Detection of human herpesviruses 6 and 7 genomic sequences in brain tumours

Background - Human herpesviruses 6 and 7 (HHV-6, HHV-7) are ubiquitous, with primary infection occurring early in life followed by persistence, which may involve neural tissue. While HHV-6 and HHV-7 are predominantly T lymphotropic, the extent of tissue tropism in persistent infection is not known. Aim - To investigate neuropersistence and the role of HHV-6 and HHV-7 in brain tumorigenesis. Methods - Nested polymerase chain reaction was used to detect HHV-6 and HHV-7 genomic sequences in preparations of total DNA extracted from 98 formalin fixed, praffin embedded primary brain tumours. HHV-6 detected was further characterised into variants A and B by restriction fragment length analysis. Results - HHV-6 was detected in 8.2% of cases and HHV-7 in 14.3% (14/98). None of the positive samples contained both viruses. Among the eight HHV-6 positive tumours, three harboured variant A and five variant B. Four of the five ependymomas studied contained viral DNA. Otherwise, both HHV-6 and HHV-7 were present at similar low frequencies in most of the tumour types investigated. Conclusions - The findings do not support an aetiological role of HHV-6 and HHV-7 in primary brain tumour, but they suggest that HHV-6 and HHV-7 are neurotropic in vivo and that the central nervous system seems to be one of the reservoirs for persistent infection.