Podgorski, T. | bioRxiv Science

bioRxiv2020

Social structure defines spatial transmission of African swine fever in wild boar

O_LISpatial spread of infectious disease is determined by spatial and social processes such as animal space use and family group structure. Yet, impacts of social processes on spatial spread remain poorly understood and estimates of spatial transmission kernels (STKs) often exclude social structure. Understanding impacts of social structure on STKs is important for obtaining robust inferences for policy decisions and optimizing response plans. C_LIO_LIWe fit spatially-explicit transmission models with different assumptions about contact structure to African swine fever virus (ASFv) surveillance data from Eastern Poland from 2014-2015 and evaluated how social structure affected inference of STKs and spatial spread. C_LIO_LIThe model with social structure provided better inference of spatial spread, predicted that [~]80% of transmission events occurred within family groups, and that transmission was weakly female-biased (other models predicted weakly male-biased transmission). In all models, most transmission events were within 1.5 km, with some rare events at longer distances. Effective reproductive numbers were between 1.1 and 2.5 (maximum values between 4 and 8). C_LIO_LISocial structure can modify spatial transmission dynamics. Accounting for this additional contact heterogeneity in spatial transmission models could provide more robust inferences of STKs for policy decisions, identify best control targets, and improve transparency in model uncertainty. C_LI

ecology↗

bioRxiv2019

Ecological drivers of African swine fever virus persistence in wild boar populations: insight for control

Environmental sources of infection can play a primary role in shaping epidemiological dynamics, however the relative impact of environmental transmission on host-pathogen systems is rarely estimated. We developed and fit a spatially-explicit model of African swine fever virus (ASFV) in wild boar to estimate what proportion of carcass-based transmission is contributing to the low-level persistence of ASFV in Eastern European wild boar. Our model was developed based on ecological insight and data from field studies of ASFV and wild boar in Eastern Poland. We predicted that carcass-based transmission would play a substantial role in persistence, especially in low-density host populations where contact rates are low. By fitting the model to outbreak data using Approximate Bayesian Computation, we inferred that between 53 to 66% of transmission events were carcass-based - i.e., transmitted through contact of a live host with a contaminated carcass. Model fitting and sensitivity analyses showed that the frequency of carcass-based transmission increased with decreasing host density, suggesting that management policies should emphasize the removal of carcasses and consider how reductions in host densities may drive carcass-based transmission. Sensitivity analyses also demonstrated that carcass-based transmission is necessary for the autonomous persistence of ASFV under realistic parameters. Autonomous persistence through direct transmission alone required high host densities; otherwise re-introduction of virus periodically was required for persistence when direct transmission probabilities were moderately high. We quantify the relative role of different persistence mechanisms for a low-prevalence disease using readily collected ecological data and viral surveillance data. Understanding how the frequency of different transmission mechanisms vary across host densities can help identify optimal management strategies across changing ecological conditions.

ecology↗