A composition for treatment of HSV-related pathologies including an expression vector for altering expression of a target sequence in an HSV-infected cell by production of single-stranded cDNA (ssDNA) in the cell in vivo suspended for topical application to an affected site in a suitable delivery vehicle. The expression vector is comprised of a cassette comprising a sequence of interest, an inverted tandem repeat, and a primer binding site 3' to the inverted tandem repeat, and a reverse transcriptase/RNAse H coding gene, and is transfected into the infected cells for inhibition of HSV replication. The resulting ssDNA binds to the target sequence to alter expression of the target sequence for such purposes as gene activation or inactivation using duplex or triplex binding of nucleic acids, site-directed mutagenesis, interruption of cellular function by binding to specific cellular proteins, or interfering with RNA splicing functions.