Foot-and-mouth disease is one of the most contagious viral animal diseases. It affects more than 70 domestic and wild species, in particular cattle, pigs, sheep and goats. Disease-free countries are not exempt, as has been shown by recent cases since January 2025 in Germany, Hungary and Slovakia. The disease has a major socio-economic impact on livestock sectors, both in areas where it is endemic and in the event of an incursion into a previously disease-free area. For more than 50 years, a complex question has been asked: in areas where the virus circulates, why is it able to persist in up to 50% of infected ruminants after their apparent recovery? ANSES's Laboratory for Animal Health sought to answer this question through FMDV_PersIstOmics, an international research project. This project revealed that one of the virus's proteins plays a key role in this persistence.