Abstract: The invention consists of a non-naturally occurring nucleic acid molecule capable of blocking or interfering with a replicative intermediate of a virus, a virusoid, or a viroid. The nucleic acid molecule may contain a ribozyme or a plurality of ribozymes. Alternatively, the nucleic acid molecule may be an antisense nucleic acid molecule. The ribozyme may be a hairpin ribozyme, a hammerhead ribozyme, an RNAase P ribozyme, a minizyme, or other catalytic RNA molecule. The virus may be an animal, a mammalian, a plant, a fungal, a protozoan, a yeast, a bacterial virus, or a human virus. The nucleic acid molecule may be expressed in the cell or it may be preformed and administered ex vivo. The present invention contemplates methods of controlling infection of a pathogenic infectious agent in a plant or animal.