Ch 22: Microbial Diseases of the Nervous System

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Central nervous system (CNS)

brain and spinal cord


Peripheral nervous system (PNS)

nerves that branch from the CNS


Blood–brain barrier

a filtering mechanism of the capillaries that carry blood to the brain and spinal cord tissue, blocking the passage of certain substances.



inflammation of the meninges



inflammation of the brain

Whole brain = Encephelon



inflammation of meninges and brain


Bacterial Meningitis

  • Initial symptoms of fever, headache, and a stiff neck. Followed by nausea and vomiting
  • May progress to convulsions and coma
  • Death from shock and inflammation
  • Due to endotoxin and cell wall release
  • Viral meningitis is more common and mild

Haemophilus influenza Meningitis

  • Gram-negative aerobic bacteria; normal throat microbiota
  • Prevented by the Hib vaccine
  • Accounts for 45% of bacterial meningitis cases; 6% mortality

Neisseria meningitidis Meningitis (Meningococcal Meningitis)

  • Gram-negative aerobic cocci with a capsule
  • Mortality of 9–12% with antibiotic therapy; 80% without
  • Outbreaks common in dorms and military barracks

Streptococcus pneumoniae Meningitis (Pneumococcal Meningitis)

  • Gram-positive encapsulated diplococcus
  • Also causes pneumonia and otitis media
  • Most common in children (1 month to 4 years)
  • Mortality: 30% in children, 80% in the elderly
  • Prevented by conjugated vaccine

Diagnosis and Treatment of the Most Common Types of Bacterial Meningitis

  • Sample CSF via a spinal tap or lumbar puncture
  • Latex agglutination tests
  • Chemotherapy initiated before diagnosis


  • Listeria monocytogenes. Gram-negative aerobic rod
  • Usually foodborne and asymptomatic
  • Can invade the bloodstream, causing sepsis
  • Reproduces in phagocytes. Spread phagocyte-to-phagocyte•Infects pregnant women, crossing the placenta and leading to stillbirth


  • Clostridium tetani•Gram-positive, endospore-forming, obligate anaerobe
  • Tetanospasmin (TeNT) – exotoxin released from vegetative cells. Enters CNS. Blocks the relaxation pathway in muscles, causing muscle spasms
  • Death occurs from spasms of respiratory muscles. Lockjaw
  • Prevented by vaccination with tetanus toxoid (DTaP). Stimulates antibodies that neutralize the toxin. Booster required every 10 years
  • Mortality of 25–50%
  • Treatment with tetanus immune globulin (TIG) and Infected tissue removed via debridement


  • clostridium botulinum: Gram-positive, endospore-forming, obligate anaerobe
  • Intoxication comes from ingesting the botulinal exotoxin (most potent toxin known)
  • Specific for the synaptic end of the nerve. Blocks release of the neurotransmitter acetylcholine, causing flaccid paralysis. Death usually comes from respiratory or cardiac failure
  • Treatment with respiratory assistance and antitoxins (BIG) and Prevented with proper canning and the use of nitrites in foods

Leprosy or Hensen's Disease

  • Mycobacterium leprae: Acid-fast rod
  • Grows in peripheral nerves and skin cells.
  • Survives macrophages and invades the myelin sheath
  • Transmission requires prolonged contact with an infected person or the inhalation of secretions
  • Diagnosed with a skin biopsy or skin smear
  • Treatment with antibiotics (Dapsone or Rifampin). Dapsone (inhibits folic acid synthesis similar to sulfonamides)•Rifampin (inhibits bacterial RNA-polymerase)


  • Tuberculoid (neural) form
  • Lepromatous (progressive) form
  • loss of sensation in skin areas
  • disfiguring nodules over the body; mucous membranes are affected

Poliomyelitis (caused by the poliovirus)

  • Transmitted by the ingestion of water containing feces containing the virus
  • Initial symptoms: sore throat and nausea.
  • Viremia may occur; enters the CNS, destruction of motor cells
  • Death from respiratory failure
  • Postpolio syndrome: muscle weakness occurring decades after infection
  • Salk vaccine (IPV): inactivated vaccine; injectable
  • Sabin vaccine (OVP): attenuated vaccine; oral; lifelong immunity


  • Enveloped, ssRNA virus. Genus Lyssavirus; bullet shape
  • Usually transmitted by the saliva of an animal bite
  • Can also cross mucous membranes
  • Initial symptoms: muscle spasms of the mouth and pharynx; hydrophobia
  • The virus multiplies in the skeletal muscles and travels through PNS to the brain cells, causing encephalitis
  • Average incubation of 30 to 50 days

Rabies Test and vaccines

  • Diagnosed from bodily fluids with the direct fluorescent-antibody (DFA) test
  • Pre-exposure schedule: 3 doses killed virus
  • Post-exposure prophylaxis (PEP): 4 doses of killed virus plus immune globulin
  • Human diploid cell vaccine (HDCV) & Human rabies immune globulin (RIG)

Cryptococcus neoformans Meningitis (Cryptococcosis)

  • Soil fungus associated with pigeon and chicken droppings
  • Transmitted by the respiratory route
  • In the immunocompromised, it spreads through blood to the CNS
  • Mortality of up to 30%
  • Treatment: amphotericin B and flucytosine

African Trypanosomiasis

  • Trypanosoma brucei gambiense
  • Transmitted from animals to humans by tsetse fly
  • Few early symptoms, followed by fever, headache, and deterioration of the CNS
  • Parasite evades antibodies through antigenic variation
  • Treated with eflornithine: crosses the blood-brain barrier; blocks an enzyme necessary for the parasite
  • Prevention: elimination of tsetse fly vectors

Amebic Meningoencephalitis

  • Naegleria fowleri: Causes primary amebic meningoencephalitis (PAM). Protozoan infects the nasal mucosa from swimming water, penetrates the brain, and feeds on brain tissues, “100% fatal”
  • Acanthamoeba: Causes granulomatous amebic encephalitis (GAE). Granulomas form around the site of infection, forming multiple lesions around the brain

Nervous System Diseases Caused by Prions

  • Chronic wasting disease
  • Creutzfeldt-Jakob disease (CJD)
  • Kuru
  • Bovine spongiform encephalopathy (BSE)
  • Sheep scrapie