissertation 188, ISBN: 978-90-6164-308-1.
| Timesheet | |
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| Event starts: | Thursday 16 June 2011 at 14:30 |
| Venue: | University of Twente, Waaier room 4 |
| City where event takes place: | Enschede |
| Country where event takes place: | Netherlands |