Epidemiological analysis of African swine fever in the European Union (September 2019 to August 2020)

Abstract

An update on the African swine fever (ASF) situation in the 10 affected Member States (MS) in the EU and in two neighbouring countries from the 1 September 2019 until the 31 August 2020 is provided. The dynamics of the proportions of PCR- and ELISA-positive samples since the first ASF detection in the country were provided and seasonal patterns were investigated. The impact of the ASF epidemic on the annual numbers of hunted wild boar in each affected MS was investigated. To evaluate differences in the extent of spread of ASF in the wild boar populations, the number of notifications that could be classified as secondary cases to a single source was calculated for each affected MS and compared for the earliest and latest year of the epidemic in the country. To evaluate possible risk factors for the occurrence of ASFV in wild boar or domestic pigs, a literature review was performed. Risk factors for the occurrence of ASF in wild boar in Romanian hunting grounds in 2019 were identified with a generalised linear model. The probability to find at least one PCR-confirmed ASF case in wild boar in a hunting ground in Romania was driven by environmental factors, wild boar abundance and the density of backyard pigs in the hunting ground area, while hunting-related variables were not retained in the final model. Finally, measures implemented in white zones (ASF-free zones that are geographically adjacent to an area where ASF is present in wild boar) to prevent further spread of ASF were analysed with a spatially, explicit stochastic individual-based model. To be effective, the wild boar population in the white zone would need to be drastically reduced before ASF arrives at the zone and it must be wide enough. To achieve the necessary pre-emptive culling targets of wild boar in the white zone, at the start of the establishment, the white zone should be placed sufficiently far from the affected area, considering the speed of the natural spread of the disease. This spread is faster in denser wild boar populations. After a focal ASF introduction, the white zone is always close to the infection hence pre-emptive culling measures in the white zone must be completed in short term, i.e. in a few months.

Keywords: African swine fever; domestic pigs; epidemiology; management; prevention; risk factor; seasonality; white zones; wild boar.

Figure 1

Total numbers of cases in wild boar and outbreaks in pigs per year reported to Animal Disease Notification System from 1/1/2014 to 31/8/2020, per year

Figure 2

Heat map displaying the pairwise correlation between potential risk factors, where blue and red shades indicate negative and positive pairwise correlations

Figure 3

Schematic representation to build the DAG network and calculate the number of nodes connected to each source of infections

Figure 4

Reported ASF genotype II outbreaks in domestic pigs since the first introduction in the EU, Ukraine and Serbia until 31 August 2020

Figure 5

Reported ASF genotype II cases and outbreaks in pigs and wild boar during the reporting period (1 September until 31 August 2020) in the EU, Ukraine and Serbia

Figure 6

Reported ASF cases in wild boar since the first introduction in Belgium up to 31 August 2020

Figure 7

Regulated zones in Belgium, May 2020. Blue line: border of Part I, surrounding zone II and in which no cases of ASF has been recorded; Pink line: border of Part II in which ASF has only been detected in wild boar

Figure 8

ASF outbreaks reported to the Animal Disease Notification System in domestic pigs since the first introduction in Bulgaria up to 31 August 2020

Figure 9

ASF cases reported to the Animal Disease Notification System in wild boar since the first introduction in Bulgaria up to 31 August 2020

Figure 10

ASF outbreaks reported to the Animal Disease Notification System in domestic pigs since the first introduction in Estonia up to 31 August 2020

Figure 11

ASF cases reported to the Animal Disease Notification System in wild boar since the first introduction in Estonia up to 31 August 2020

Figure 12

ASF outbreaks reported to the Animal Disease Notification System in domestic pigs since the first introduction in Greece up to 31 August 2020

Figure 13

ASF cases reported to the Animal Disease Notification System in wild boar since the first introduction in Hungary up to 31 August 2020

Figure 14

ASF outbreaks reported to the Animal Disease Notification System in domestic pigs since the first introduction in Lithuania up to 31 August 2020

Figure 15

ASF cases reported to the Animal Disease Notification System in wild boar since the first introduction in Lithuania up to 31 August 2020

Figure 16

ASF outbreaks reported to the Animal Disease Notification System in domestic pigs since the first introduction in Latvia up to 31 August 2020

Figure 17

ASF cases reported to the Animal Disease Notification System in wild boar since the first introduction in Latvia up to 31 August 2020

Figure 18

ASF outbreaks reported to the Animal Disease Notification System in domestic pigs since the first introduction in Poland up to 31 August 2020

