ACE and viral encephalitis: Although, there are no data on the assessment of serum ACE level in ON, systemic or local ACE levels have been investigated in various inflammatory conditions such as MS, sarcoidosis, rheumatoid arthritis, diabetes mellitus, and viral encephalitis [6–8] There is increasing evidence supporting a potential role for the renin-angiotensin system (RAS) in inflammatory diseases, and it has considerable physiological significance in CNS.