Post on 30-Dec-2015
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