Autopsy brain samples from 51 controls and 57 patients who died with encephalopathy of unknown origin were tested for HHV-6 & HHV-7 using immunohistochemistry, nested and real time PCR. Patients with encephalopathy had a greater frequency of HHV-6 & 7 (89.4%) compared to controls (68.6%).
Also, HHV-6 DNA was found at high levels in both the temporal and frontal lobes, and it was found significantly more frequently in the frontal lobe in these patients than in the temporal lobe.
Patients with encephalopathy also had a significantly higher viral load in the olfactory tract as well as the pia mater, the loose vascular coat that encloses the surface of the cerebral cortex. The authors suggest that the viral load may be high in these locations because these tissues may be used as a pathway to enter the CNS.
There was no difference in HHV-6B viral load in the hippocampus between the patients and controls. Only HHV-6B DNA was found; no HHV-6A DNA could be detected.
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