A mathematical model allows understanding the epidemiological dynamics of the African swine fever (ASF), in which the wild boar is a key actor, constituting an essential tool to control epidemic outbreaks and prevent health emergency situations.
The global health emergency caused by the pandemic disease due to the coronavirus COVID-19, known by science as severe acute respiratory syndrome coronavirus 2 or SARS-CoV-2, is highlighting the importance of understanding the epidemiological dynamics of infectious diseases to prevent the spread of epidemic outbreaks. This need is not limited to diseases that affect humans, but it is necessarily open to the world of animals, wildlife and biodiversity, which can play a key role in both disease transmission and prevention.
In this area, the African swine fever (ASF) is a deadly and highly contagious, severe viral disease that affects the domestic pig, the wild boar (Sus scrofa) that affects domestic pigs, wild boar (Sus scrofa) and African wild suids. The virus is spreading across Northern and Eastern Europe, where it constitutes a serious health threat, especially for countries that find in the pig farming sector a significant contributor for their economies. For example, if it were to arrive to Spain, the socioeconomic and environmental impacts of ASF would be dramatic, since it would mean the slaughter of pigs from affected farms and mortalities in wild boar populations that could exceed 90%.
The wild boar is a key actor in the epidemiology of the ASF and other infectious diseases that could contribute significantly to its spread.
Understanding the dynamics of infection, transmission and persistence of ASF is a priority for the health security of the European Union, since this information is essential to develop strategies to control its epidemic outbreaks and prevent the spread of the disease, avoiding situations of health emergency. In this context, the constant increase in the density of wild boar in Europe over the last decades represents an added challenge for the control of ASF, since wild boar is a key actor in the epidemiology of this and other infectious diseases that could contribute significantly to its spread.
A multi-disciplinary research team, made by scientists from the Maxwell Institute for Mathematical Sciences of the Heriot-Watt University (United Kingdom) and the Research Group in Health and Biotechnology (SaBio) of the Instituto de Investigación en Recursos Cinegéticos (IREC – CSIC, UCLM, JCCM), has developed a mathematical model of the wild boar-ASF system that considers the features involved in the processes that regulate the epidemiological dynamics of this disease, aimed to provide a key management tool to determine its behaviour and predict its spread and effects under different scenarios.
Implementing biosafety protocols to remove the carcasses of infected individuals is key for ASF eradication in wild boar populations.
Model results, which have been just published in the prestigious journal Scientific Reports, shows that environmental transmission is a key mechanism determining the severity of an infectious outbreak. Specifically, direct transmission between infected carcasses and infected live individuals and susceptible individuals, as well as transmission from individuals that survive the initial ASF infection, are key for the long-term persistence of the virus, making it difficult to eradicate and increasing the risk of spread to neighbouring populations.
The faster degradation of ASF-infected wild boar carcasses, mediated by a higher mean temperature and/or the presence of an abundant and well-preserved community of obligate scavengers (vultures), may reduce the severity of infectious outbreaks in some countries or geographic regions, including Spain. On contrary, management practices such as supplementary feeding lead to a more pronounced epidemic outbreak and persistence of the disease in the long-term.
The free service of enormous ecological and sanitary value provided by vultures may be key to control the ASF in wild boar populations.
The model, which allows assessing ASF control measures, suggest that a combination of wild boar population control through hunting and infected carcass removalis the most effective method to eradicate the virus, either through implementing biosafety protocols or favouring the free service of enormous ecological and sanitary value provided by vultures. Furthermore, the model shows that early implementation of these control measures would reduce infection levels whilst maintaining high wild boar densities (host population) and that, in some situations, it would prevent ASF from establishing in a population.
The scientific publication of this research is available at:
- O'Neill, X., White, A., Ruiz-Fons, F., Gortázar, C. 2020. Modelling the transmission and persistence of African swine fever in wild boar in contrasting European scenarios. Scientific Reports 10, 5895.