Chapter 20 Microbial Diseases of the Nervous System and Eyes 2012 Pearson Education Inc Lecture prepared by Mindy Miller Kittrell North Carolina State University Structure of the Nervous System Divided into two parts Central nervous system CNS Peripheral nervous system PNS 2012 Pearson Education Inc Figure 20 1 The nervous system overview Structure of the 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 region 2012 Pearson Education Inc Structure of the Nervous System Structures of the Peripheral Nervous System Nerves transfer commands from CNS to muscles and glands Cranial nerves extend from brain through holes in the cranial bones Spinal nerves extend from spinal cord through vertebral gaps 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 CNS 2012 Pearson Education Inc Structure of the Nervous System Cells of the Nervous System Two basic cell types Neuroglia Provide support insulation nutrients phagocytize microbes Neurons Carry nerve impulses Nucleus lies in a region called the cell body Ganglion is collection of many neurons cell bodies Dendrites and axons extend from the cell body 2012 Pearson Education Inc Structure of the Nervous System Portals 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 Travel in peripheral neurons to the CNS Infect and kill cells of the meninges causing meningitis 2012 Pearson Education Inc Bacterial Diseases of the Nervous System Bacteria cause disease in two ways Infect cells of the nervous system Meningitis Leprosy Bacteria growing elsewhere release toxins that affect neurons Botulism Tetanus 2012 Pearson Education Inc Bacterial Diseases of the Nervous System Bacterial Meningitis Signs and symptoms Sudden high fever and severe meningeal inflammation Encephalitis can result in behavioral changes coma and death Can develop rapidly 2012 Pearson Education Inc Bacterial Diseases of the Nervous System Bacterial Meningitis Pathogens and virulence factors Five species cause 90 of bacterial meningitis cases Neisseria meningitidis Streptococcus pneumoniae Haemophilus influenzae Listeria monocytogenes Streptococcus agalactiae 2012 Pearson Education Inc Figure 20 2 Diplococci of Neisseria meningitidis Figure 20 3 Cells of Streptococcus pneumoniae Figure 20 4 The pleomorphic bacili of Haemophilus influenzae Pleomorphisms Figure 20 5 Listeria overview Bacterial Diseases of the Nervous System Bacterial Meningitis Pathogenesis S agalactiae acquired during birth Listeria transmitted via contaminated food Other species transmitted via respiratory droplets Epidemiology S pneumoniae present in throat of 75 of humans Not spread by casual contact Meningococcal meningitis can become epidemic 2012 Pearson Education Inc Bacterial Diseases of the Nervous System Bacterial Meningitis Diagnosis treatment and prevention Diagnosis based on symptoms and culturing of bacteria from CSF Treated with intravenous antimicrobial drugs Vaccines available for S pneumoniae H influenzae type b and N meningitidis Individuals at risk for listeriosis should avoid highrisk foods 2012 Pearson Education Inc Bacterial Diseases of the Nervous System Hansen s Disease Leprosy Signs and symptoms Tuberculoid leprosy nonprogressive Lepromatous leprosy progressive tissue destruction Pathogen and virulence factors Mycobacterium leprae is the causative agent Gram positive bacillus with mycolic acid in cell wall Pathogenesis M leprae grows best in cooler regions of the body M leprae can live inside infected cells for years 2012 Pearson Education Inc Figure 20 6 Lepromatous leprosy Bacterial Diseases of the Nervous System Hansen s Disease Leprosy Epidemiology Transmitted by person to person contact or breaks in the skin Diagnosis treatment and prevention Diagnosis based on the signs and symptoms Confirmed by presence of acid fast bacilli in samples Treated with multiple antimicrobials BCG vaccine provides some protection 2012 Pearson Education Inc Bacterial Diseases of the Nervous System Botulism Signs and symptoms Caused by intoxication from ingested toxin Three forms Foodborne botulism Infant botulism Wound botulism Pathogen and virulence factors Clostridium botulinum is the causative agent Different strains produce one of seven neurotoxins 2012 Pearson Education Inc Figure 20 7 Botulism toxin overview Bacterial Diseases of the Nervous System Botulism Epidemiology 50 cases of foodborne and wound botulism per year in U S Infant botulism most common form in U S Diagnosis treatment and prevention Three approaches to treatment Washing of intestinal tract to remove Clostridium Administration of botulism immune globulin Treatment with antimicrobial drugs Prevented by destroying endospores in contaminated food 2012 Pearson Education Inc Bacterial Diseases of the Nervous System Tetanus Signs and symptoms Lockjaw Spasms and contractions may spread to other muscles Pathogen and virulence factors Clostridium tetani is causative agent Produce neurotoxin called tetanospasmin 2012 Pearson Education Inc Figure 20 8 A patient with tetanus Figure 20 9 Tetanus toxin overview Bacterial Diseases of the Nervous System Tetanus Pathogenesis Can acquire through break in skin or mucous membrane Distance of infection from CNS determines incubation period Epidemiology Mortality rate is 50 if left untreated Diagnosis treatment and prevention Diagnosis based on characteristic muscle contraction Treated with passive immunotherapy antimicrobials active immunization Vaccine available against tetanus 2012 Pearson Education Inc Viral Diseases of the Nervous System Viruses more readily cross the bloodbrain barrier Occur more frequently than bacterial and fungal infections Include meningitis polio rabies and encephalitis 2012 Pearson Education Inc Viral Diseases of the Nervous System Viral Meningitis Signs and symptoms Similar to those of bacterial meningitis Usually milder than those of bacterial or fungal meningitis Pathogens and virulence factors 90 of cases caused by viruses in the genus Enterovirus Pathogenesis Damage to cells