Although the blood-brain barrier protects the nervous system from microorganisms, it may be damaged by bacteria, viruses, fungi, and other organisms. If damage occurs, resistance to infection of the nervous system is decreased. The major classes of inflammatory disease are meningitis and encephalitis (infections of the meninges, or covering membranes, of the brain and of the brain itself, respectively) and abscesses, which may be situated outside or just below the meninges or in the brain itself. Some viruses lie almost dormant within neural tissue for years before causing destruction. The measles virus may do this, causing a chronic progressive encephalitis ...(100 of 20416 words)