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Title (Primary) Modelling advanced knowledge of African swine fever, resulting surveillance patterns at the population level and impact on reliable exit strategy definition
Author Lange, M.; Reichold, A.; Thulke, H.-H.;
Journal EFSA Supporting Publications
Year 2021
Department OESA;
Volume 18
Issue 3
Language englisch;
Keywords African Swine Fever, wild boar, individual-based, spatial-temporal simulation, exit strategy, white zone, control measures, hunting, carcass removal, fencing
Abstract African swine fever (ASF) is an infectious lethal disease affecting domestic pigs and wild boar. For more than a decade ASF infection by genotype IIhas been circulating in Eurasian wild boar populations. It can be transmitted via direct animal contact or contact with contaminated carcasses in the environment. After several years of virus circulation in European wild boar population ongoing disease surveillance suggests regional fade‐out of the infection. With this study an exit strategy based on routine surveillance procedures had to be informed and tested using an eco‐epidemiological spatially explicit individual‐based transmission model. The model simulations were performed on the geographical wild boar habitat map of Estonia and analysis referred to the administrative unit level of 2.500 km² on average (LAU1 units). The analysis addressed the temporal profile of virus‐ and sero‐positive animals in different age cohorts and the abundance of carcasses of animals succumbed to the disease in conjunction with regional virus‐fade out. Alternative scenarios were tested for their impact on the duration of virus circulation in a limited area. Finally, different criteria to decide on the final status ASF circulation in a region were tested for their reliability by mimicking routine volumes of passive and active surveillance. The temporal profiles confirm the limited chance of a direct demonstration of virus absence. Therefore, the exit decision requires monitoring periods of several months to years. In order to keep efforts down a two‐phase exit protocol does combine a longer phase with routine surveillance (the Screening phase) and a shorter (minimal) phase (the Confirmation phase) with increased surveillance (the maximum possible under field conditions). The two‐phase exit strategy facilitates trade‐off between invested surveillance efforts and total time to the final decision. Sensitivity of the exit decision is tested for uncertain aspects of ASF epidemiology and revealed performance decrease with increasing natural mortality, but improvement with increasing wild boar density and more distant translocations e.g. due to human activity. Survivors with extreme long‐term infectiousness (years), if they would exist, do render the tested exit decision as unreliable. However, there is no evidence in support of such an assumption. Virus attenuation in terms of increased proportion of survivors (up to 20% infected animals) and longer infectious periods (up to 4 weeks post infection) was congruent with the proposed exit strategy. The input to an exit decision by active surveillance i.e. testing of hunted animals, in particular for serology, was negligible.
ID 24360
Persistent UFZ Identifier
Lange, M., Reichold, A., Thulke, H.-H. (2021):
Modelling advanced knowledge of African swine fever, resulting surveillance patterns at the population level and impact on reliable exit strategy definition
EFSA Supporting Publications 18 (3), art. 6429E