Abstract: The invention relates to methods of diagnosis or detection of Moissiacense virus, a novel orthobunyavirus causing human encephalitis, comprising determining the presence of at least one nucleic acid or protein of said virus or antibodies thereto, in a biological sample. The invention also relates to the various diagnostic agents derived from the viral nucleic acids or proteins, in articular nucleic acid primers and probes, antigens and antibodies, and their use for the diagnosis of Moissiacense virus infection and associated disease, in particular encephalitis. The invention further relates to antigens derived from the viral proteins as vaccine for the prevention of Moissiacense virus infection and associated disease, in particular encephalitis.