Microbial Diseases of the Nervous System

Chapter 22: Microbial Diseases of the Nervous System

Overview of Nervous System

  • Central Nervous System (CNS): Comprises the brain and spinal cord.

  • Peripheral Nervous System (PNS): Consists of nerves branching from the CNS.

Meninges and Cerebrospinal Fluid (CSF)

  • Meninges: Protective layers surrounding the brain and spinal cord.

    • Dura mater: Outer layer.

    • Arachnoid mater: Middle layer.

    • Pia mater: Innermost layer.

  • Blood-Brain Barrier: Protects the CNS from potentially harmful substances.

Microbial Diseases in Focus

  • Case study presents two children with cranial nerve paralysis after consuming canned chili, suggesting potential neurotoxic infections.

Bacterial Diseases of the Nervous System

Learning Objectives

  • Understand meningitis types and their epidemiology.

  • Diagnosis and treatment of bacterial meningitis.

Meningitis

  • Definition: Inflammation of the meninges.

  • Symptoms: Fever, headache, stiff neck, nausea, vomiting, and may lead to convulsions/coma.

  • Bacterial meningitis is more severe compared to viral meningitis, which tends to be milder.

Meningococcal Meningitis

  • Causative Agent: Neisseria meningitidis (aerobic, gram-negative diplococcus).

  • Symptoms: Begins as a throat infection with a potential rash and bacteremia. Notable for ecchymosis.

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

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

Other Bacterial Forms of Meningitis

  1. Haemophilus influenzae type b (Hib): Gram-negative, significant in children ages 6 months to 4 years. Prevented by Hib vaccine.

  2. Streptococcus pneumoniae: Involved in pneumonia and otitis media; high mortality in elderly. Prevented by conjugated vaccine.

Diagnosis and Treatment

  • Diagnosis: Via spinal tap to analyze CSF for bacteria and white blood cell count.

  • Treatment: Initiate broad-spectrum cephalosporins while awaiting results.

Key Bacterial Diseases

Tetanus

  • Causative Agent: Clostridium tetani.

  • Mechanism: Neurotoxin (tetanospasmin) blocks relaxation pathways in muscles, resulting in spasms.

  • Prevention: Vaccination with DTaP; booster required every 10 years.

  • Symptoms: Muscle spasms leading to possible respiratory failure.

  • fewer then 10 cases per year , mortality rate is about 10-20% even with treatment, highlighting the importance of prevention through vaccination.

Botulism

Gram positive bacteria that produces a potent neurotoxin, which can lead to paralysis and respiratory issues.

  • Causative Agent: Clostridium botulinum.

  • Mechanism: Botulin toxin blocks neurotransmitter release, leading to flaccid paralysis.

  • Prevention: Proper food canning practices to avoid toxin contamination.

Leprosy

  • Causative Agent: Mycobacterium leprae.

  • Forms: Tuberculoid (loss of sensation) and lepromatous (disfiguring nodules).

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

Viral Diseases of the Nervous System

Poliomyelitis

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

  • Symptoms: Sore throat, nausea; can lead to paralysis in 1% of cases.

  • Prevention: Salk (inactivated) and Sabin (attenuated) vaccines.

Rabies

  • Causative Agent: Rabies virus, typically transmitted via animal bites.

  • Symptoms: Muscle spasms and hydrophobia.

  • Diagnosis: Direct fluorescent-antibody test.

  • Treatment: Post-exposure vaccine and immune globulin.

Arboviral Encephalitis

  • Key Diseases: Eastern and Western Equine Encephalitis, St. Louis and California Encephalitis, West Nile Virus.

  • Symptoms range from mild to severe; prevention focuses on controlling mosquito populations.

Fungal and Protozoan Diseases

Cryptococcosis

  • Causative Agent: Cryptococcus neoformans; often severe in immunocompromised.

  • Treatment involves antifungals like amphotericin B.

Amoebic Meningoencephalitis

  1. Naegleria fowleri: Infects nasal mucosa, leading to 100% fatal PAM.

  2. Acanthamoeba: Causes GAE.

Prion Diseases

  • Abnormal proteins induce others to misfold, leading to neurodegeneration. Examples include Creutzfeldt-Jakob Disease and Bovine Spongiform Encephalopathy (BSE).

Summary of Important Concepts

  • Understand the differences between bacterial, viral, and protozoan diseases of the nervous system.

  • Know the causative agents, symptoms, and treatment options available for each disease.

  • Recognize prevention strategies for major diseases, especially those that are vaccine-preventable, such as tetanus, rabies, and polio.