Presence of human herpesviruses 6, 7, and 8 DNA sequences in normal brain tissue

The three novel human herpesviruses (HHV) 6, 7, and 8 are predominantly, bu t not exclusively, lymphotropic. In an attempt to elucidate their neurotrop ism in vivo, viral DNA sequences present in fresh autopsy cortical brain ti ssues obtained from 84 consecutive Chinese subjects (mean age, 66.9 years; range, 21-98 years) were detected by a nested polymerase chain reaction. Th ese patients were apparently immunocompetent and free of clinical signs of viral diseases. HHV-6 DNA was detected in 36 of 84 (42.9%) patients, and th e DNA-positive and -negative groups did not show a significant difference i n age or sex distribution. Of the 36 HHV-6 DNA-positive cases, 9 (25%) were variant A and 27 (75%) were variant B. In view of the lower prevalence of variant A than variant B in the adult population, the two variants may shar e a comparable neuroinvasive potential. HHV-7 and HHV-8 DNA were detected r espectively in three and two patients. The low positive rates of HHV-7 and HHV-8 may represent a relatively lower neuroinvasive potential of: the viru ses. Alternatively, the localization of HHV-7 and HHV-8 may be more restric ted and the sampled cortical tissues may not represent the most abundant si te of persistence in the nervous system. The results provide molecular evid ence of the presence of the three newly identified herpesviruses in brain t issue. The pathogenic role for HHV-7 and HHV-8, as with HHV-6, in neurologi cal diseases should not be overlooked. (C) 1999 Wiley-Liss, Inc.