Leucocytes infected with herpes virus, light micrograph (LM). Inclusion bodies (dark purple) can be seen within the nucleus (purple) and cytoplasm (blue) of the leucocytes (white blood cells). These are viral capsid proteins that represent sites of viral multiplication. The virus responsible, HHV-6 (human herpes virus-6), is a double stranded DNA (deoxyribonucleic acid) virus that infects human leucocytes, specifically T lymphocytes. HHV-6 can cause encephalitis and seizures during a primary infection or when reactivated from latency in immunosuppressed patients. 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. Sample stained with haematoxylin and eosin.