Epidemiological investigations
Information on ASF cases in wild boar obtained by the local veterinary offices were entered into the German electronic animal disease information system (TSN, “Tierseuchennachrichtensystem”, German National Animal Disease Database) (Kroschewski et al., 2006). These data sets contain the date of suspicion and disease confirmation, the location (geographical coordinates), where the animal had been hunted or found dead, as well as the age and gender of each individual wild boar.
In addition, for most carcasses, photographs and a “checklist for wild boar carcasses found in the field” (https://www.fli.de/fileadmin/FLI/IfE/AG_Forensik_Wildschwein/Erhebungsbogen_Wildschwein.pdf) were made available for epidemiological investigations or retrieved by epidemiologists of the Friedrich-Loeffler-Institut (FLI). These data were used to estimate the minimum postmortem interval (PMI) as previously described (Probst, Gethmann, Amendt, et al., 2020; Probst, Gethmann, Hohmann, et al., 2020). The minimum PMI, i.e. the latest possible time point of death, was estimated based on morphological characteristics of the carcass, i.e. the decomposition stage of different body parts and accumulated decomposition (fresh, bloated, active decay, advanced decay, dry, and remains), mean temperature (at 2 m height) and rainfall in the previous weeks (retrieved from the nearest weather station in Coschen, Brandenburg; German Weather Service, Offenbach, Germany), type of microhabitat (dry/moist, direct sunlight/shade, etc.), entomological activity, characteristics of the decomposition island and evidence for vertebrate scavenging. Euclidian distances between the cases in Germany and those in Western Poland were calculated in km using the software package sp (Pebesma & Bivand, 2005) within the open source software R (http://www.r-project).
Data on ASF surveillance prior to the emergence of ASF in Germany were extracted from the CSF/ASF wild boar surveillance database of the European Union (https://surv-wildboar.eu) for the period from 1st November 2019 to 9th September 2020. This covered the whole period since cases of ASF had been reported from Western Poland. There was one individual data set for each wild boar, which contained the date and location, where the animal had been hunted or found dead. Furthermore, information was recorded on the circumstances of death for each animal, i.e. shot apparently healthy (active surveillance) or shot sick, found dead or involved in a traffic accident (passive surveillance).