Microbial Diseases of the Nervous System: Study Guide

Diseases of the Nervous System

Basic Anatomy of the Nervous System

The nervous system is a complex network responsible for coordinating body activities and transmitting signals between different body parts. It is divided into two main components:

• Central Nervous System (CNS): Consists of the brain and spinal cord. It processes information and coordinates activity throughout the body.

• Peripheral Nervous System (PNS): Comprises all nerves outside the CNS. It connects the CNS to limbs and organs.

Meninges are protective membranes covering the brain and spinal cord. They consist of three layers:

• Dura mater: Outermost, tough layer.

• Arachnoid mater: Middle, web-like layer.

• Pia mater: Innermost, delicate layer adhering to the CNS surface.

Meningitis

Overview and Symptoms

Meningitis is inflammation of the meninges. Common symptoms include:

• Fever

• Headache

• Stiff neck

• Nausea and vomiting

• Photophobia (sensitivity to light)

• Altered mental status

Types of Meningitis

Type	Common Causes	Features	Treatment
Bacterial	Neisseria meningitidis, Streptococcus pneumoniae, Haemophilus influenzae	Severe, rapid onset, high mortality if untreated	Antibiotics, supportive care
Viral	Enteroviruses, herpesviruses	Milder, self-limiting	Supportive care
Fungal	Cryptococcus neoformans	Chronic, often in immunocompromised	Antifungal drugs

Bacterial Meningitis

• Hib (Haemophilus influenzae type b) Meningitis: Common in children; prevented by Hib vaccine.

• Meningococcal Meningitis: Caused by Neisseria meningitidis; outbreaks in close quarters; vaccine available.

• Pneumococcal Meningitis: Caused by Streptococcus pneumoniae; affects young and elderly; vaccine available.

Fungal Meningitis

• Cryptococcosis: Caused by Cryptococcus neoformans; often affects immunocompromised individuals (e.g., HIV/AIDS patients).

Diagnosis and Treatment

• Diagnosis: Lumbar puncture to analyze cerebrospinal fluid (CSF) for cell count, glucose, protein, and microbial culture.

• Treatment: Depends on cause; bacterial forms require prompt antibiotics, viral forms are usually self-limiting, fungal forms require antifungals.

Tetanus

Mechanism of Tetanospasmin Toxin

• Caused by Clostridium tetani, an anaerobic, spore-forming bacterium.

• Tetanospasmin is a neurotoxin that blocks inhibitory neurotransmitter release, leading to uncontrolled muscle contractions (spastic paralysis).

• Prevention: Tetanus toxoid vaccine (part of DTaP/Tdap).

• Treatment: Administration of antitoxin, wound care, and supportive therapy.

Botulism

Mechanism of Botulinum Toxin

• Caused by Clostridium botulinum.

• Botulinum toxin blocks acetylcholine release at neuromuscular junctions, causing flaccid paralysis.

• Symptoms: Double vision, difficulty swallowing, muscle weakness.

• Treatment: Antitoxin administration, supportive care.

Clinical Applications

• Botulinum toxin is used therapeutically in small doses to treat muscle spasms, migraines, and for cosmetic purposes (e.g., Botox).

Leprosy

• Also known as Hansen's disease; caused by Mycobacterium leprae.

• Affects skin, peripheral nerves, mucosa of upper respiratory tract, and eyes.

• Symptoms: Skin lesions, numbness, muscle weakness.

• Treatment: Multi-drug therapy (MDT) with dapsone, rifampin, and clofazimine.

Rabies

Classic vs Paralytic Rabies

• Classic (Furious) Rabies: Hyperactivity, hydrophobia, agitation.

• Paralytic Rabies: Muscle weakness, paralysis, less dramatic symptoms.

Pathogenesis

• Caused by Rabies virus (genus Lyssavirus).

• Transmitted via animal bites; virus travels via peripheral nerves to CNS, causing encephalitis.

• Prevention: Post-exposure prophylaxis (PEP) with rabies vaccine and immunoglobulin.

Poliomyelitis

• Caused by Poliovirus (an enterovirus).

• Transmitted via fecal-oral route.

• Symptoms: Most infections asymptomatic; some develop fever, sore throat, and in rare cases, paralytic disease due to motor neuron destruction.

• Prevention: Inactivated polio vaccine (IPV) and oral polio vaccine (OPV).

Arboviral Encephalitis

Overview and Symptoms

• Encephalitis is inflammation of the brain, often caused by arboviruses (arthropod-borne viruses).

• Common symptoms: Fever, headache, confusion, seizures, and sometimes coma.

West Nile Virus

• Transmitted by mosquitoes; birds are primary hosts.

• Most infections are asymptomatic; some develop fever, and a small percentage develop neuroinvasive disease (encephalitis or meningitis).

Zika Virus

• Transmitted by Aedes mosquitoes.

• Symptoms: Fever, rash, joint pain, conjunctivitis.

• Complications: Congenital Zika syndrome (microcephaly in infants born to infected mothers).

Prion Diseases

• Caused by abnormal, infectious proteins called prions that induce misfolding of normal proteins in the brain.

Disease	Host	Features
Bovine Spongiform Encephalopathy (BSE)	Cattle	"Mad cow disease"; progressive neurodegeneration
Creutzfeldt-Jakob Disease (CJD)	Humans	Rapidly progressive dementia, motor dysfunction, fatal

Additional info: Prion diseases are unique in that they do not involve nucleic acids and are resistant to standard sterilization procedures.