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School of Environment and Life Sciences

Dr Stephen Parnell

Reader in Spatial Epidemiology


I graduated with a BSc (Hons) in Ecological Science from the University of Edinburgh in 2001. In my final year dissertation I used GIS (Geographic Information Systems) and spatial statistics to analyse plant disease epidemic data. Following graduation I spent a year at the BBSRC agricultural institute Rothamsted Research in the Statistics Unit where I became increasingly interested in the use of quantitative methods, particularly in epidemic spread modelling. 

I went on to complete my PhD at the University of Cambridge in mathematical biology where my thesis focused on the population dynamics and management of pesticide resistance in crop protection.  Following this I spent two years as a Postdoctoral researcher at the US Department of Agriculture (USDA) in Florida where I developed models of invasive diseases of citrus and worked closely with the Animal and Plant Health Inspection Service (APHIS) to inform disease surveillance strategies.  I then spent seven years as a Research Scientist and epidemic modeller at the Rothamsted Research before moving to Salford as Lecturer in Spatial Epidemiology in October 2014.


I contribute to a wide range of modules across undergraduate and postgraduate programmes in the School of Environment and Life Sciences. I lead a final year undergraduate module ‘Modelling Environmental Systems’ and I also teach spatial analysis methods on the MSc in Geographical Information Systems (GIS) which is run jointly between Salford and Manchester Metropolitan University (UNIGIS). 

Research Interests

My research aims to better understand the processes that drive the spread of plant disease epidemics with a practical focus on improving disease surveillance strategies.  As international trade and travel continues to increase, more plants are being shipped around the world, and more pests and diseases are showing up in unexpected places. Recent high profile cases in the UK include Ash Dieback disease, but this is a global issue, affecting agricultural crops and natural environments everywhere.

I work closely with national and international bodies such as Defra, the US Department of Agriculture and the European Food Safety Authority to provide advice on surveillance strategies. We use epidemic modelling approaches to help identify when and where disease risk is highest and thus where surveillance resources should be targeted.

We address practical questions such as: How should we design a surveillance programme to maximise the probability to detect an epidemic soon after it begins? How can we be sure that a region is disease free if nothing is detected in a sampling program? What is the most cost-effective combination of detection and diagnostic technologies against a particular pest or disease threat? How can we make best use of citizen science efforts to detect pests and diseases?

Qualifications and Memberships

PhD in Mathematical Biology, University of Cambridge (2005)

BSc Ecological Science (Resource Management Hons), University of Edinburgh (2001)

Member of the European Food Safety Authority (EFSA) Plant Health Panel (2014-current)

Senior Editor of the journal Phytopathology (2015-current)


Brown, N., van den Bosch, F., Parnell S. and Denman S. 2017. Integrating regulatory surveys and citizen science to map outbreaks of forest diseases: acute oak decline in England and Wales. Proceedings of the Royal Society B. Print ISSN: 0962-8452.

Parnell, S., van den Bosch F., Gottwald, T.R. and Gilligan C.A. 2017. Surveillance for emerging plant disease; an epidemiological perspective. Annual Review of Phytopathology 55:25 1–25.

Hyatt-Twynam, S.R., Parnell, S., Stutt, R. O. J. H., Gottwald, T.R., Gilligan, C.A. and Cunniffe, N.J. 2017. Epidemiologically-motivated control strategies to manage outbreaks of invading plant disease. New Phytologist 214(3): 1317-1329.

Alonso-Chavez V., Parnell S. and van den Bosch, F. 2016. Monitoring invasive pathogens in plant nurseries for early-detection and to minimise the probability of escape. Journal of Theoretical Biology 407:290-302. doi: 10.1016/j.jtbi.2016.07.041. Epub 2016 Jul 28.

Milne A., Bell J. Hutchison W., van den Bosch F., Mitchell P., Crowder D., Parnell S., Whitmore A.P. 2015. The effect of farmer decisions on the control of pests: a billion dollar ecology game, PLOS computational biology. Doi:10.1371/journal.pcbi.1004483.

