Microbial Diseases of the Nervous System: Study Guide

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Microbial Diseases of the Nervous System

Basic Anatomy of the Nervous System

The nervous system is responsible for coordinating and controlling bodily functions. It is divided into two main parts: the Central Nervous System (CNS) and the Peripheral Nervous System (PNS).

CNS: Consists of the brain and spinal cord. It processes information and directs responses.
PNS: Composed of nerves outside the CNS. It transmits signals between the CNS and the rest of the body.

Anatomy of the Meninges

The meninges are protective membranes surrounding the brain and spinal cord. They consist of three layers:

Dura mater: The tough, outermost layer.
Arachnoid mater: The middle, web-like layer.
Pia mater: The delicate, innermost layer that adheres to the CNS tissue.

Meningitis

Meningitis is the inflammation of the meninges, often caused by infection. It can be bacterial, viral, or fungal in origin.

Common Signs/Symptoms (Sx): Fever, headache, stiff neck, photophobia, nausea, vomiting, altered mental status.
Diagnosis: Lumbar puncture to analyze cerebrospinal fluid (CSF), blood cultures, PCR for pathogen detection.
Treatment: Depends on cause; bacterial meningitis requires urgent antibiotics, viral often supportive care, fungal antifungals.

Comparison of Meningitis Types

Type	Common Pathogens	Symptoms	Treatment
Bacterial	Neisseria meningitidis, Streptococcus pneumoniae, Haemophilus influenzae	Severe, rapid onset	Antibiotics
Viral	Enteroviruses, herpesviruses	Milder, self-limited	Supportive care
Fungal	Cryptococcus neoformans	Chronic, in immunocompromised	Antifungals

Bacterial Meningitis

Hib Meningitis: Caused by Haemophilus influenzae type b. Common in children; prevented by Hib vaccine.
Meningococcal Meningitis: Caused by Neisseria meningitidis. Rapid progression; vaccine available.
Pneumococcal Meningitis: Caused by Streptococcus pneumoniae. Most common in adults; vaccine available.

Fungal Meningitis

Cryptococcosis: Caused by Cryptococcus neoformans. Seen in immunocompromised patients; treated with amphotericin B and flucytosine.

Tetanus

Tetanus is caused by Clostridium tetani, which produces the tetanospasmin toxin.

Mechanism: Tetanospasmin blocks inhibitory neurotransmitter release, causing muscle rigidity and spasms.
Treatment: Antitoxin, antibiotics, supportive care.
Prevention: Vaccination with tetanus toxoid.

Botulism

Botulism is caused by Clostridium botulinum, which produces botulinum toxin.

Mechanism: Botulinum toxin blocks acetylcholine release at neuromuscular junctions, causing flaccid paralysis.
Treatment: Antitoxin, supportive care.
Clinical Applications: Botulinum toxin is used therapeutically for muscle spasms, cosmetic procedures (Botox), and migraine treatment.

Leprosy

Leprosy (Hansen's disease) is caused by Mycobacterium leprae. It affects peripheral nerves and skin, leading to sensory loss and deformities.

Treatment: Multidrug therapy (dapsone, rifampin, clofazimine).
Prevention: Early diagnosis and treatment.

Rabies

Rabies is caused by the rabies virus, transmitted via animal bites.

Classic Rabies: Characterized by hydrophobia, agitation, and paralysis.
Paralytic Rabies: Presents with muscle weakness and paralysis.
Pathogenesis: Virus travels from bite site to CNS, causing encephalitis.
Treatment: Post-exposure prophylaxis with vaccine and immunoglobulin.

Poliomyelitis

Poliomyelitis is caused by the poliovirus. It can lead to paralysis by destroying motor neurons in the spinal cord.

Prevention: Vaccination (IPV and OPV).
Treatment: Supportive care.

Arboviral Encephalitis

Arboviruses are transmitted by arthropods (e.g., mosquitoes) and can cause encephalitis.

Common Symptoms: Fever, headache, confusion, seizures.
West Nile Virus: Can cause severe encephalitis, especially in elderly.
Zika Virus: Associated with microcephaly in newborns and neurological complications.

Prion Diseases

Prion diseases are caused by misfolded proteins (prions) that induce neurodegeneration.

Bovine Spongiform Encephalitis (BSE): "Mad cow disease" in cattle; can be transmitted to humans as variant Creutzfeldt-Jakob disease.
Creutzfeldt-Jakob Disease (CJD): Rapidly progressive dementia and motor dysfunction in humans.

Additional info: Prion diseases are unique in that they are not caused by conventional pathogens (bacteria, viruses, fungi), but by infectious proteins. There is no effective treatment; prevention relies on avoiding contaminated food and medical instruments.