Orsay virus is a positive-sense single-stranded RNA virus that infects Caenorhabditis elegans nematode. It resembles nodaviruses (family Nodaviridae), but has yet to be formally classified. Orsay virus has a (+)ssRNA genome consisting of two segments, termed RNA1 and RNA2. The RNA1 segment encodes an RNA-dependent RNA polymerase (RdRP) of 982 amino acids. The RNA2 segment has two open reading frames (ORFs) that code for a capsid protein and a non-structural protein with unknown function. The virus is composed of two structural domains, a shell (S) and a protrusion (P) domain.