Erns is a glycoprotein found on the surface of the BVDV viron. In addition to being a virion protein, a proportion of Erns is secreted from infected cells into the extracellular environment as a consequence of it lacking a typical transmembrane anchor domain.

The biological significance of secreted Erns has not been determined. However, Erns has two defined activities. First, Erns has an RNase activity that shows a strong preference for single-stranded RNA (ssRNA). Second, Erns glycoproteins of both BVDV and a closely related pestivirus, classical swine fever virus (CSFV), have been shown to bind to cell surface glycosylaminoglycans through residues located close to their C termini.