Updated on 13/01/2021
Animal health, Animal diseases, African swine fever
African swine fever (ASF) is a viral haemorrhagic disease that affects domestic pigs and wild boar but cannot be transmitted to humans. It is now present in certain European and Asian countries and poses a threat to the professional sectors concerned. ANSES has been working to improve detection of the virus, and providing technical and scientific support to enable the authorities to implement effective management measures to prevent the introduction and spread of the disease in France.
What is African swine fever? Where did it come from?
African Swine Fever (ASF) is a viral disease that causes an often fatal haemorrhagic syndrome in its acute forms, only in domestic and wild pigs. It is contagious in European swine but inapparent in wild African swine (bushpigs and warthogs), and is not transmissible to humans. The causal agent of ASF is a DNA virus belonging to the family Asfarviridae. This disease causes major economic losses due to its high mortality rate and the trade restrictions imposed on affected countries.
ASF is classified as a Category 1 health hazard in France.
This disease has been around for at least a century in wild swine from sub-Saharan Africa (bushpigs, warthogs and other forest hogs), but they do not develop symptoms. First described in Kenya in 1921, ASF spread in Africa from pig to pig and through soft tick bites, to become endemic in sub-Saharan Africa.
Its first forays outside Africa date back to the 1960s, in line with the development of international trade. The American and European outbreaks were eradicated fairly rapidly, except in the Iberian Peninsula, which had to wait until 1995, and in Sardinia, where ASF has become enzootic since its introduction in 1978. No further cases were reported until 2007, with the exception of one in Portugal in 1999 – due to a previously decontaminated farm being recontaminated by soft ticks of the species Ornithodoros erraticus that had remained infected with the virus – and Sardinia.
In 2007, however, the European continent was affected once again, with an initial detection of outbreaks in pig farms in Georgia. Contaminated cuts of pork meat unloaded from a ship were thought to be behind the introduction of the virus to the continent. In 2008, the disease gradually colonised Eurasia (Armenia, Azerbaijan, Southern Russia), affecting both wildlife and domestic animals. It continued to advance westwards, either spreading locally in small, poorly controlled herds fed on swill or kitchen waste, or jumping several thousand kilometres, most likely due to the transport of contaminated meat, carcasses or delicatessen meat ending up in kitchen waste and fed to pigs (a tradition that continues in these countries, but that is formally prohibited in France and the rest of the European Union). The epidemic eventually reached Belarus.
In 2014, ASF returned to the European Union, first in Poland and the Baltic States, where it has since become enzootic in wild boar, then in Moldova (2016), Romania and the Czech Republic (2017), Hungary and Belgium (2018), and Germany (2020). In addition, since August 2018, the Asian continent has been widely affected: China, then Mongolia, Taiwan and Vietnam, the Philippines (in 2019) and India (in 2020).
ASF can be spread in all types of ways, and recent events in wildlife in Belgium, several thousand kilometres from the other infected European countries, and in Germany, a few kilometres from the Polish border (an ASF-infected area), illustrate the diversity in the ways it can spread.
The risk of spread has become global. France has been spared so far.
What is ANSES's role?
Through its Ploufragan-Plouzané-Niort Laboratory, which has been the National Reference Laboratory for ASF since 2001, and its Nancy Laboratory for Rabies and Wildlife, ANSES carries out research to:
- monitor the spread of the disease in neighbouring countries,
- diagnose ASF using reliable virological and serological detection tools,
- analyse the virus's pathogenesis mechanisms in pigs in order to develop a vaccine,
- study the vector and reservoir role of European soft ticks,
- study the potential spread of the virus within and between species, firstly through modelling, and secondly through knowledge of pig farming systems, and wild boar behaviour and population dynamics.
Following the detection of an outbreak of ASF in Belgium, just a few kilometres from the French border, ANSES set up an emergency collective expert appraisal group, bringing together virologists, epidemiologists and biologists, some of whom are from the above-mentioned laboratories.
To date, the expert group has issued some fifteen scientific opinions on the risks of introduction of ASF in France, on the safety measures to be taken in France to prevent the risk of spread of the disease in our country, on the risk of spread of the ASF virus by different media, in farming or in the environment, and on the potential role of arthropods in virus transmission.
ASF in 11 questions:
No, African swine fever cannot be transmitted to humans.
In Europe, African swine fever only affects:
• domestic pigs
• wild boar
In Africa, as part of the sylvatic cycle, the virus circulates between soft ticks living in burrows and young warthogs, which develop viraemia but survive. The virus is then no longer detected in adults. It is likely that the warthog immune system long ago learned to control infection through virus/host adaptation, but the determinants of these mechanisms are still unknown.