Alonso-Chavez V., Parnell S. and van den Bosch, F. 2015. Designing strategies for epidemic control in a tree nursery: the case of ash dieback in the UK. Forests 6 (11), 4135-4145.

Parnell S., Gottwald T.R, Cunniffe N.J., Alonso-Chavez V., van den Bosch F. 2015. Early detection surveillance for an emerging plant pathogen: a rule of thumb to predict prevalence at first discovery. Proceedings of the Royal Society B 282 (1814), 20151478.

Cunniffe N.J., Koskella B., Metcalf C.J.E, Parnell S, Gottwald T.R. and Gilligan C.A.  2015.  Thirteen challenges in modelling plant diseases. Epidemics 10: 6-10.

Parry, M. Gibson, G.J., Parnell, S., Gottwald, T.R., Irey, M.S., Gast, T.C. and Gilligan, C.A. 2014. Bayesian inference for an emerging arboreal epidemic in the presence of control. Proceedings of the National Academy of Sciences (PNAS) 111(17): 6258-6262.

Parnell, S., Gottwald, T.R., Riley, T.R. and van den Bosch, F. 2014. A generic risk-based surveying method for invading plant pathogens. Ecological Applications 24:779–790.

Gottwald, T.R., Wierenga, E., Luo, W. and Parnell, S. Epidemiology of Plum pox ‘D’ strain in Canada and the USA. 2013. Canadian Journal of Plant Pathology 35: 442-457.

Bock, C., Wood, B., van den Bosch, F., Parnell, S. and Gottwald, T.R. 2013. The Effect of Horsfall-Barratt Category Size on the Accuracy and Reliability of Estimates of Pecan Scab Severity. Plant Disease 97: 797-806.

Parnell, S., Gottwald, T.R., Gilks, W.R. and van den Bosch, F. 2012. Estimating the incidence of an epidemic when it is first discovered and the design of early detection monitoring. Journal of Theoretical Biology 305:30-36.

Luo, W., Pietravalle, S., Parnell, S., van den Bosch, F., Gottwald, T.R., Irey, M.S., Parker, S.R. 2012. An improved regulatory sampling method for mapping and representing plant disease from a limited number of samples. Epidemics 4:68-77. 

Parnell, S., Gottwald, T.R., Irey, M.S., Luo, W., and van den Bosch, F. 2011 A stochastic optimisation method to estimate the spatial distribution of a plant pathogen from a sample. Phytopathology 101:1184-1190.

Bock, C.H., Gottwald, T.R., Parker, P.E., Cook, A.Z., Ferrandino, F., van den Bosch, F, and Parnell, S. 2010. Some consequences of using the Horsfall-Barratt scale for hypothesis testing. Phytopathology 100:1030-1041. 

Parnell, S., Gilligan, C.A., Gottwald, T.R., Cunniffe, N., and van den Bosch, F. 2010. The effect of landscape pattern on the eradication of an invading epidemic. Phytopathology 100:638-644.

Parnell, S., Gilligan, C.A., van den Bosch, F. and Gottwald, T.R. 2009. Optimal strategies for the eradication of Asiatic citrus canker in heterogeneous host landscapes. Phytopathology 99:1370-1376.

Bock, C.H., Gottwald, T.R., Parker, P.E., Cook, A.Z., Ferrandino, F., Parnell, S., and van den Bosch, F. 2009. The Horsfall-Barrat scale and severity estimates of citrus canker. European Journal of Plant Pathology 125:23-38.

Parnell, S., Gilligan, C.A., Lucas, J.A., Bock, C.H., and van den Bosch, F. 2008. Changes in fungicide sensitivity and relative species abundance in Oculimacula yallundae and O. acuformis populations (eyespot disease of cereals) in Western Europe. Plant Pathology 57:509-517.

Parnell, S., van den Bosch, F., and Gilligan, C.A. 2006. Large-scale fungicide spray heterogeneity and the regional spread of resistant pathogen strains. Phytopathology 96:549-555.

Parnell, S., Gilligan, C. A., and van den Bosch, F. 2005. Small-scale fungicide spray heterogeneity and the coexistence of resistant and sensitive pathogen strains. Phytopathology 95:632-639.