Case description and epidemiological situation
The carcass of an adult female was found in a ditch between two
harvested maize fields at a dry location exposed to direct sunlight,
about 200 m off a country road in a community of the Spree-Neiße
district, Brandenburg, Germany ca. 6 km from the border with Poland
(Figure 1) by a person walking the dog. Foreleg bones of the largely
decomposed carcass were submitted by the responsible hunter for ASFV
testing and the carcass was buried on site on 7th September 2020. At the
time of detection, the hunter noticed large numbers of maggots on and
around the carcass. The mean temperature was 15°C (1st -7th September
2020) or 19°C (6th August – 7th September 2020), respectively. From 1st
August – 9th September 2020, the average rainfall was 6 mm. The carcass
was found in an advanced stage of decomposition and the minimum PMI was
estimated at two weeks. At that time, the adjacent region in Poland was
classified as a part I-region according to the implementing decision EU
2014/709, i.e. with a certain risk regarding ASF due to proximity of the
infection in the feral population (Figure 1).
Since the occurrence of ASF in wild boar in Western Poland, the risk of
introduction of ASF into Germany by migrating infected wild boar had
substantially increased. Preventive measures such as building a mobile
fence along the Polish border and increased surveillance in wild boar
and domestic pigs were introduced. The direct distance from the first
detected case in Brandenburg to the nearest ASF case in Poland, which
was confirmed within the preceding four weeks (13th August to
9th September 2020), was 33.9 km. The ASF case in Poland nearest to
Germany was detected at a distance of 10.4 km from the German border,
but south of the now affected area. Due to lack of information on the
surveillance intensity between the national border and the ASF focus in
Western Poland, direct evidence for a westward expansion of the infected
area in Western Poland is missing. Yet, it seems likely that the disease
has been introduced by migrating wild boar. (A new case, confirmed on
30th September 2020, located approx. 60 km north of the focus of the
first introduction into Germany, was also detected less than 2 km away
from the border with Poland). However, it cannot be excluded that human
activity (e.g. unsafe disposal of contaminated material) may have caused
the initial infection. ASFV remains infectious for a long time in pig
products, especially if blood is contained (Fischer, Hühr, Blome,
Conraths, & Probst, 2020; Kolbasov, Tsybanov, Malogolovkin, Gazaev, &
Mikolaxchuk, 2011; Mebus et al., 1997).
Wild boar and domestic pigs have been intensively monitored for ASF in
Germany in recent years. Especially in areas close to the
German-Polish-border, the efforts were intensified after the emergence
of the disease in Western Poland. Figure 2 shows the results of
surveillance within the affected region close to the German-Polish
border for the period from 1st November 2019 to 9th September 2020. A
total of 7.125 samples of wild boar (6.081 apparently healthy shot wild
boar, 312 wild boar found dead, 74 animals shot sick and 658 animals
killed in road traffic accidents) tested negative for ASF. Most wild
boar are examined during winter, when hunting is at its maximum.
Nevertheless, in the four months before the detection of the first case
of ASF in Germany, 50 wild boar found dead, 12 animals shot sick and 165
animals killed in road traffic accidents also tested negative for ASFV.
During the following days of intensified carcass search, four more
carcasses and a hunted wild boar with clinical signs were found 6 km
away from the first site. These carcasses were fresh with an estimated
minimum PMI of only a few days. Until 24th September 2020, a total of 32
cases of ASF were confirmed, of which nine were found close to the first
site and 23 in a small area further north (Figure 3). In both locations,
fresh and old carcasses of young and old wild boar were found (14
piglets, 6 subadults, 6 adult animals; the age of 6 animals could not be
assessed) (Table 1). At the place, where most carcasses were found, the
carcasses with the longest minimum PMI of 80 days were detected (Table
1).
PMI estimates were based on the macroscopically visible stage of decay,
the presence of insects and the microclimatic conditions at the sites.
However, when decomposition had reached an advanced stage and only
single skeletal remains were found, dating the PMI became difficult, in
particular when carcasses had obviously been used by large vertebrate
scavengers (red foxes and wolves are present in the area).
Based on the available data, the virus was probably introduced into
Germany in early July 2020 or even earlier. Since most of the detected
ASFV-infected wild boar died in September 2020 (Table 1), the situation
is still evolving.
From all these animals, dry blood swabs or bones (carcasses) or serum
(shot wild boar) were sent for laboratory diagnosis to the LLBB and for
confirmation to the NRL at the FLI.