Nervous System Infections Study Notes 26

Nervous System Infections

• General Overview

  • Infections affecting the nervous system can severely impair functions such as movement, sensation, and cognition.

  • Historical stigma associated with conditions like leprosy has led to social isolation of affected individuals.

• Types of Infections

  • Poliomyelitis:

  • Can cause paralysis or respiratory failure requiring mechanical assistance.

  • Hansen’s Disease (Leprosy):

  • Associated with severe physical deformities, historically causing social ostracism.

  • Can result in loss of digits or facial deformity.

  • CNS Infections:

  • Rare but can lead to hearing loss or disability, especially in children.

  • Before antibiotics, these infections were often fatal.

Anatomy, Physiology, and Ecology

• Neuron Structure and Function:

  • Each neuron has several regions:

  • Dendrites: Branching projections that receive signals.

  • Cell Body: Contains the nucleus and is the command center.

  • Axon: Long structure that transmits signals to other neurons or cells.

  • Neurons communicate via:** neurotransmitters** released from synaptic vesicles at the axon terminal, which cross the synapse to transmit signals to the next neuron.

• Central Nervous System (CNS):

  • Comprising the brain and spinal cord, it is encased in protective bone.

  • It has a complex structure where different parts perform specialized functions.

  • Infections can lead to inflammation known as encephalitis.

• Peripheral Nervous System (PNS):

  • Composed of nerves and ganglia connecting the CNS to limbs and organs.

  • Includes:

  • Motor Neurons: Transmit signals from the CNS to muscles.

  • Sensory Neurons: Carry sensory information to the CNS.

• Protection Mechanisms:

  • CNS is shielded by meninges (three protective membranes):

  • Dura Mater: Tough outer layer.

  • Arachnoid Mater: Middle layer containing cerebrospinal fluid (CSF).

  • Pia Mater: Delicate innermost layer.

  • CSF plays a critical role in cushioning the brain and spinal cord and is a sterile environment under normal conditions.

Bacterial Diseases of the Nervous System

• Meningitis:

  • Most common form of infectious disease of the CNS involves the meninges.

  • Symptoms include initial cold-like symptoms escalating to severe headache, neck stiffness, vomiting, and can rapidly lead to death if untreated.

  • Major bacterial pathogens include:

  • Streptococcus pneumoniae

  • Neisseria meningitidis

  • Haemophilus influenzae

• Pneumococcal Meningitis:

  • Symptoms range from cold-like symptoms to severe complications including deafness and potentially rapid death.

  • Caused by Streptococcus pneumoniae; emphasizes the need for vaccination.

• Meningococcal Meningitis:

  • Characterized by petechiae (purplish skin spots) and potential for endotoxic shock.

  • Caused by Neisseria meningitidis; outbreaks can occur in crowded conditions.

  • Vaccination is crucial for prevention; several serotypes exist.

Botulism

• Overview and Pathogenesis:

  • Caused by the neurotoxin produced by Clostridium botulinum; can lead to flaccid paralysis affecting respiratory muscles.

  • Toxin can be ingested through contaminated food, impacting nerve cell communication and leading to muscle paralysis.

• Treatment:

  • Intravenous antitoxin is administered to neutralize circulating toxin.

  • Supportive care is often needed, as recovery from nerve damage can take weeks.

Viral Diseases of the Nervous System

• Rabies:

  • Symptoms include fever, confusion, hallucinations, paralysis, and ultimately respiratory failure if untreated.

  • The rabies virus (part of the rhabdovirus family) is transmitted via the saliva of infected animals.

  • Post-exposure prophylaxis includes immediate wound cleaning and vaccination.

  • Once symptoms appear, treatment options are very limited, with a high fatality rate.

Summary of Key Points

• CNS infections can severely impact human health.

• Important understanding of anatomy and types of neuro-infectious diseases is crucial for diagnosis and treatment.

• Preventive measures, including vaccination, are critical to control and prevent outbreaks of diseases like meningitis and rabies.

• Knowledge of pathogenesis aids in formulating treatment plans.

Microorganisms Gain Entrance to the Central Nervous System

Microorganisms can gain entrance to the central nervous system (CNS) through several pathways:

1. Hematogenous Spread: Pathogens can enter the bloodstream and breach the blood-brain barrier (BBB), leading to CNS infections.

2. Direct Entry: This can occur via trauma or surgery, where pathogens gain direct access to the CNS.

3. Retrograde Axonal Transport: Some viruses (e.g., rabies) can travel along nerves to reach the CNS.

4. Infection of Adjacent Structures: Infections in nearby tissues can spread to the CNS, such as sinusitis leading to meningitis.

Importance of the Blood-Brain Barrier

The blood-brain barrier is a selective permeability barrier that protects the CNS from toxins and pathogens while regulating the passage of substances. Its importance in the treatment of infections of the CNS includes:

• Prevention: The BBB prevents many microbes and chemicals from reaching the CNS, which complicates infections but protects the brain.

• Treatment Implications: Many antibiotics cannot cross the BBB effectively, necessitating alternate treatment strategies such as high-dose medications or therapeutic approaches that disrupt the barrier temporarily to allow drug access.

Bacterial Diseases of the Nervous System

Botulism

• Characteristics: A rare but potentially fatal illness caused by a neurotoxin from Clostridium botulinum.

• Symptoms: Include flaccid paralysis, weakness, and respiratory failure.

• Causes: Ingestion of food contaminated with the botulinum toxin.

• Pathogenesis: The toxin interferes with signal transmission between nerves and muscles.

• Modes of Transmission: Primarily via contaminated food; wound botulism occurs through infected wounds.

• Prevention: Proper food preservation and preparation methods.

• Treatment: Intravenous antitoxin and supportive care.

Pneumococcal Meningitis

• Characteristics: A bacterial form of meningitis caused by Streptococcus pneumoniae.

• Symptoms: Cold-like symptoms progressing to severe headache, neck stiffness, potential deafness, and can lead to death if untreated.

• Causes: Typically occurs following respiratory infections.

• Pathogenesis: Bacteria invade the CNS and cause inflammation of the meninges.

• Modes of Transmission: Respiratory droplets from an infected person.

• Prevention: Vaccination and early treatment of respiratory infections.

• Treatment: Prompt administration of antibiotics is critical to reduce morbidity and mortality.

Meningococcal Meningitis

• Characteristics: Caused by Neisseria meningitidis, associated with outbreaks in crowded environments.

• Symptoms: Symptoms include fever, headache, a rash of petechiae, and neck stiffness.

• Causes: Infection typically arises from respiratory droplets.

• Pathogenesis: The infection leads to inflammation of the meninges and can cause endotoxic shock.

• Modes of Transmission: Close contact with infected individuals, particularly in confined spaces.

• Prevention: Vaccines available for several serotypes; prophylactic antibiotics for close contacts of infected persons.

• Treatment: Immediate antibiotic therapy; managing shock and supportive care.

Viral Diseases of the Nervous System

Rabies

• Characteristics: Caused by the rabies virus, part of the Rhabdoviridae family.

• Symptoms: Initial symptoms include fever, confusion, and hallucinations, progressing to paralysis and eventually respiratory failure.

• Causes: Transmitted via the saliva of infected animals.

• Pathogenesis: The virus travels from the site of entry to the CNS via retrograde axonal transport.

• Epidemiology: Occurs worldwide, with higher risks in areas with uncontrolled rabies in animals.

• Prevention: Vaccination of at-risk animals and immediate cleaning of wounds after potential exposure.

• Treatment: Limited post-symptom treatment options; immediate post-exposure prophylaxis with rabies vaccine and immunoglobulin vastly improves outcomes.