Figure 19

ASF cases reported to the Animal Disease Notification System in wild boar since the first introduction in Poland up to 31 August 2020

Figure 20

ASF‐affected area in western Poland and the confirmed cases (red dots). The areas of forests have been indicated in green. The region marked with red indicates the estimated buffer zone (10 km) from the confirmed ASF cases

Figure 21

ASF outbreaks reported to the Animal Disease Notification System in domestic pigs since the first introduction in Romania up to 31 August 2020

Figure 22

ASF cases reported to the Animal Disease Notification System in wild boar since the first introduction in Romania up to 31 August 2020

Figure 23

ASF notifications in domestic pigs and wild boar from September 2019 to August 2020 in Russia up to 31 August 2020

Figure 24

Number of ASF outbreaks in domestic pigs and wild boar between 2007 and 2020 in Russia

Figure 25

Distribution of ASF affected pig holdings by size (A) and holding types (B)

Figure 26

ASF outbreaks reported to the Animal Disease Notification System in domestic pigs since the first introduction in Slovakia up to 31 August 2020

Figure 27

ASF cases reported to the Animal Disease Notification System in wild boar since the first introduction in Slovakia up to 31 August 2020

Figure 28

ASF outbreaks reported to the Animal Disease Notification System in domestic pigs since the first introduction in Serbia up to 31 August 2020

Figure 29

ASF cases reported to the Animal Disease Notification System in wild boar since the first introduction in Serbia up to 31 August 2020

Figure 30

Proportion of ASFV‐positive samples (only by PCR) over the tested samples from wild boar found dead (A) and from hunted wild boar (B) in the ASF‐affected areas of Belgium (1 January 2016–31 August 2020)

Figure 31

Proportion of ASFV‐positive samples (by Ab ELISA and PCR) over the tested samples from all wild boar found dead (A) and from hunted wild boar (B) in the ASF‐affected areas of Czechia (1 January 2016–31 August 2020)

Figure 32

Proportion of ASFV‐positive samples (by Ab ELISA and PCR) over the tested samples from all wild boar found dead (A) and from hunted wild boar (B) in the ASF‐affected areas of Estonia (1 January 2016–31 August 2020)

Figure 33

Proportion of ASFV‐positive samples (only by PCR) over the tested samples from all wild boar found dead (A) and from hunted wild boar (B) in the ASF‐affected areas of Hungary (1 January 2016–31 August 2020)

Figure 34

Proportion of ASFV‐positive samples (by Ab ELISA and PCR) over the tested samples from all wild boar found dead (A) and from hunted wild boar (B) in the ASF‐affected areas of Lithuania (1 January 2016–31 August 2020)

Figure 35

Proportion of ASFV‐positive samples (by Ab ELISA and PCR) over the tested samples from all wild boar found dead (A) and from hunted wild boar (B) in the ASF‐affected areas of Latvia (1 January 2016–31 August 2020)

Figure 36

Proportion of ASFV‐positive samples (by Ab ELISA and PCR) over the tested samples from all wild boar found dead (A) and from hunted wild boar (B) in the ASF‐affected areas of Poland (1 January 2016–31 August 2020)

Figure 37

Proportion of ASFV‐positive samples (by Ab ELISA and PCR) over the tested samples from all wild boar found dead (A) and from hunted wild boar (B) in the ASF‐affected areas of Romania (1 January 2016–31 December 2019)

Figure 38

Proportion of ASFV‐positive samples (by Ab ELISA and PCR) over the tested samples from all domestic pigs in the ASF‐affected areas of Lithuania (1 January 2016–31 August 2020) (A), Poland (1 January 2016–31 August 2020) (B) and Romania (1 January 2016–31 December 2019) (c) (a)

Figure 39

Proportion of domestic pigs testing positive to ASF (PCR) in Lithuania (A), Poland (B) and Romania (C) by calendar month, date and region

Figure 40

Proportion of wild boar testing positive to ASF (PCR) in Belgium by calendar month, date and region for animals found dead (left) or hunted (right)

Figure 41

Proportion of wild boar testing positive to ASF (PCR) in Czechia by calendar month, date and region for animals found dead (left) or hunted (right)

Figure 42

Proportion of wild boar testing positive to ASF (PCR) in Estonia by calendar month, date and region for animals found dead (left) or hunted (right)

Figure 43

Proportion of wild boar testing positive to ASF (PCR) in Hungary by calendar month, date and region for animals found dead (left) or hunted (right)

Figure 44

Proportion of wild boar testing positive to ASF (PCR) in Lithuania by calendar month, date and region for animals found dead (left) or hunted (right)

