Abstract
DNA was extracted from the brains of patients with Alzheimer-type dementia, schizophrenia, Huntington's chorea and from patients without neurological disease, and examined for the presence of herpes simplex virus type 1 and human cytomegalovirus sequences. By selecting cloned virus DNA fragments which do not hybridize to normal human DNA we were able to achieve a detection level assessed on reconstruction experiments of 1 virus genome per 50 cells. Screening at such sensitivity did not detect virus sequences in the higher CNS, except in cases of encephalitis or immunosuppression. We conclude that, at this level of sensitivity, these viruses cannot be regarded as normal residents of the higher CNS, and at the time of death they do not appear to be associated with these neuropsychiatric conditions.