Multiple sclerosis and Kaposi's sarcoma - Chronic diseases associated withnew human herpesviruses?

Two diseases that for many years have been suspected to be of viral origin are multiple sclerosis (MS) and Kaposi's sarcoma (KS). With the use of a ne w technique called representational difference analysis both these diseases have recently been associated with new lymphotropic herpesviruses, i.e. hu man herpesviruses (HHV) 6 and 8. HHV-6 is a ubiquitous virus and the etiolo gical agent of exanthema subitum. Viral neuroinvasion occurs frequently in primary HHV-6 infection, and meningitis, encephalitis and demyelination hav e been described as rare complications. A relation with MS has been suggest ed for HHV-6, as the virus has been detected in MS plaques in the brain. Da ta from different studies are, however, conflicting and a definitive role f or HHV-6 in MS pathogenesis has not been established. HHV-8 is believed to be the causative agent of KS, and is also associated with some rare hematol ogical malignancies. The viral genome contains several potential oncogenes that are believed to have been picked up from the human genome during evolu tion. The role of HHV-8 in healthy, immunocompetent individuals is however uncertain. In conclusion, the full spectrum or human diseases associated wi th these new viruses is not yet understood, and rapid developments in molec ular biology will continue to shed new light on the interactions between he rpesviruses and their hosts.