Download Nervous System Infections

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
Bacterial Meningitis
• 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
Neisseria
Streptococcus
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