Herpes virus particles, coloured transmission electron micrograph (TEM). Each particle (virion) of this virus, the HHV-6 (human herpes virus-6), consists of a double stranded deoxyribonucleic acid (DNA) genome surrounded by an icosahedral capsid (yellow), which is itself surrounded by an envelope covered in glycoprotein spikes (blue). HHV-6 infects white blood cells, specifically T lymphocytes, (one of which is partially seen at top right). It can cause encephalitis and seizures. After the primary infection the virus lays dormant in the body's cells and may be reactivated. Recent research suggests it may also play a role in some chronic neurological conditions such as MS, mesial temporal lobe epilepsy and chronic fatigue syndrome.