A complete genome based comparative evolutionary analysis of herpes simplex virus type 1 and varicella zoster virus

Herpes simplex virus type 1 (HSV-1) and varicella zoster virus (VZV) are closely related viruses causing lifelong infections. They are typically associated with mucocutaneous or skin lesions, but may also cause severe neurological or ophthalmic diseases, possible due to viral- and/or host-genetic factors. Although these viruses are well characterized, complete genome-based evolutionary studies have hitherto only been presented for VZV. Here, we present a complete genome based study on HSV-1, and compare the evolutionary characteristics of HSV-1 with those for VZV. We demonstrate that, in contrast to VZV for which only a few ancient recombination events have been suggested, all investigated HSV-1 genomes contain mosaic patterns of segments with different evolutionary origins. Thus, homologous recombination seems to occur extremely frequent for HSV-1. We conclude by proposing a timescale for HSV-1 evolution, and by discussing putative underlying reasons for why these otherwise biologically similar viruses have such striking evolutionary differences.