Impact of African Swine Fever Attenuated Virus Circulation in Wild Boar

Abstract

African swine fever (ASF) has been present in European wild boar since 2014. Control measures have reduced the incidence of the disease, but high virulent as well as attenuated ASF virus strains circulate. We depict the intraherd epidemiological parameters of low and highly virulent ASF in wild boar from experimental data and for the first time evaluate the impact of the circulation of attenuated strains through unique deterministic compartmental model simulations under several potential scenarios and hypotheses. With an estimated PCR infectious threshold of TPCR=36.4, we obtained several transmission parameters, like a Rx (experimental intraherd R0) of 4.5. We also estimate two novel epidemiological parameters, the infectious and resistance power, to denote the ability of animals to be transmissible and the reduction in infectiousness after consecutive varying virulence strains, respectively. The impact of ASF attenuated strains results in 4-17% of animals that can either remain in a carrier state or become susceptible again when exposed to highly virulent ASF for more than two years. The timing between exposures to viruses of different virulence also influences the percentage of animals that die or remain susceptible. The results of this study can be used in epidemiological modelling and bring insight into important risk situations that should be considered for surveillance and future potential ASF vaccination strategies in wild boar.

Keywords: African swine fever virus, wild boar, disease dynamics, ASF transmission, epidemic modeling, moderate or low virulence