Description of the disease and ANSES's related activities
Published on 30/04/2019
Animal health, Animal diseases, African swine fever
African swine fever (ASF) is a haemorrhagic viral disease that affects only domestic pigs and wild boars and is not contagious to humans. Its presence in certain European countries represents a threat to the affected professional sectors. ANSES conducts work to improve detection of the virus and to supply technical and scientific support to authorities for the implementation of effective management measures to prevent the disease from being introduced into France.
What is African swine fever?
African swine fever is a viral disease that affects only domestic and wild suids (pigs, hogs and boars) and causes a haemorrhagic syndrome that is often fatal in its acute forms. It is contagious in European suids but inapparent in African wild suids (warthogs [Phacochoerus] , bush and river pigs [Potamochoerus].
The pathogen responsible for African swine fever is a DNA virus of the Asfarviridae family.
This disease, which is not transmissible to humans, causes major economic losses due to its high mortality rate and the trade restrictions imposed on affected countries. African swine fever (ASF) is classified as a category 1 health hazard in France.
How is the disease transmitted?
The disease is transmitted by direct contact from a sick animal to a healthy animal or by contact of a healthy animal with food or an environment contaminated with the virus. Transmission is also possible through ticks of the genus Ornithodoros that ingest the virus by feeding on the blood of infected animals, then transmit it by biting other susceptible animals.
This virus is highly resistant to secretions, excretions and products from contaminated pigs, including smoking and curing products in which it can survive for more than two months.
Blood is an essential means of transmission in farms (needles, etc.). Given the very high resistance of the virus in the external environment, any contaminated material can promote indirect transmission (material, humans, boots, vehicles). The persistence of the virus in meat is generally the reason for remote contamination through the distribution of untreated kitchen waste material to animals (swill, rubbish, foodstuffs, plasmas having undergone insufficient heat treatment).
What are the symptoms and how to should the disease be diagnosed?
There are 3 levels of virulence: acute, subacute and chronic. The symptoms and lesions are similar to those described for classical swine fever: hyperthermia, haematological disorders, skin redness, anorexia, lethargy, coordination disorders, vomiting and diarrhoea.
In the acute form of the disease, 100% of pig deaths occur in 4 to 13 days, while with the subacute form the percentage of mortalities is lower and deaths occur within 30 to 40 days. In the chronic form, the disease can progress over several months.
Only laboratory tests (virological and/or serological) can provide a reliable diagnosis and differentiate between ASF and classical swine fever.
Originally described in Africa (Kenya, 1921), ASF is endemic in sub-Saharan Africa. Its first incursions outside Africa date back to the 1960s, in connection with the development of international trade. American outbreaks of the disease were eradicated fairly quickly, as were the European ones, except in the Iberian Peninsula where eradication was not achieved until 1995. Since then, no cases were reported until 2007, with the exception of one case in 1999 in Portugal which was due to recontamination of a previously decontaminated farm by soft ticks of the O. erraticus species remaining infected with the virus, and in Sardinia where ASF has become enzootic since its introduction in 1978.
In 2007, the European continent was again affected, with a first detection of outbreaks in pig farms in Georgia. The most likely explanation for this introduction of the virus into the Eurasian continent is that it arrived in a shipment of contaminated pig meat. In turn, Armenia, Azerbaijan and Russia were affected in 2008, including both wildlife and domestic animals. The infection spread to the Russian side of the Caucasus where its dissemination continued, mainly through human activity rather than by contact with wildlife, at an average rate of 350 km per year.
In 2014, ASF was introduced into the European Union, first in Poland and the Baltic States where it became enzootic in wild boars. The infection then reached new countries, including Moldova (2016), Romania (2017), the Czech Republic (2017) and more recently Hungary (April 2018) and Belgium (September 2018). The Asian continent has also been affected, with China in August 2018, Mongolia in January 2019, and Taiwan and Vietnam in February 2019. The risk of spread has become global.
How can ASF be fought and/or prevented?
No vaccine or antiviral control measures are available against ASF.
In September 2018, the Ministry of Agriculture set up an action plan entitled "Organisation for the prevention, surveillance and control of African swine fever".
ANSES and African swine fever
ANSES’s Ploufragan-Plouzané-Niort laboratory has been the National Reference Laboratory for this disease since 2001. Its work mainly focuses on three major themes, namely:
1) Validation of diagnostic tools adapted to the emergence of new strains of the disease. The goal here is to have reliable virological and serological detection tools that allow rapid diagnosis in the event of an outbreak.
2) Study of the virus’ mechanisms in pigs from a vaccine development perspective.
3) Work on the potential role of European Ornithodoros ticks as a reservoir for the virus.
In view of the disease’s progression throughout Europe, ANSES has made great efforts in order to diagnose any possible cases that might occur in France. As soon as the first cases appeared at the Franco-Belgian border, the Agency set up an Emergency collective expert assessment group (GECU) composed of virologists, epidemiologists and wildlife biologists. This group of experts provides support on the various questions concerning the management measures to be implemented in France, in coordination with the Belgian authorities, in order to prevent the epidemic from spreading within the country. More than ten scientific opinions on the subject have already been published.
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