Prevalence and distribution of human herpesvirus 6 variants A and B in adult human brain

The presence of human herpesvirus 6 (HHV-6) in brain tissues of 40 consecut ive post-mortem cases was examined. For each case, autopsy samples were col lected from the cerebellum, frontal, temporal, parietal and occipital lobes of both sides of the brain. HHV-6 DNA was detected by nested polymerase ch ain reaction and characterised into variants A and B. Overall, 97/400 (24.3 %) samples were positive for HHV-6 DNA with 16 being variant A and 81 being variant B, but none of the samples harboured both variants. When analysed by patient, 34/40 (85%) had HHV-6 DNA detected in the brain. The viral DNA positivity did not show significant variation with gender and age. Four pat ients harboured variant A, 23 harboured variant B, and seven had both varia nts at different positions. The results indicate that both HHV-6A and HHV-6 B are neurotropic and human brain may be another site for latency. HHV-6B w as detected in brain tissues of a majority (75%) of the studied population and with a widespread distribution within the brain. Although the observed prevalence of HHV-6A in brain is lower (27.5%), in view of its lower seropr evalence, the neuroinvasive potential of variant A may be comparable to tha t of variant B. Although both variants are potential pathogens for the nerv ous system, the fact that they can exist, probably for most of the time, as commensals in human brain needs to be considered when interpreting their r oles in neuropathology. J. Med. Virol. 64:42-46, 2001. (C) 2001 Wiley-Liss.