Microbial Diseases of the Nervous System - In-depth Notes

Microbial Diseases of the Nervous System

Overview

  • Nervous System Components:

    • Central Nervous System (CNS): Brain and spinal cord.

    • Peripheral Nervous System (PNS): Nerves branching from CNS.

  • Meninges: Protective coverings of CNS.

    • Layers: Dura mater (outer), Arachnoid mater (middle), Pia mater (innermost).

    • Cerebrospinal Fluid (CSF): Found in the subarachnoid space, acts as a cushion.

  • Blood-Brain Barrier: Prevents harmful substances in blood from entering CNS.

Meningitis

  • Definition: Inflammation of the meninges.

  • Types: Bacterial and viral.

  • Common Symptoms: Fever, headache, stiff neck, nausea, vomiting, convulsions, and possibly coma.

  • Bacterial Meningitis: More severe than viral, can lead to serious complications.

Meningococcal Meningitis

  • Causative Agent: Neisseria meningitidis.

  • Characteristics:

    • Aerobic, gram-negative diplococcus.

    • Six serotypes, with capsular virulence factors and exotoxin.

  • Transmission: Begins as a throat infection, progresses to meningitis.

  • Symptoms: Characterized by a rash (ecchymosis) and bacteremia.

  • Mortality Rate: 9-12% with antibiotic treatment, up to 80% without.

  • Prevention: Vaccination against serogroups A, C, Y, W, and B.

Other Bacterial Meningitis Forms

  • Haemophilus influenzae type B (Hib):

    • Gram-negative; common in children.

    • Prevented with Hib vaccine.

  • Streptococcus pneumoniae:

    • Capsule protects against immune response; vaccinated to prevent.

Botulism

  • Causative Agent: Clostridium botulinum.

    • Produces a neurotoxin leading to flaccid paralysis.

    • Associated with improperly canned foods.

  • Types:

    • Food-borne: Ingestion of toxin.

    • Wound botulism: Infection of wounded tissue.

    • Infant botulism: Common in infants, related to honey ingestion.

  • Symptoms: Weakness, blurred vision, respiratory failure can lead to death.

  • Prevention: Proper food canning practices.

Tetanus

  • Causative Agent: Clostridium tetani (obligate anaerobe).

  • Mechanism: Tetanospasmin neurotoxin causes muscle spasms by blocking relaxation pathways.

  • Symptoms: Muscle rigidity and spasms, death can occur from respiratory muscles' spasms.

  • Prevention: Vaccination (DTaP), booster every 10 years.

Leprosy

  • Causative Agent: Mycobacterium leprae.

  • Forms:

    • Tuberculoid: Loss of sensation in skin patches.

    • Lepromatous: Disfiguring nodules form.

  • Treatment: Long-term antibiotics (Dapsone, Rifampin).

Viral Diseases

Poliomyelitis

  • Causative Agent: Poliovirus, transmitted via oral-fecal route.

  • Symptoms: Sore throat, nausea, paralysis in 1% of cases, results from nerve cell destruction.

  • Vaccines:

    • Salk (inactivated).

    • Sabin (oral, attenuated).

Rabies

  • Causative Agent: Rabies virus (Lyssavirus family).

  • Transmission: Animal bites.

  • Symptoms: Muscle spasms, hydrophobia, encephalitis; progresses towards coma.

  • Treatment: Postexposure prophylaxis (PEP) with vaccine and immune globulin.

Arboviral Encephalitis

  • Pathogens: Mosquito-borne viruses.

  • Examples: Eastern/western equine encephalitis, West Nile, St. Louis encephalitis.

  • Symptoms: Ranges from mild to severe neurological damage and higher mortality rates in older individuals.

Fungal Diseases

Cryptococcosis

  • Causative Agent: Cryptococcus neoformans.

  • Symptoms: Typically affects immunocompromised individuals; may cause CNS infections.

  • Transmission: Inhalation of spores from contaminated soil.

  • Treatment: Amphotericin B, flucytosine.

Protozoan Diseases

African Trypanosomiasis

  • Causative Agents: Trypanosoma brucei gambiense and rhodesiense.

  • Vector: Tsetse fly.

  • Symptoms: Fever, headache, progression to CNS impairment.

  • Treatment: Eflornithine crosses blood-brain barrier.

Amoebic Meningoencephalitis

  • Causative Agent: Naegleria fowleri; fatal infection through nasal mucosa from contaminated water.

  • Symptoms: Rapidly progressive neurological impairment.

Prion Diseases

  • Mechanism: Abnormal proteins (prions) cause normal proteins in brain to misfold, leading to spongiform degeneration.

  • Examples: Creutzfeldt-Jakob disease (CJD), bovine spongiform encephalopathy (BSE).