Slide 1Structure of the Nervous SystemStructures of the Central Nervous SystemStructures of the Peripheral Nervous SystemDefenses that Protect the Nervous SystemPortals of Infection of the Central Nervous SystemBacterial Meningitis – Pathogens and Virulence FactorsStreptococcus pneumoniae – Pathogen and Virulence FactorsStreptococcus pneumoniae – Pathogen and Virulence FactorsNeisseria meningitidis – Pathogen and Virulence FactorsNeisseria meningitidis – Pathogen and Virulence FactorsBacterial Meningitis – PathogenesisBacterial Meningitis – Signs and SymptomsBacterial Meningitis – Signs and SymptomsStreptococcus pneumoniae – EpidemiologyNeisseria meningitidis - EpidemiologyBacterial Meningitis - DiagnosisBacterial Meningitis - TreatmentStreptococcus pneumoniae - PreventionNeisseria meningitidis - PreventionViral Diseases of the Nervous SystemViral Meningitis – Pathogens and Virulence FactorsViral Meningitis - PathogenesisViral Meningitis – Signs and SymptomsViral Meningitis – EpidemiologyViral Meningitis – DiagnosisViral Meningitis – TreatmentViral Meningitis – PreventionM I C R O B I O L O G YWITH DISEASES BY BODY SYSTEM SECOND EDITIONChapter 20Microbial Diseases of the Nervous System and EyesTHIRDStructure of the Nervous System•Divided into two parts–Central nervous system (CNS)–Peripheral nervous system (PNS)Structures of the Central Nervous System•Composed of the brain and spinal cord•Brain has several main parts–Cerebrum controls voluntary muscles, perception, and “thinking”–Cerebellum controls many involuntary body movements–Brain stem controls breathing, heart rate, blood pressure•Spinal cord–Extends from the brain stem to the lumbar regionStructures of the Peripheral Nervous System•Composed of nerves that transfer commands from CNS to muscles and glands and provide information to the CNS concerning events in the body•Cranial nerves extend from the brain through holes in the cranial bones•Spinal nerves extend from the spinal cord through gaps between the vertebrae•Three types of nerves–Sensory nerves – carry signals toward the CNS–Motor nerves – carry signals away from the CNS–Mixed nerves – carry signals toward and away from the CNSDefenses that Protect the Nervous System•Brain encased within the bony skull•Spinal cord is protected by vertebrae•Brain and the spinal cord are further protected by the meninges•CSF circulates around the brain and spinal cord between the layers of the meninges–CSF adds to the protection because it absorbs some of the shock of an injury•CNS is protected against chemical injury by the blood-brain barrierPortals of Infection of the Central Nervous System•CNS is an axenic environment–It has no normal microbiota•Pathogens may access the CNS several ways–Breaks in the bones and meninges–Medical procedures –Traveling in peripheral neurons to the CNS–Carried by blood or lymph and breach blood-brain barrier–Circulation of cerebrospinal fluidBacterial Meningitis – Pathogens and Virulence Factors•Over 50 species of bacteria can cause meningitis–Some are opportunists•Five species cause 90% of bacterial meningitis cases–Streptococcus pneumoniae–Neisseria meningitidis –Haemophilus influenzae –Listeria monocytogenes–Streptococcus agalactiaeStreptococcus pneumoniae – Pathogen and Virulence Factors•Gram-positive coccus; usually in pairs (pneumococcus)•92 different strains known to infect humans•Normal flora of throat that opportunistically colonize lungs, sinuses, and middle ear•Move into the meninges via the bloodStreptococcus pneumoniae – Pathogen and Virulence Factors•During invasion, capsule is essential determinant of virulence – protects from digestion following phagocytosis•Secretory IgA protease – destroys IgA•Pneumolysin – interferes with the action of lysosomes•Phosphorylcholine in cell wall binds to receptors on cells in lungs, meninges, and blood vessel walls–Stimulates target cells to endocytose them–Hidden inside body cells–Organisms can then cross from these cells into the blood and brainNeisseria meningitidis – Pathogen and Virulence Factors•Gram-negative diplococcus•13 antigenic strains; A, B, C, and W135 cause most cases of disease in humans•Known as meningococcus•NonmotileNeisseria meningitidis – Pathogen and Virulence Factors•Fimbriae•Polysaccharide capsule that resists lytic enzymes of the body’s phagocytes–Organisms survive, reproduce, and are carried throughout the body within neutrophils and macrophages•Lipooligosaccharide (LOS; cell wall antigen) composed of lipid A and sugars – released from outer membrane into extracellular spaces and triggers fever, vasodilation, inflammation, shock, and disseminated intravascular coagulation (DIC)–Bacterium sheds extrusions of its outer membrane•Avirulent strains lack fimbriae, capsule, and lipooligosaccharideBacterial Meningitis – Pathogenesis•Humans inhale organisms in respiratory droplets from infected individuals (droplet transmission) who may be asymptomatic (carriers)–N. meningitidis is a common member of the normal flora in the upper respiratory tracts of up to 40% of healthy people–Chronic irritation or damage to pharyngeal and respiratory mucosa may be predisposing factor for invasive disease•Bacteria spread to meninges from infections of the lungs, sinuses, or inner ear or via the blood•Bacteria are somewhat protected by their capsules from phagocytosis•Metabolize glucose in the CSFBacterial Meningitis – Signs and Symptoms•Cases characterized by increased number of WBC in CSF, sudden high fever, and intense meningeal inflammation–Swelling retards normal flow of CSF and causes pressure to build up •Inflamed cranial meninges – severe headache, nausea, vomiting, pain, loss of brain functions leading to drowsiness, confusion, fretfulness, or irritability•Inflamed spinal meninges puts pressure on surrounding nerves and muscles–Stiffness in neck–Affects sensory input and motor controlBacterial Meningitis – Signs and Symptoms•Infection of the brain (encephalitis) can result in deafness, blindness, behavioral changes, coma, and death•Signs and symptoms develop swiftly–Meningococcal meningitis can kill within 6 h•Dramatic increase in WBC in CSF (milky white in color)•Petechiae present in 30-60% of cases of meningococcal meningitisStreptococcus pneumoniae –