nervous system infections chapter 20. nervous system central nervous system (cns) – brain...

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