Investigation of an outbreak of IBR in Saone-et-Loire using the algorithm Dijsktra

Numerous and unusual IBR epizootics were reported in the Summer 2008 in some areas of Saone-et-Loire (France). This led to investigations by the GDS (Animal Health Farmers' Organization) in the affected herds to understand how the virus had succeeded in contaminating various sections of those herds while they were grazing. Dijsktra's algorithm was used to analyze those observations. It is based on navigation softwares designed to find the shortest ways from one point to another in a graph-in this case, the infected parts of the herds - and their links - the various transmission routes, such as proximity in the grazing areas, animals being moved and interventions on the animals. The investigation recorded all the transmission routes reported by cattle-breeders concerning the infected parts of their herds. Moreover, a software - developed with Excel - explored all the transmission routes that could account for the epizootic. The explanation rate of the contaminated part is of 35% and can rise up to 58% if one admits that the BTV vaccination is a way of transmission. A simulation on the date of the beginning of the epizootic shows that the epizootic may have started previously than the BTV epizootic and that it is not linked to an eventual viral reactivation which would have been provoked by the BTV epizootic, which started on those areas during Summer 2008. The investigation and the method boundaries are being debated in the document.