Last year saw a five-fold increase in the number of outbreaks of African swine fever (ASF) in domestic pigs in the EU compared to 2022, according to the European Food Safety Authority (EFSA).
In new research, the EFSA said that 14 EU member states were affected by ASF in 2023, including Sweden and Croatia (which had not seen outbreaks previously, though their cases were in wild boar only), as well as Greece, which did not see any cases in 2022.
The number of outbreaks in domestic pigs reached a similar level as 2019, and was predominately driven by the introduction and subsequent spread of ASF in Croatia (1,124 outbreaks in 2023) and its resurgence in Romania (736 outbreaks), according to the EFSA.
These two countries accounted for 96% of all EU outbreaks in domestic pigs in 2023. In the rest of the EU, outbreaks among domestic pigs were more sporadic, with 30 in Poland, 16 in Italy, and less than 10 in each of the remaining affected countries.
96% of all outbreaks in the EU occurred on establishments with fewer than 100 pigs, while only six outbreaks occurred on premises with over 10,000 pigs, all of which were in Romania.
There was an apparent seasonal factor to outbreaks in domestic pigs, with 88% of outbreaks reported between July and October. This seasonal variation was more pronounced on smaller holdings.
In domestic pigs, 94% of outbreaks were detected through clinical suspicion, while 3% were detected by tracing animals from affected establishments, and a further 3% through testing of dead pigs.
No outbreaks were detected through the surveillance of healthy pigs at slaughter, before movement, or selected randomly.
ASF in wild boar
For wild boar, there was a 10% increase in the number of notified outbreaks in 2023 compared to 2022, but with considerable variation between countries. Poland saw the most outbreaks in wild boar, with 2,686 outbreaks.
A winter peak of wild boar cases was observed only in Poland, Slovakia and Hungary, and the situation with respect to wild boar improved in Hungary and Germany, as suggested by the decrease in the number of outbreaks, and in the proportion of positive samples from dead wild boar.
31% of wild boar carcasses found through passive surveillance (found dead or road killed) tested positive, which represented 7.9% of wild boar samples tested and 69% of ASF outbreaks in wild boar in the EU last year.
Only a small proportion – 0.4% – of hunted wild boar tested positive, although they accounted for 92% of tested wild boar samples, and represented 31% of the outbreaks in wild boar.
Despite the introduction of ASF into new countries and the increase in the number of outbreaks, the EFSA said that the size of restricted zones remained stable, due to highly clustered outbreaks in Croatia and the reduction of restricted zones in Poland, Slovakia and Bulgaria (for domestic pigs) and Hungary (for wild boar).
The total size of restricted zones in the EU for domestic pig outbreaks reduced by 4% last year, while the total size of restricted zones for wild boar outbreaks increased slightly.
The EFSA has recommended that passive surveillance, including the searching and testing of wild boar carcasses, be prioritised over active surveillance.
Passive surveillance, in particular noticing clinical signs of the disease, remains the main mode of detection for ASF in domestic pig establishments. Therefore, farmers and vets have a particularly important role to play, the authority said.
In October this year, the EFSA will deliver a scientific opinion revising the risk factors for the emergence, spread and persistence of the ASF virus in wild boar populations and domestic pigs.