HHV-7 in adults with drug-resistant epilepsy: a pathological role in hippocampal sclerosis?

Human herpesvirus-7 (HHV-7) is a β-herpesvirus associated with febrile seizures. No association between HHV-7 and epilepsy has been confirmed.

The aim of this study was to investigate the presence of HHV-7 protein (KR4) in brain tissue from patients with drug-resistant epilepsy and to determine whether inflammatory molecules are activated in the presence of HHV-7 infection.

We used immunohistochemistry (IHC) to detect HHV-7 protein KR4 in samples from 305 patients with drug-resistant epilepsy. Liquid nitrogen-preserved hippocampal sclerosis (HS) samples from 63 of these patients were available, and we used nested polymerase chain reaction (PCR) to detect HHV-7 DNA. Inflammatory molecules including tumor necrosis factor-alpha (TNF-α), transforming growth factor-beta (TGF-β), interleukin-1 (IL-1) and interleukin-6 (IL-6) were identified by real-time PCR (rt-PCR) and IHC.

The study sample included 201 male subjects. The mean age was 23.9, SD 6.2 years (range 15-45). HS was the pathology in 69 samples (23%). The HHV-7 protein was detected in 27 (9%) of the 305 samples and in none of the 42 controls. The factors associated with HHV-7 infection were HS (11/69), glial scar (8/58), arachnoid cyst (2/21), focal cortical dysplasia (2/31) and vascular malformation (4/52). HHV-7 antigen was distributed mainly in the cytoplasm of astrocyte and oligodendrocyte in HS samples. HHV-7 DNA was detected in 20 of the 63 nitrogen preserved HS samples. The expression of TGF-β was up-regulated in samples that were positive for the HHV-7 protein and was mainly detected in neurons. This finding suggests a possible association between HHV-7 positivity, activation of TGF-β and drug-resistant epilepsy, especially HS, but these data need to be replicated.