Dynamics of the African Swine Fever Spread in Poland

Abstract

Introduction: African swine fever (ASF) is a lethal haemorrhagic disease of Suidae, present in Poland since 2014. The natural reservoir of ASF in Europe is the wild boar (Sus scrofa); however, human activity facilitates long-distance introductions of the disease. In ASF control it is important to identify areas at increased risk of infection. Such identification and estimation of the disease's progress and subsequent spread will help to identify the specific preventive action needs in given zones. Serving this purpose, this study is a spatial and statistical analysis of ASF spread through noted outbreak data.

Material and methods: The spatial-temporal analysis was conducted on the basis of data including the time and location of all ASF outbreaks both in wild boars and domestic pigs in Poland in 2014-2021.

Results: The analysis indicates possible routes and directions for further ASF spread in Poland, estimates the annual increase of the affected area (approx. 25,000 km² every year since 2017) and marks trends. The strong method-independent correlation between the year and the surface area affected by African swine fever indicated a near-linear generalised trend.

Conclusion: Given the growth trend, we can expect ASF to expand further into new territories of the country; however, it is important to realise that there is still a significant area to protect, because 60% of Poland remains ASF-free.

Keywords: ASF; Poland.; geostatistical analysis; spatial analysis; spread.

Fig. 1

Number of wild boars identified positive for African swine fever in Poland by year

Fig. 2

Number of ASF outbreaks detected in domestic pigs in Poland by year

Fig. 3

African swine fever (ASF) outbreaks in domestic pigs (blue) and wild boars (red), and restriction zones (as of 31/12/2021). Outbreaks in 2021 are shown in intense colours, and outbreaks in 2014–2020 in pastel colours. NUTS – nomenclature of territorial units for statistics

Fig. 4

The progress of African swine fever (ASF) in domestic pigs (blue) and wild boars (red) in the years 2014–2021. Outbreaks in a given year are shown in intense colours, and outbreaks in previous years in pastel colours. NUTS – nomenclature of territorial units for statistics

Fig. 5

Areas of African swine fever (ASF) occurrence in the years 2014–2021 shown as zones within 10 km of the outbreaks in domestic pigs and wild boars. NUTS – nomenclature of territorial units for statistics

Fig. 6

Annual areas of African swine fever (ASF) occurrence in domestic pigs and wild boars layered over a common map (oldest layer at the top). NUTS – nomenclature of territorial units for statistics

Fig. 7

The combined surface area of the 10-km radius buffer zones around the points where African swine fever occurred over the years in percentages of the surface area of Poland

Fig. 8

Scatterplots for Pearson’s correlation between the year and the surface area of the African swine fever occurrence zone: a) single-year area for outbreaks in domestic pigs and wild boars; b) multiple-year cumulative area for outbreaks in domestic pigs and wild boars; c) multiple-year cumulative area for outbreaks in wild boars only

Fig. 9

a) Ratio of the sum of African swine fever (ASF)-positive wild boars and ASF outbreaks in domestic pigs in a given year to the surface area of 10-km-radius buffer zones around the points of these events (units/km²) – green line. b) Ratio of the number of ASF-positive wild boars in a given year to the cumulative area (from the beginning of 2014) within a radius of 10 km from the sites of ASF outbreaks in wild boars (units/km²) – orange line

Fig. 10

Comparison of the African swine fever (ASF) occurrence areas (10-km zones around the outbreaks) between 2020 (green) and 2021 (beige). The common area is marked in grey

Fig. 11

50-km buffer from African swine fever (ASF) outbreaks in cumulative periods of 2014–2020 vs. 2014–2021. Pink shows the area for 2014–2020 (it is also the common part for both periods, i.e. for the buffer zones drawn at the ends of 2020 and 2021). Light brown represents the buffer surface area increase in 2021. NUTS – nomenclature of territorial units for statistics

Fig. 12

100-km buffer from African swine fever (ASF) outbreaks in cumulative periods of 2014–2020 vs. 2014–2021. Yellow shows the area for 2014–2020 (it is also the common part for both periods, i.e. for the buffer zones drawn at the ends of 2020 and 2021). Light green represents the buffer surface area increase in 2021. NUTS – nomenclature of territorial units for statistics