Herpesviruses are ubiquitous and continue to be responsible for significant morbidity and mortality in the human population. In addition, with the increasing incidence of syndromes in which immunosuppression represents a base, there is a corresponding increase in numbers of clinically significant herpesvirus infections. The long-term objective of this proposal is a neurovirulence, and neuroinvasiveness--knowledge that is fundamental to design of methods for control of these agents. Although the primary interest is in Herpes simplex type I (HSV-I), studies presented. With respect to HSV-I, a molecular and functional analysis of the latent phase transcription units facilitate viral reactivation, and a definition of other viral genes functioning in reactivation is also sought. Comparative studies will be concerned with HSV-II and PrV. Investigations of CMV (initially murine, and then human) will focus on identifying latently. Infected cells and defining viral transcription in these cells. These aims will be accomplished in experimental animals (principally mice and rabbits), and will involve the application of contemporary molecular biological approaches coupled with more traditional virologic and experimental pathologic methods. In studies of HSV neuroinvasiveness and latency, animals will be inoculated on rear footpads, and lumbosacral spinal ganglia will be the organs of particular interest. Viral reactivation studies will employ the rabbit cornea-epinephrine model. Cytomegalovirus will be studied principally in murine spleens after parenteral inoculation. When a foundation has been established in the model, investigations of appropriate human autopsy-derived material will follow. Of particular importance with respect to methods will be those concerned with 1) the generation and application of HSV-1 recombinants with various inserts and deletions in the genomic region encoding the latency associated transcription unit, 2) biological analysis of viral genes involved in neuroinvasiveness and neurovirulence, and 3) technologies for development of a more readily investigated "reactivation system" than the rabbit cornea model presently serving as the base for study. In all systems, continued application of in situ hybridization technologies to identify involved cells and viral transcripts will be employed.