An Ecological Framework of the Human Virome Provides Classification of Current Knowledge and Identifies Areas of Forthcoming Discovery

Parker, Michael T.

Other examples of secondary symbiotic viruses are isolated, but numerous. In general, these viruses likely compete for receptors, cellular resources, or niches within hosts to confer protection. Hepatitis G Virus (HGV) is known to slow development of HIV infection to AIDS pathogenesis [140, 141] and Human Cytomegalovirus (HCMV) infection can suppress HIV infection by limiting availability of the coreceptor CCR5 on macrophages [142] . Infection with Hepatitis A Virus (HAV) can suppress infection with HCV and may actually promote clearance [143] . Evidence from mice supports the assertion that viruses can confer resistance to non-viral disease as well, as infection with murine gammaherpesvirus results in protection from challenge with Listeria [144] and Type 1 Diabetes can be prevented in mice infected with lymphotropic viruses [145] . Oncolytic viruses, which specifically target, infect, and kill tumor cells are also notable in both their novelty and their clinical utility (reviewed in [146] [147] [148] ). Viruses may even be able to provide developmental and immunological benefits not unlike that of the bacterial microbiota, as evidenced by the establishment of gut homeostasis in mice colonized with norovirus [149] . Endogenous retroelements could also presumably be included here in the case of their population of a nongermline subset of cells within an individual and conferral of benefit to the host.