African swine fever has been present in the European Union since 2014. No treatment or vaccine is currently available once morest this disease, which infects wild boars and pigs. So far, no cases have been detected in France but the disease is circulating in Italy and Germany. It was also present in Belgium, where it was eradicated in October 2020. Scientists from the Anses laboratory in Ploufragan-Plouzané-Niort, and from the French office for biodiversity (OFB) have modeled the circulation of African swine fever in French wild boar populations. The study was published in the November 2022 issue of the journal Preventive Veterinary Medicine.
The fragmentation of the territory influences the spread of the disease
« We chose to do the modeling in two zones. The first is the territory close to the Belgian border, because when we started our study, African swine fever was circulating in this country. The second is the Pyrénées-Atlantiques, because free-range pig farms are important in this department, which can increase the risk of disease transmission between wild boars and pigs. explains Nicolas Rose, co-author of the study and head of the Epidemiology, Health and Well-Being Unit of the Ploufragan-Plouzané-Niort laboratory.
Both regions have different topographies : the area close to the Belgian border is very fragmented, with a territory cut by roads and towns. Conversely, the Pyrénées-Atlantiques are more homogeneous and have more continuous natural spaces. The natural fragmentation of the landscape restricts wild boar mobility and slows the spread of the disease. On the other hand, the simulated circulation of the disease lasts longer : 2.6 years on average in the Franco-Belgian region once morest 1.6 years in the Pyrénées-Atlantiques. However, the longer the disease circulates, the greater the risk of it being transmitted to domestic farms.
Stop hunting to prevent the spread of African swine fever
Another parameter that scientists have varied: the practice or not of recreational hunting. If hunting can reduce the number of infected individuals by reducing the susceptible population, it also results in disperse wild boar populations and therefore the disease. This is particularly notable in the Pyrénées-Atlantiques, where African swine fever would take an average of 300 days longer to disappear of the wild boar population if hunting were maintained. “ Hunting is normally suspended from the moment a case of African swine fever is detectedsays Nicolas Rose. The scenario where hunting would still be practiced is therefore rather theoretical, unless the contamination of wild boars goes unnoticed and therefore the disease is detected very late. Hence the importance of having a good detection capacity.
A method to eradicate the disease
Modeling has shown that the fragmentation of territories is decisive in slowing the spread of African swine fever. After an observation phase enabling the infected zones and the zones to be monitored to be clearly defined, the first measure to be adopted in the event of the detection of the disease would therefore be to placing barriers to reinforce habitat fragmentation. Another important measure to avoid contamination is the collection of carcasses. Once the disease is contained in an area and the number of contaminations becomes lower, the second step would consist in systematically slaughtering the wild boars present in the infected area. This method has eradicated African swine fever in Belgium and the Czech Republic.
ANSES scientists have also carried out work, not yet published, on the modeling of ASF transmission at the interface between wild populations and domestic pig farms. A third study is underway, in collaboration with the OFB, to model the possibilities of spreading African swine fever in the Franco-Italian zone. The challenge is to understand how the topography and in particular the altitude influences the movements of wild boars and thus to assess the speed and direction of spread of the disease in this area.