A healthy animal can be contaminated:
- by contact with an infected animal introduced into France, or with the carcass of an infected animal (the virus can survive for several months),
- by consumption of food contaminated with the virus. This could include meat and/or meat products from pigs or wild boar such as smoked or cured products, in which the virus can survive for more than two months.
This persistence of the virus in meat has generally been responsible for several ASF outbreaks occurring at various distances apart, due to animals being fed with untreated kitchen and table waste (swill, waste, foodstuffs, insufficiently heat-treated plasma). This practice is prohibited for farm animals in Europe. However, it is entirely possible that wild boar could come into contact with such waste and thus become contaminated.
- by the bite of ticks of the genus Ornithodoros: these soft ticks ingest the virus when feeding on the blood of infected animals and then transmit it by biting other susceptible animals. It should be noted that these soft ticks have not been identified in France, and that the ANSES opinion on the role of arthropods in the spread of ASF indicated that the probability of introduction and extension of soft ticks of the genus Ornithodoros sensu stricto in metropolitan France is considered to be almost nil (1 on a scale of 0 to 9).
- by contact with contaminated vehicles, people, or materials. Given the very high resistance of the virus in the outside environment, any soiled material (clothing, boots, needles, etc.) could favour indirect transmission of the virus.
The disease has three levels of virulence:
• the acute form
• the subacute form
• the chronic form
Symptoms and lesions are similar to those described for classical swine fever (hog cholera):
• haematological disorders,
• skin redness,
• impaired coordination,
Death occurs in 4 to 13 days with a mortality rate of 100% in the acute form, or in 30 to 40 days with lower mortality in the subacute form. The disease can progress for several months in the chronic form. Only laboratory tests (virological and/or serological) can provide a reliable diagnosis and differentiate ASF from classical swine fever.
There is currently no treatment or vaccine for this disease. The virus responsible for ASF, the only member of the viral family Asfarviridae, is a very large and complex DNA virus. It infects the cells of the monocyte-macrophage lineage, and diverts the immune response in its favour. Its genome was only fully sequenced in recent years and not all the genes involved in virulence or protection have yet been identified, delaying the development of a reliable and effective vaccine.
If you suspect a case of ASF, contact your veterinarian immediately.
From 2014, ASF made inroads in the European Union, firstly in Poland and the Baltic States (Estonia, Lithuania, Latvia), where it has become enzootic in wild boar. The infection has since then spread to new countries: Moldova (2016), Romania (2017), Czech Republic (2017) and more recently Hungary (April 2018), Belgium (September 2018) and Germany (September 2020).
The Asian continent is also affected, with China in August 2018, Mongolia in January 2019, Taiwan and Vietnam in February 2019. The risk of spread has become global.
ASF causes major economic losses in the pork production sector due to its high mortality rate and the trade restrictions imposed on affected countries. For example, China, the world's largest pig producer, has lost more than 6.7 million pigs since the outbreak began in August 2018.
In France, ASF is classified as a Category 1 health hazard.
In September 2018, the Ministry of Agriculture put in place an action plan on Organisation for the prevention, surveillance and control of African swine fever.
To prevent the risk of introduction of the virus in France, awareness-raising measures have been taken (posters, radio spots, etc.). They are intended for the general public as well as for more targeted stakeholders: farmers, transport companies, veterinarians, technicians, hunters, workers from the affected countries.
In order to monitor the spread of the virus, for example, they are being asked:
- For domestic animals: to notify any clinical signs, lesions or excess mortality for which the presence of swine fever cannot be excluded;
- For wildlife: to report any wild boar mortality to the SAGIR network.
Lastly, in order to combat ASF, "white depopulation areas", located near the regulated areas where ASF cases are rife in Belgium, have been fenced off and animals are being culled by hunters, the French Biodiversity Agency (OFB) and the National Forestry Office (ONF).
- Before buying feed, bedding or pigs, make sure they come from reliable farms that have taken the necessary measures to protect their operations from the virus,
- Do not let your pigs come into contact with wild boar or pigs from other farms,
- Never feed kitchen waste to pigs,
- Avoid free-range farming in areas affected by ASF.
During a hunt:
- Do not leave wild boar viscera in the woods,
- Do not leave food or rubbish in areas where wild boar may be present.
After a hunt:
- Stay away from domestic ports,
- Wash your hands with soap and water,
- Clean and disinfect your boots, equipment and vehicles used (including wheels and vehicle interior).
If you have been hunting in an infected country, you are asked to avoid:
- Bringing hunting trophies back to France,
- Importing wild boar from infected countries.
Members of the public and truck drivers:
- Avoid bringing meat or delicatessen meat from infected countries back to France,
- In motorway rest areas, during walks in the forest, etc. be sure to throw your food waste in the bin.
In all cases: if you find a dead wild boar, even if the area is unaffected by ASF, contact the official veterinary authorities without delay via the SAGIR network.
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