Abstract
To study the spread of African swine fever (ASF) within a pig unit and the impact of unit size on ASF spread, a simulation model was created. In the model, an animal can be in one of the following stages: susceptible, latent, subclinical, clinical, or recovered. Animals can be infectious during the subclinical stage and are fully infectious during the clinical stage. ASF virus (ASFV) infection through residues of dead animals in the slurries was also modeled in an exponentially fading-out pattern. Low and high transmission rates for ASFV were tested in the model. Robustness analysis was carried out in order to study the impact of uncertain parameters on model predictions. The results showed that the disease may fade out within the pig unit without a major outbreak. Furthermore, they showed that spread of ASFV is dependent on the infectiousness of subclinical animals and the residues of dead animals, the transmission rate of the virus, and importantly the unit size. Moreover, increasing the duration of the latent or the subclinical stages resulted in longer time to disease fade out. The proposed model is a simple and robust tool simulating the spread of ASFV within a pig house taking into account dynamics of ASFV spread and the unit size. The tool can be implemented in simulation models of ASFV spread between herds.
Highlights
African swine fever (ASF) is an infectious disease of pigs, caused by the ASF virus (ASFV), which is a DNA virus from the family Asfarviridae, genus Asfivirus [1]
The model considers the different stages of disease, which contributes to the transmission dynamics
Infection leads to the death of most of the affected animals [approximately 95% according to Gallardo et al [4]], and a limiting factor for disease spread, virus in blood, feces, and liquids from infected animals can persist in the slurry following biting by other pigs or from hemorrhagic diarrhea [4], and be a potential risk for disease spread
Summary
African swine fever (ASF) is an infectious disease of pigs, caused by the ASF virus (ASFV), which is a DNA virus from the family Asfarviridae, genus Asfivirus [1]. Infection with ASF is associated with a wide range of clinical symptoms from almost unapparent to severe clinical signs and death with mortality ranging from 3 to 100% [3]. In the recent outbreaks observed in Eastern and Central Europe, a high mortality has occurred, in which approximately 95% of the infected animals have died following the appearance of clinical symptoms [4]. The disease is endemic in Africa and is considered one of the biggest hurdles for the development of the pig sector in African countries, such as Uganda [5]. The disease has been persistent in Russia since 2008 [6], and since it has caused many cases and outbreaks in wild boar and domestic pigs in eastern European countries, such as Poland, Estonia, Latvia, and Lithuania [4, 7]. Oganesyan et al [10] pointed out the importance of anthropogenic factors
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