Intrastrain variants of herpes simplex virus type 1 isolated from a neonate with fatal disseminated infection differ in the ICP34.5 gene, glycoprotein processing, and neuroinvasiveness

Two intrastrain variants of herpes simplex virus type 1 (HSV-1) were isolat ed from a newborn with fatal disseminated infection. A small-plaque-produci ng variant (SP7) was the predominant virus (>99%) in the brain, and a large -plaque-producing variant (LP5) was the predominant virus (>99%) in the lun g and gastrointestinal tract. EcoRI and BamHI restriction fragment patterns indicated that SP7 and LP5 are related strains. The large-plaque variants produced plaques similar in size to those produced by HSV-1 KOS. Unlike LP5 or KOS, SP7 was highly cell associated and processing of glycoprotein C an d glycoprotein D was limited to precursor forms in infected Vero cells. The large-plaque phenotype from KOS could be transferred into SP7 by cotransfe ction of plasmids containing the EK or JK EcoRI fragment or a 3-kb plasmid with the UL34.5 gene of HSV-1 KOS together with SP7 DNA. PCR analysis using primers from within the ICP34.5 gene indicated differences for SP7, LP5, a nd KOS. Sequencing data indicated two sets of deletions in the UL34.5 gene that distinguish SP7 from LP5. Both SP7 and LP5 variants were neurovirulent (lethal following intracranial inoculation of young BALB/c mice); however, the LP5 variant was much less able to cause lethal neuroinvasive disease ( footpad inoculation) whereas KOS caused no disease. Passage of SP7 selected for viruses (SLP-5 and SLP-10) which were attenuated for lethal neuroinvas ive disease, were not cell-associated, and differed in the UL34.5 gene. UL3 4.5 from SLP-5 or SLP-10 resembled that of KOS. These findings support a ro le for UL34.5 in promoting virus egress and for neuroinvasive disease.