Nervous System Infections Chapter 20

Nervous system Central nervous system (CNS) – Brain Encephalitis – Spinal cord Peripheral nervous system (PNS) – Bundles of thin extensions from nerve cells called axons

Two basic cell types Neuroglia – Provide support Neurons – Carry nerve impulses – Nucleus in the cell body – ganglion

Defenses Meninges – Meningitis Cerebrospinal fluid (CSF) Bone casing Blood-brain barrier

Structures of brain and spinal cord

Normal flora None Viruses can exist in a dormant state in the nervous system – penetrate CNS by traveling up nerve bundles – Herpes simplex and rabies viruses

Pathogens and virulence factors – Streptococcus pneumoniae – leading cause in adults – Neisseria meningitidis – epidemic, fimbriae, capsule, and endotoxin – Haemophilus influenzae – leading cause prior to vaccine – Listeria monocytogenes – listeriosis in fetuses, pregnant women, and immunocompromised individuals – Streptococcus agalactiae – causes most cases of newborn meningitis Bacterial Meningitis

Streptococcus Neisseria

Haemophilus Listeria

Signs and symptoms – Acute high fever and severe meningeal inflammation Inflamed cranial meninges – severe headache, vomiting, pain Inflamed spinal meninges – stiff neck, altered muscle control Encephalitis may cause behavioral changes, coma, and death Petechiae may appear on skin

Epidemiology S. agalactiae acquired during birth Listeria transmitted via contaminated food S. pneumoniae, Neisseria & Haemophilus all transmitted via respiratory droplets S. pneumoniae present in throat of 75% of humans without causing harm Meningococcal meningitis is the only form that becomes epidemic

Diagnosis – Based on symptoms and culturing of bacteria in CSF from spinal tap

Prevention Vaccines available for S. pneumoniae, H. influenzae, and N. meningitidis Individuals at risk for listeriosis should avoid high-risk foods (milk, cheeses, undercooked meat) Mass prophylaxis with ceftriaxone or rifampin helps control epidemics of meningococcal form Treatment ceftriaxone or penicillin

Tetanus “Lockjaw” Causative agent – Clostridium tetani Anaerobic Gram positive Bacillus Spore former

Signs & Symptoms – Tightening of jaw and neck muscles difficulty swallowing – Restlessness and irritability – Increased contractions spreading to other muscles Back spasms Difficulty breathing and death – Prolonged contraction of diaphragm

Bacteria contained to anaerobic tissue around wound Tetanospasmin toxin moves to CNS and blocks inhibition of motor neurons causing paralysis 50-90% mortality rate in untreated cases

Epidemiology – C. tetani found in dirt and dust and GI tract of humans and other animals – Nearly half of infections result from puncture wounds including Body piercing, tattooing, animal bites, IV drugs Frequently fatal but rare in the developed world – 30 to 60 cases reported in US annually

Prevention – Immunization with toxiod vaccine DTaP Treatment – Thoroughly clean wound Remove all dead tissue and foreign material – Penicillin to kill multiplying bacteria Will not destroy endospores – Antitoxin Neutralizes only circulating toxin