Figure 45

Proportion of wild boar testing positive to ASF (PCR) in Latvia by calendar month, date and region for animals found dead (left) or hunted (right)

Figure 46

Proportion of wild boar testing positive to ASF (PCR) in Poland by calendar month, date and region for animals found dead (left) or hunted (right)

Figure 47

Proportion of wild boar testing positive to ASF (PCR) in Romania by calendar month, date and region for animals found dead (left) or hunted (right)

Figure 48

Proportion of wild boar testing positive to ASF (PCR) in Slovakia by calendar month, for animals found dead (left) or hunted (right)

Figure 49

Annual number of hunted wild boar in the ASF‐affected the Baltic States in the last two decades

Figure 50

Annual number of hunted wild boar in several EU Member States affected by ASF in the last decades

Figure 51

Frequencies of potential secondary cases caused by a single source case in Estonia, obtained by bootstrapping

Figure 52

The frequencies of potential secondary cases caused by a single source case in Bulgaria, obtained by bootstrapping

Figure 53

Average probability to get a PCR‐positive test result in samples from domestic pig in the different countries of Romania, from 2017 to 2019

Figure 54

Proportion of ASF PCR positive reported per hunting ground (HG) region in 2019 in Romania

Figure 55. White zone in France

Figure 56. White zone in Luxembourg

Figure 57. Fence bordering white zone in Luxembourg

Figure 58. White zone in Estonia

Figure 59. Latvian white zone

Figure 60. White zone in Czechia

Figure 61. Fence bordering white zone in Czechia

Figure 62

Simulation area including the white zone in Estonia. Grid cells represent wild boar group habitats. The lighter the shading of a cell the better the wild boar habitat


1. Grey squares: ASF‐infected area;

2. Red squares: white zone;

3. Blue squares: ASF‐free area in front of white zone;

4. Black squares: represent virtually blocked cells preventing ASF infection from bypassing the WZ to the north or south;

5. Yellow dots: human‐mediated spread events before establishment of the WZ.

Figure 63

Heat map of local ASF occurrence inside and adjacent to the white zone in Estonia

Figure 64

Time interval from establishment of the white zone in Estonia until the entry of ASF into the WZ. Data are shown for three different median starting densities 1.2., 1.5 and 2.3 wild boar/km² (density scale 1.5, 2.0 and 3.0; x‐axis). Top row values represent percentage of runs in which the white zone did fail to halt the spread of ASF

Figure 65

A–B. Simulation area representing the white zone in Latvia (A) and snapshot of the simulation at the moment of establishment of the white zone in Latvia (B)

Figure 66

A–C. Heat map of ASF occurrence inside and adjacent to the white zone in Latvia

Figure 67

Time interval from establishment of the white zone in Latvia till entry of ASF into the white zone area. Data are shown for alternative management scenarios (x‐axis). Top row values represent percentage of runs in which the managed white zone did fail to halt the spread of ASF

Figure 68

A–B. Heat map of ASF occurrence inside and adjacent to the white zone in Latvia. As Figure 66C (failure rate 94%) but simulation additionally includes carcass removal inside the WZ assuming a detection efficiency of 20% (A; failure rate 34%) and 2% (B; failure rate 90%)

Figure 69

Simulation area representing the layout of the white zone in Czechia (A), the historic organisation of areas (B) and a snapshot of the simulation at the moment of establishment of the white zone in Czechia (C)

Figure 70

Heat map of ASF occurrence inside and adjacent to the WZ‐CZ


1. Note to these figure: The disease incursion in Czechia's white zone is simulated to evaluate the measures applied in the zone. In the reality, there was no notified introduction of ASF in the white zone in Czechia
Colour scale: proportion of simulations runs in which the square cell became infected, ranging from red (proportion of the simulation runs for which the cell became infected = 1) to dark blue (proportion of the simulation runs for which the cell became infected = 0).

Figure 71

Simulation area representing the white zone in France (red hashed) and the cumulated ASF notification in BE wild boar (A) and the structure of the underlying wild boar habitat patches (B)

Figure 72

A–B. Development of the population size inside the fenced part of the WZ‐FR (intense hashed red in Figure 71) according to MS data (A) and model output (B)

Figure 73

A–D. Heat map of ASF occurrence inside and adjacent to the WZ‐FR. Failure rate (A) 22%, (B) 46%, (C) 60% and (D) 91%


1. Note to these figures: The disease incursion in the French white zone is simulated to evaluate the measures applied in the zone. In the reality, there was no introduction of ASF in France.