ASF Sweden: A look back at a successful eradication
In late September 2024, the European Commission declared Sweden officially free from the African Swine Fever (ASF). In getting that status, Sweden joined a very small group of countries that managed to do the same. What went so well in Sweden?
There is so much data around the outbreak, it is best to look at the scientific data. Mid-2024, a large group of Swedish veterinary researchers reflected on the ASF outbreak in Sweden. The team published their review in a scientific publication in the peer-reviewed publication Transboundary and Emerging Diseases. Official data show that the outbreak 1 year before eventually affected 70 wild boar. It did not spread to commercial pig farms.
A quick look back to the ASF outbreaks in Sweden
The first case of ASF emerged in Sweden in September 2023. The carcass was found near Fagersta in Västmanland county, at 145 km from the capital Stockholm. Upon detection, the authorities took all measures according to European Union regulations. The Swedish authorities started a carcass search, including geo-localisation, removal, sampling, and destruction of found carcasses. The team defined a proper zonation to monitor and tackle the infection.
In the months after confirmation of the first case, the remains of 69 positive wild boar were found. 1 positive young wild boar was also found and shot. Even throughout 2024, various bones of positive animals were discovered. These however were all emaciated left-overs of wild boar that had died of the virus months ago – those did not constitute new infections.
Virus active between May and September 2023
In the publication, the researchers concluded that the infection must have been introduced between early May and late June 2023. Their data also indicated that the epidemic curve peaked between mid-August and mid-September 2023. The last death occurred in late September 2023.
To avoid further spread, all wild boar were shot in the restricted zones. Prof Karl Ståhl is state epizootiologist at the Swedish Veterinary Agency (SVA) and co-author of the scientific article. In correspondence with Pig Progress, he added, “During the entire operation 104 apparently healthy wild boar were shot in the restricted zone. However, given that we had the virus under control already by the end of September 2023, it is hard to say to what extent the culling of these wild boar contributed to the control. What we surely can say, however, is that they contributed to the surveillance and to our understanding of the situation.”
Municipal waste collection centre attracting wild boar
Soon after the discovery of the outbreak, it was already clear that its epicentre was a municipal waste collection centre without wild boar-proof fencing. In the scientific publication, the authors confirm that that place attracted many wild boar and contributed to the spread of the virus once it had been introduced to the population.
As for the route of infection of the virus, the authors reflected that disease introduction through natural wild boar movements was excluded and it was assumed that the long-distance translocation of the virus had occurred through human activities.
In the publication, the Swedish authors also refer to an online questionnaire to hunters in the infected zone. The results showed that the wild boar population in that area had increased in the last 10 years. However, with large variations and geographical heterogeneity in space use.
Success factors of getting ASF under control in Sweden
When asked for success factors, Dr Ståhl summed up 4 different reasons the Swedish authorities normally emphasise:
- The favourable conditions in the outbreak location (the outbreak took place in an area that is fairly northern – with a relatively low wild boar density, VtB);
- We were very well prepared and had high level of expertise within the country;
- The engagement of the local hunters;
- The collaborative effort where central, regional and local authorities collaborated very efficiently with the affected society as well as with the national hunting association and the local hunters. For this to be possible, I think the generally high level of trust between Swedish citizens and authorities is of key importance.
Wintery conditions did not play a role so much in controlling the outbreak, Dr Ståhl commented. He said, “By the time winter came to Fagersta, the outbreak was already over. No more cases and hardly any remaining wild boar in the core area.”
We have learnt several lessons that will improve our capacity to manage possible outbreaks in the future. One such thing is how important it is to have systems in place to plan and monitor search activities
The situation in 2025: surveillance
For Sweden, the situation early 2025 is “back to normal,” even though that does not mean that there is no vigilance. Dr Ståhl said, “All activities relating to managing the outbreak are over. But as in all parts of Sweden enhanced passive surveillance of wild boar found dead does continue.”
There are some key take-aways for Sweden which should be remembered, Dr Ståhl said. “We have learnt several lessons that will improve our capacity to manage possible outbreaks in the future. One such thing is how important it is to have systems in place to plan and monitor search activities. Disease surveillance in wildlife implies many challenges that we don’t have, when we manage diseases in production animals. These should be systems which are readily available for all people involved in the activities.
“In Sweden we had to develop such systems during the crisis (in a very fruitful collaboration between involved authorities and a private company providing hunting apps). This in the end worked very well – but of course it would have been preferable to have systems in place from day 1.
“Moreover, it is very clear that although being a very successful outbreak management operation from disease control perspective, implemented measures have had severe impact on the affected societies, on people’s daily lives and in many cases on their livelihood. This is something that needs to be taken into account.”
Additional research to effects of control measures
Additional research has also been initiated, he explained. Research grants will be used to improve the Swedes’ understanding of the impact of the different control measures implemented in the area. This is both from a disease control perspective and from an economic and societal and anthropological perspective.
Dr Ståhl concludes, “We are happy and proud, but also humble to the fact that the location of the outbreak gave us favourable conditions for a successful operation.”
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