- Classification: Fungi, Zygomycota, Chytridiomycetes, Incertae_sedis_, Incertae_sedis_, Olpidiaceae
- synonyme : Olpidium brassicae (Woronin) P.A. Dang., (1886)
- English name: Fungal vector virus

Olpidium virulentus, obligate parasitic fungus, is in fact a "non-cruciferous" strain of the species Olpidium brassicae sensu lato which was renamed following recent biological and molecular analyzes carried out in several species of Olpidium . It is certainly widespread worldwide and is not considered to be pathogenic for the majority of the plants on which it has been observed. It is reported on salad roots grown both in soil and in soil, and it is particularly feared in lettuce as a vector of two serious viruses: the ( lettuce large vein virus Mirafiori lettuce big vein virus , MLBBV ) and the agent ring necrosis lettuce ( lettuce ring necrosis agent , LRNA ).