Central Nervous System Infections

Posted by e-Medical PPT Monday, April 4, 2011
Central nervous system infections are usually:
Blood-borne invasion; most common
         (e.g. polioviruses or Neisseria meningitidis)
Invasion via peripheral nerves; less common     
      (e.g. herpes simplex, varicella-zoster, rabies)
Blood-borne invasion takes place across:
     - blood-brain barrier (encephalitis)
     - blood-cerebrospinal fluid (CSF) barrier (meningitis)

Invasion via peripheral nerves:
* Herpes simplex virus (HSV) and varicella-zoster virus (VZV) present in skin or mucosal lesions travel up axons to reach the dorsal root ganglia.
* Rabies virus, introduced into muscle tissues by:  
     - bite of a rabid animal
     - It enters peripheral nerves and travels to CNS,     
         to reach the neurons

Pathologic consequences of CNS infection
In CNS; viruses infect neural cells, sometimes showing a marked preference
Polio and rabies viruses invade neurons. CJD virus invades oligodendrocytes
Spread of infection is direct from cell to cell along established nervous pathways
Bacteria and protozoa induce brain abscesses

* Meningitis is one of the most terrifying disease
* It can be fatal in hours
* Early symptoms resemble
    self-limiting conditions
    (flu and colds)
Most common causes of meningitis are:
  a) Bacterial infections (Septic meningitis)
       may result in death or brain damage.
  b) Viral infections (Aseptic meningitis)
       usually resolve without treatment.

Bacterial Meningitis (Septic Meningitis)
Pneumococcal, Streptococcus pneumoniae (38%)
Meningococcal, Neisseria meningitidis (14%)
Haemophilus influenzae (4%)
Staphylococcal, Staphylococcus aureus (5%)
Tuberculous, Mycobacterium tuberculosis

Viral Meningitis (Aseptic meningitis)
Etiological Agents:
Enteroviruses, most common (Coxsackie and Echovirus)
Measles virus
Herpes Simplex virus
Varicella Zoster virus

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