sentences:  It was thought that DXV could have been pre-existent in "Drosophila" broods in a non-pathogenic form.Additionally, it was speculated that DXV might have originated as a contaminant from fetal calf serum in infection type studies because it was documented that endogenous bovine viruses were already in fetal calf serum.DXV is a Baltimore Class III naked (non-enveloped) virus.