Comprehensive Study Notes: Microbial Diseases of the Nervous System
Nervous System: Basics
The nervous system includes the brain, spinal cord, and all nerves.
It has two main parts:
Central Nervous System (CNS): Brain and spinal cord.
Peripheral Nervous System (PNS): Nerves outside CNS.
CNS Protection (Meninges)
CNS has the BRAIN and SPINAL CORD.
They are protected by three layers called meninges:
Dura mater: Outer layer.
Arachnoid membrane: Middle layer.
Pia mater: Inner layer.
Subarachnoid space: Between arachnoid and pia mater, filled with CSF.
Cerebrospinal Fluid (CSF)
CSF is a fluid in the subarachnoid space.
Made of: Water, proteins, glucose, sodium, chloride.
Functions:
Protects brain and spinal cord.
Provides nutrients.
Removes waste.
How to get it: Lumbar puncture (LP).
Lumbar Puncture (LP)
LP: Procedure to collect CSF from the lower spine.
Done by inserting a needle into the lower back.
Precautions: Do only when necessary, check for bleeding issues, avoid infected sites.
CSF Analysis: Normal vs. Infections
CSF is analyzed to find CNS infections. Tests include appearance, microscopy, culture, biochemical tests, and antigen/antibody tests.
Samples are collected in 3 bottles; bottle 3 is best for bacteria to avoid skin contamination.
Normal CSF:
Appearance: Clear
WBC/μL:
Protein:
Glucose:
Chloride:
Pressure: Normal
Acute Bacterial Meningitis:
Appearance: Turbid (cloudy)
WBC/μL: High (thousands; mainly neutrophils)
Protein: High
Glucose: Low
Chloride: Low
Pressure: High
Viral Meningitis:
Appearance: Clear
WBC/μL: Increased (mainly lymphocytes)
Protein: Slightly increased
Glucose: Normal
Chloride: Normal
Pressure: Normal to increased
Tubercular Meningitis (TBM):
Appearance: Slightly opaque; may have cobweb-like formations
WBC/μL: (mainly lymphocytes)
Protein: Increased
Glucose: Decreased
Chloride: Decreased
Pressure: Increased
Fungal Meningitis:
Appearance: Clear to slightly cloudy
WBC/μL: (mixed or lymphocytic)
Protein: Increased
Glucose: Decreased
Chloride: Decreased
Pressure: Increased
How Germs Enter the Nervous System
Routes: Skull/backbone fractures, medical procedures, peripheral nerves, blood/lymph.
Common causes: Bacteria, viruses, fungi.
Meningitis: Inflammation of meninges (protective brain/spinal cord layers).
Encephalitis: Brain inflammation (usually viral).
Lab Diagnosis of CNS Infections
CSF is the main sample.
Procedures:
Visual appearance
Microscopy (cell counts, stains like Gram, Ziehl-Neelsen, negative stain for fungi; wet prep for live organisms)
Culture (different media for normal vs. raised WBC, specific media for TB/fungi)
Biochemical analysis
Antigen/antibody detection tests (ELISA, PCR)
Specific Nervous System Infections
Haemophilus influenzae Meningitis:
Cause: Gram-negative bacterium.
Affects: Children 6 months to 4 years.
Prevention: Hib vaccine.
Neisseria meningitidis Meningitis (Meningococcal Meningitis):
Cause: Gram-negative bacterium with capsule.
Carriers: ~10% are healthy carriers.
At risk: Children <1 year, adults ≥65.
Spread: Respiratory secretions.
Prevention: Vaccines.
Streptococcus pneumoniae Meningitis (Pneumococcal Meningitis):
Cause: Gram-positive bacterium.
Carriers: ~70% carry it in nose/throat.
Common: Children 1 month to 4 years.
Prevention: PCV13 and PPSV23 Vaccines.
Listeriosis (Listeria monocytogenes):
Cause: Gram-positive rod.
At risk: Pregnant/newborns, ≥65, immunocompromised.
Spread: Food (dairy, meat, produce).
Tetanus:
Cause: Clostridium tetani (Gram-positive, spore-forming, anaerobe).
Disease: Muscle spasms, especially jaw/neck.
Toxin: Tetanospasmin (blocks muscle relaxation).
Prevention: Tetanus toxoid vaccine.
Treatment: Tetanus immune globulin.
Botulism:
Cause: Clostridium botulinum (Gram-positive, spore-forming, anaerobe).
Toxin effect: Blocks nerve signals to muscles, causing floppy paralysis.
Types: Foodborne, infant, wound.
Symptoms: Difficulty swallowing, double vision, muscle weakness, breathing issues.
Treatment: Botulinum antitoxin.
Prevention: Safe canning, nitrites in meats.
Leprosy:
Cause: Mycobacterium leprae (acid-fast rod).
Targets: Peripheral nerves, skin.
Spread: Prolonged close contact.
Forms: Tuberculoid (loss of sensation), Lepromatous (disfiguring nodules).
Poliomyelitis (Polio):
Cause: Poliovirus.
Spread: Contaminated food/water.
Effect: Can destroy motor cells, causing paralysis (rare).
Prevention: Inactivated polio vaccine (eIPV).
Rabies:
Cause: Rabies virus (Rhabdovirus).
Spread: Bites of infected animals.
Effect: Multiplies in muscle, spreads to CNS causing brain inflammation.
Symptoms: Fever, headache, then agitation, hydrophobia.
Prevention: Pre-exposure vaccine; post-exposure vaccine + immune globulin.
Arboviral Encephalitis:
Cause: Viruses (many types).
Spread: Arthropods (mosquitoes, ticks).
Prevention: Vector control, some vaccines exist.
Cryptococcus neoformans:
Cause: Fungus.
Found: Soil, bird droppings.
Spread: Inhalation of spores.
Leads to: Cryptococcal meningitis.
Treatment: Antifungals.
African Trypanosomiasis (Sleeping Sickness):
Cause: Protozoan parasites (Trypanosoma brucei).
Spread: Tsetse fly bite.
Effect: Chronic (gambiense) or acute (rhodesiense) disease.
Naegleria fowleri:
Cause: Free-living amoeba.
Found: Freshwater.
Infection: Contaminated water enters nose (e.g., swimming).
Effect: Travels to brain, causes severe brain destruction.
Transmissible Spongiform Encephalopathies (TSEs):
Cause: Abnormal prion proteins.
Effect: Misfolded proteins damage brain, causing 'spongy' changes and fatal neurodegeneration.
Spread: Contaminated meat, infected tissues, inheritance.
Types: Sheep scrapie, Creutzfeldt-Jakob disease (CJD), Kuru, Bovine spongiform encephalopathy (BSE).
Key Takeaways
CSF analysis helps diagnose CNS infections and guides treatment.
Understanding infection entry helps prevent them.
Vaccination is key for prevention (Hib, N. meningitidis, PCV, polio, tetanus).
Wide range of agents (bacteria, viruses, fungi, parasites, prions) infect CNS, requiring diverse diagnostic methods.
Public health actions: vaccine access, vector control, food safety, smart antibiotic use.