Herpesviruses have been classified into three subfamilies on the basis of biological characteristics and genomic analysis. Members of the alphaherpesvirus subfamily are neurotropic, have a short replicative cycle, and, in general, have a broad host range. In addition, they encode a similar set of homologous genes arranged in similar order. Also, selected proteins of one alphaherpesvirus may functionally substitute for the homolog of another.

Human herpes simplex viruses 1 and 2 (HSV-1 and HSV-2), porcine pseudorabies virus (PRV), and bovine herpesvirus 1 (BHV-1) are representative members of the alphaherpesvirus subfamily and are the subject of this review. Natural diseases associated with infections by these viruses are restricted to specific hosts. However, these viruses can infect selected laboratory animals, such as rodents, and all have a relatively broad host range for cultured cells, at least for entry. The obvious inferences are that each of these viruses can use multiple cell surface receptors for entry or that each can recognize structural features of receptors conserved among human and animal species. The evidence summarized here shows that both inferences are correct. The usual manifestations of HSV disease are lesions on mucosal epithelium (oral or genital), skin, or cornea; latent infection of neurons in sensory ganglia; and perhaps recurrent lesions at the site of primary infection, due to reactivation of latent virus from the ganglia. Encephalitis can occur, albeit rarely in children or adults; newborn infants can suffer from severe disseminated disease. PRV and BHV-1 can cause similar manifestations of disease in pigs and cattle. Thus, important cel-