The EcoEpi Lab provides an respository of material regarding modelling of infectious disease spread and control in European wild boar population (https://ecoepi.eu/ASFWB)
African Swine Fever
African swine fever (ASF) is a devastating transboundary virus infection of domestic and wild pigs. No vaccines or drugs are available to prevent or treat ASF infection. The epidemiological situation on ASF in the EU represents a threat to the pig sector and causes trade disruptions from affected areas. For more than a decade, ASF has spread throughout the Baltic countries, Poland, Romania and Germany. The infection was eradicated regionally in the Czech Republic and Begium applying standardised emergency measures comprising carcass search and removal, reactive landscape structuring using fencing and intensive depopulation measures inside fenced areas.
EcoEpi contributes since 2011 to the understanding of ASF spread in European wild boar populations using the individual-based landscape-level model SwiFCoIBM.
Main stepping stone:
In 2011 the spatio-temporal patterns of ASF notifications in Russian wild boar was explored in no indication of endemic constellation could be demonstrated (Siemen 2012; Lange et al. 2014). The insight was later confused with long-term presence of the infection in larger wild boar populations. While the long-term presence in e.g. an EU Member state's territory is due to the slow spatial spread and hence the time till the population is affected once, endemicity would require continued recirculation on the same location for several wild boar generations which is not yet demonstrated in Europe. Interestingly, territories that were fully affected by the infection e.g. Estonia, Lativia, recently recognise the only limited new case notification and the possible fade-out became again politically correct, so to say.
In 2014 the model was used to first investigations of the application of mobile barriers in the control of ASF spread at local scale (Lange & Thulke 2015). The model outcome implies that even with adequate failure of fences (break through chance or stochastic permeability) the multiple fencing and wait approach has compatible efficiency then subsequent depopulation of the same "demarkated" control zone. The vigilance of control extension was an important aspect of both strategies.
In 2015 the model analysis provided the ever first investigation of large-scale control measures in order to mitigate continental ASF spread within wild boar population (Lange 2015). At that time the conceptual understanding of the spatial dimensions was in the scope to create natural barriers by population culling or depopulation measures. The approach was further elaborated in 2017 to pride better understanding of the interaction of hunting and carcass removal under updated ASF knowledge (Thulke et al. 2017). Given the large areas to be included in preventive population reduction measures the approach was never applied with the adequate stringency and thus lead to continued expansion of the ASF affected area in the EU.
In 2017 we applied the model in counterfactual analysis of ADNS data and simulated ADNS records in order to elucidate the infection pathways of ASF in wild boar (within and between social groups and via carcasses of previously infected animals). The analysis suggested a very low chance of transmission through contaminated carcasses although infected animals should succumb where other wild boar potentially could access them i.e. ubiquous potential contacts but low effective transmission rate (Lange & Thulke 2017). Interestingly, the outcome of limited effective approaches to dead wild boar was subsequently reported by field experimentation that using camera trapping and pluged carcasses (Probst et al 2017).
In 2017 we addressed the hypothesis about sero-prevalnce levels that wre deemed to raise indicating a virtue attenuation of the ASF virus. Using an multi-strain model apporach in an individual-based wild boar population with local transmission scale it was show that sero-prevlence in the population raises as in the observational data without any attenuation. Moreover, an spontaneously emerging attenuated strain would be outcompeted as long as the territory/the population is not yet completely affected by the epidemic spread.
In 2018 the implementation of emergency measures in the wild boar management zones following a focal ASF introduction was evaluated using the SwiFCoIBM (Lange et al. 2018). As a sole control strategy, intensive hunting around the buffer area might not always be sufficient to eradicate ASF. However, the probability of eradication success is increased after adding quick and safe carcass removal. A wider buffer area leads to a higher success probability; however it implies a larger intensive hunting area and the need for more animals to be hunted. If carcass removal and intensive hunting are effectively implemented, fencing is more useful for delineating zones, rather than adding substantially to control efficacy.The detailed investigation could not confirm the pragmatic that in the affected inner area population measures should be delayed to leave the effective reduction to he disease. The concept is vulnerable due to the continued high-level circulation of the infection. The earlier carcasses are cleared and live wild boars destroyed inside the fenced affected part the faster the success of the measures could be achieved in the model experiments even with semi-permeable fences. Unfortunately, in recent campaigns the removal of live animals from the affected areas therefore is undervalued leading to more frequent breakouts and expansions of the affected zone.
In 2020 the model was reinstatiated in order to analyse the surveillance activities in the context of a potential fade-out/eradication. The detailed model output allowed the performance testing of potential definitions of ASF freedom based on routine surveillance data (Lange et al. 2021a; exit strategy).
In 2021 a comparative assessment was undertaken comparing the historical layout and application protocol of preventively treated zones (Lange et al. 2021b; "White zones" or "Zone Blanche"). Beyond the approaches in fenced areas neighbourging ASF affected once (France & Czech Republic) this analysis also did cover zones that were targeted earlier in the EU actions by preemptive measures.
Classical Swine Fever (CSF)
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.
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).
References:
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 Å, 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.