Detection of a virus enhancing factor in the spheroid, spindle, and virion of an entomopoxvirus

Spheroids, spindles, and virions of an entomopoxvirus (EPV) enhanced the infectivity of a nuclear polyhedrosis virus (NPV) when they were perorally administered to larvae of the armyworm, Pseudaletia separata. Spheroids and spindles at the same dose exhibited nearly the same enhancing activity. When the dose of spheroids or spindles was reduced 10 times, the median infectious dose of the NPV was increased approximately 100 times. An antiserum against an enhancing factor detected the homologous antigen in spheroids, spindles, and tissue-derived EPV virions but not in spheroid-derived virions.