Microbial Diseases of the Nervous System - Study Notes

Structure and Function of the Nervous System

  • Central Nervous System (CNS): Comprises the brain and spinal cord.
  • Peripheral Nervous System (PNS): Encompasses nerves branching from the CNS.
  • Meninges: Three protective layers surrounding the CNS:
    • Dura mater: Outermost layer.
    • Arachnoid mater: Middle layer.
    • Pia mater: Innermost layer.
  • Subarachnoid Space: Contains cerebrospinal fluid (CSF).
  • Blood-Brain Barrier: A filtering mechanism protecting the brain and spinal cord from harmful substances.

Meningitis and Encephalitis

  • Meningitis: Inflammation of the meninges.
  • Encephalitis: Inflammation of the brain.
  • Meningoencephalitis: Inflammation of both the meninges and the brain.

Bacterial Meningitis

  • Symptoms:
    • Initial: fever, headache, stiff neck.
    • Progression: nausea, vomiting, convulsions, coma.
  • Death can occur from shock/inflammation, often due to:
    • Endotoxins from gram-negative bacteria.
    • Cell wall fragments from gram-positive bacteria.
Haemophilus Influenzae
  • Type: Gram-negative aerobic bacteria.
  • Pathogenicity: Capsule antigen type b.
  • Affected Population: Mainly children (6 months to 4 years).
  • Preventive Measure: Hib vaccine.
Neisseria Meningitidis
  • Type: Aerobic, Gram-negative diplococcus with a capsule.
  • Transmission: Through aerosol droplets/contact with secretions.
  • Symptoms: Throat infection, bacteremia, meningitis; includes a characteristic rash.
  • Mortality Rate: 10-15% with antibiotic therapy, especially concerning for children (could cause deafness).
Streptococcus pneumoniae
  • Type: Gram-positive, encapsulated diplococcus.
  • Affected Demographic: Mainly children (1 month to 4 years), elderly at higher risk.
  • Mortality Rates: 8% in children, 22% in the elderly.
  • Preventive Strategy: Conjugate vaccine.

Diagnosis and Treatment

  • Diagnosis Methods:
    • Sample CSF via spinal tap; check for pathogens, Gram stain, culture, latex agglutination tests.
  • Treatment: Begin chemotherapy with broad-spectrum third-generation cephalosporins before final diagnosis.

Other Bacterial Diseases

Listeriosis
  • Causative Agent: Listeria monocytogenes, a foodborne illness linked to deli meats and unpasteurized dairy.
  • Risk Group: Infants, pregnant women (can lead to stillbirth).
  • Treatment: Penicillin.
Tetanus
  • Causative Agent: Clostridium tetani, found in contaminated soil.
  • Mechanism: Releases tetanospasmin neurotoxin, leading to muscle spasms.
  • Prevention: Vaccination with DTaP, requiring boosters every 10 years.
Botulism
  • Causative Agent: Clostridium botulinum, found in improperly preserved foods.
  • Symptoms: Flaccid paralysis due to toxin affecting nerves.
  • Treatment: Respiratory assistance and antitoxins.
Leprosy (Hansen’s Disease)
  • Causative Agent: Mycobacterium leprae.
  • Symptoms: Loss of sensation (tuberculoid form) or disfiguring nodules (lepromatous form).
  • Treatment: Antibiotics (Dapsone, Rifampin).

Viral Diseases

Poliomyelitis
  • Causative Agent: Poliovirus.
  • Transmission: Ingestion of contaminated water (fecal-oral route).
  • Symptoms: Mild throat infection, potential paralysis in <1% of cases.
  • Vaccination: Salk (inactivated) and Sabin (oral) vaccines.
Rabies
  • Causative Agent: Rabies virus (Lyssavirus).
  • Transmission: Animal bites, common in bats and other wildlife.
  • Symptoms: Encephalitis causes aggressive behavior or paralysis.
Arboviral Encephalitis
  • Causative Agents: Several mosquito-borne viruses (e.g., EEE, WEE, West Nile virus).
  • Symptoms: Can vary from mild to severe, with potential long-term neurological damage.

Fungal Diseases

Cryptococcal Meningitis
  • Causative Agent: Cryptococcus neoformans.
  • Transmission: Respiratory (from contaminated droppings).
  • Mortality: Up to 30% in immunocompromised individuals.

Protozoan Diseases

African Trypanosomiasis
  • Causative Agent: Trypanosoma brucei.
  • Symptoms: Neurological deterioration leading to coma and death.
  • Transmission: Tsetse fly bites.
Amoebic Meningoencephalitis
  • Causative Agent: Naegleria fowleri.
  • Transmission: Through nasal mucosa during swimming; lethal.

Diseases Caused by Prions

  • Characteristics: Self-replicating infectious proteins causing abnormal protein folding (TSEs).
  • Examples:
    • Scrapie (sheep)
    • Creutzfeldt-Jakob disease (humans)
    • Bovine spongiform encephalopathy (mad cow disease).

Vertical Transmission of Disease

  • Congenital Infections: Can significantly damage the fetus, affecting development (e.g. Zika virus, neonatal herpes).
  • Screening: TORCH screen tests for vertical transmission in pregnant women.