Model based analysis of field data on CSFV transmission & persistence in Wild Boar

FP7 funded research project CSF_goDIVA. The aim of the consortium is to improve control of CSF in domestic pigs and wild boar. The main goal is to develop a vaccine that combines three basic features:

  • Effective immunisation of pigs and wild boar against infection with Classical Swine Fever Virus (CSFV)
  • Availability of diagnostics that differenciate immunity due to vaccination from those caused by a wild-type infection (DIVA principle)
  • Oral applicability for mass vaccination of wild boar populations

The Work Package 7 addresses the development of sustainable and economic strategies for mass vaccination of wild boar in the field. The EcoEpi contributes to the task based on simulation experiments with its spatially-explicit individual-based model (Kramer-Schadt et al. 2009).
The modelling is performed by Martin Lange (PhD-student at the OESA).

Classical Swine Fever Virus and Wild Boar

Wildlife pathogens, like Classical swine fever (CSF) virus in wild boars, are linked to the concepts of spread and invasion in a natural manner. They play a central role for the functioning of ecosystems and can interfere with the society's interests. Maintaining CSF, wild boar is demonstrated responsible for the majority of outbreaks in domestic pigs. Socially, large outbreaks of CSF in domestic pigs have a disastrous economic effect. Thus, the eradication of CSF virus in wild boar is a primary goal (EFSA, 2009).

EcoEpi research on CSF in wild boars aims to understand the disease course in the host population (Kramer-Schadt et al. 2007, 2009), to analyse host and pathogen interaction with the landscape (Fernandez et al. 2006) and to evaluate different control strategies like hunting or field vaccination. The approach combines process-oriented, individual- based and species habitat modelling. The modelling tools coupled virus epidemiology with wild boar population dynamics and dispersal in real geographical landscapes.

Using scenario analysis techniques, the model was challenged with alternative scientific reasoning regarding the persistence of the disease in wild boar populations (Kramer-Schadt et al. 2007). The results revealed the decisive impact of sufficient variability of diseases courses on the individual level (Kramer-Schadt et al. 2009) given the recognized size and density of recent wild boar populations. Linking the variable course of the infection in the individual host to modern changes in host ecology (large-scale planting for bio-energy production or milder winter climates) an interesting scenario pops up: Optimal feeding and limited seasonal mortality might guarantee a variety of individual conditions in the population ranging from wild boars in ideal constitution to those already weakly disposed. Hence, an outbreak likely provides relevant variability between individual hosts becoming infected, enhancing virus persistence on the population level, just like observed in today’s surveillance data.

Designed to be management-oriented, the research assisted for example in the societal discussion of wild boar restoration in Denmark through a risk analysis (Alban et al. 2005). The analysis delineated particular areas in Denmark which, although perfect for restoration purpose, were unsuitable from the society's perspective due to disproportionate risk for pig industry (Fernandez et al. 2006).

The pattern-oriented methodology (Grimm et al. 2005) guides further model development using large-scale historical data sets of CSF outbreaks in German wild boars. These data incorporate the effect of management from the point in time when oral vaccination was started. The investigation addresses the question of causality of observed impact of field vaccination (EFSA, 2009). Recent research activities (FP7, KBBE-2008-1-3-03, CSFV-goDIVA) are planned to support decisions on the future control strategy between public health interests, practicability and governance, or budgetary limitations.

EFSA (2009). Scientific report: Control and eradication of Classic Swine Fever in wild boar and Animal health safety of fresh meat derived from pigs vaccinated against Classic Swine Fever. Annex to The EFSA Journal 932:1-18 & 933:1-16
Kramer-Schadt S, Fernandez N, Eisinger D, Grimm V, Thulke HH (2009). Individual variation in infectiousness explains long-term disease persistence in wildlife populations. OIKOS 118:199-208.
Kramer-Schadt S, Fernandez N, Thulke HH (2007). Potential ecological and epidemiological factors affecting the persistence of classical swine fever in wild boar Sus scrofa populations. Mammal Review 37:1-20.
Fernandez N, Kramer-Schadt S, Thulke HH (2006). Viability and risk assessment in species restoration: planning reintroductions for the wild boar, a potential disease reservoir. Ecology and Society 11:6.
Alban L, Andersen MM, Asferg T, Boklund A, Fernandez N, Greiner M, Kramer-Schadt S, Stockmarr A, Thulke HH, Uttenthal Ă…, Ydesen B (2005). Classical swine fever and wild boar in Denmark: A risk analysis. Danish Institute for Food and Veterinary Research Project Report 118pp.
Grimm V, Revilla E, Berger U, Jeltsch F, Mooij WM, Railsback SF, Thulke HH, Weiner J, Wiegand T, DeAngelis DL (2005). Pattern-Oriented Modeling of Agent-Based Complex Systems: Lessons from Ecology. Science 310:987-991.

Supplementary Information