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Introduction to Microbiology

• Title: Microbiology with Diseases by Body System

• Chapter: 20

• Author: Robert W. Bauman

• Edition: Third Edition

• Focus: Microbial Diseases of the Nervous System and Eyes

• Prepared by: Mindy Miller-Kittrell, North Carolina State University

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Anatomy Review of the Nervous System

• Parts of the Nervous System:

  • Central Nervous System (CNS)

  • Peripheral Nervous System (PNS)

• Central Nervous System Components:

  • Cerebrum: Responsible for voluntary muscle control, perception, and thinking.

  • Cerebellum: Involved in involuntary body movements.

  • Brain Stem: Controls breathing, heart rate, and blood pressure.

  • Spinal Cord: Connects the brain to the body.

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Lumbar Puncture

• Purpose: Collection of cerebrospinal fluid (CSF)

• Procedure Location: Between Lumbar Vertebrae L3 and L4

• Components:

  • Spinous Process

  • Needle

  • Spinal Cord

  • Cerebrospinal Fluid (CSF)

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Anatomy Review: Peripheral Nervous System (PNS)

• Functions: Nerves transfer commands from CNS to muscles and glands.

• Nerve Types:

  • Sensory Nerves: Carry sensory input to the CNS.

  • Motor Nerves: Deliver commands from the CNS to muscles.

  • Mixed Nerves: Contain both sensory and motor fibers.

• Cells:

  • Neuroglia: Support and protect neurons.

  • Neurons: Primary signaling cells.

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Portals of Infection of the CNS

• Characteristics of CNS:

  • Axenic (germ-free) environment with no normal microbiota.

• Ways Pathogens Access CNS:

  • Breaks in bones and meninges.

  • Medical procedures.

  • Travel through peripheral neurons (e.g., rabies).

  • Infect cells of the meninges (e.g., causing meningitis).

• Disease Mechanisms:

  • Directly infect nervous system cells (e.g., meningitis).

  • Release toxins affecting neurons (e.g., botulism, tetanus).

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Bacterial Meningitis

• Signs and Symptoms:

  • Sudden high fever and severe meningeal inflammation.

  • Possible encephalitis leading to behavioral changes, coma, and death.

  • Rapid development of symptoms.

• Key Pathogens:

  1. Streptococcus pneumoniae: Gram-positive diplococci.

  2. Neisseria meningitidis: Gram-negative diplococci.

  3. Haemophilus influenzae: Gram-negative pleomorphic rods.

  4. Listeria monocytogenes: Gram-positive rods, foodborne.

  5. Streptococcus agalactiae (Group B strep): Gram-positive cocci.

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Bacterial Meningitis: Pathogenesis and Epidemiology

• Pathogenesis:

  • S. agalactiae: Acquired during birth; leading cause of meningitis in newborns.

  • Listeria monocytogenes: Obtained through contaminated food (dangerous for pregnant women).

• Epidemiological Insights:

  • S. pneumoniae: Present in 75% of human throats; not spread by casual contact.

  • Meningococcal meningitis: Potentially epidemic.

• Diagnosis, Treatment, and Prevention:

  • Diagnosed based on symptoms and CSF culture.

  • Treated with intravenous antimicrobial drugs.

  • Vaccines available for S. pneumoniae, H. influenzae type b, and N. meningitidis.

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Bacterial Meningitis: Top Three Pathogens

• Characteristics: All bacteria that cause meningitis are encapsulated and transmitted through respiratory droplets.

  1. Streptococcus pneumoniae: Gram positive diplococci; affects very young and old.

  2. Neisseria meningitidis: Gram negative diplococci; linked to epidemic meningitis among college freshmen.

  3. Haemophilus influenzae: Gram negative pleomorphic rods; vaccination has reduced disease prevalence in young children.

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Figure 20.3 Cells of Streptococcus pneumoniae

• Type: Scanning Electron Microscopy (SEM)

• Size: 2 μm

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Figure 20.4 Pleomorphic Bacilli of Haemophilus influenzae

• Type: Light Microscopy (LM)

• Size: 20 μm

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Botulism (Flaccid Paralysis)

• Signs and Symptoms:

  • Caused by intoxication from pre-formed toxins in food; spores germinate under anaerobic conditions.

  • Three forms: foodborne, infant, and wound botulism.

• Pathogen and Virulence:

  • Clostridium botulinum: Causative agent; different strains produce various neurotoxins.

• Epidemiology:

  • Approximately 50 cases per year in the U.S.; most cases of infant botulism.

  • Honey should not be fed to infants.

• Diagnosis, Treatment, and Prevention:

  • Treatment approaches: intestinal tract washing, botulism immune globulin, antimicrobial drugs.

  • Prevention through destruction of spores in contaminated foods.

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Figure 20.7 Botulism Toxin Overview

• Mechanism: Toxin blocks release of excitatory neurotransmitters at neuromuscular junctions.

• Comparison:

  • (a) Normal neuromuscular junction.

  • (b) Neuromuscular junction affected by botulism toxin.

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Tetanus

• Signs and Symptoms:

  • Characterized by lockjaw and muscle spasms spreading to other muscles.

• Causative Agent:

  • Clostridium tetani: Spores grow in deep wounds, producing neurotoxin tetanospasmin.

• Pathogenesis and Epidemiology:

  • Infection through breaks in skin or mucous membranes; incubation period depends on distance from CNS.

  • Mortality rate ~50% if untreated.

• Diagnosis, Treatment, and Prevention:

  • Diagnosed by characteristic symptoms; treated with immunotherapy and vaccines.

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Figure 20.9 Tetanus Toxin Overview

• Mechanism: Tetanospasmin blocks release of inhibitory neurotransmitters.

• Comparison:

  • (a) Normal neurotransmitter action.

  • (b) Effect of tetanospasmin resulting in constant muscle contraction.

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Viral Diseases of the Nervous System

• Characteristics:

  • Viruses more readily cross the blood-brain barrier.

  • More frequent than bacterial and fungal infections.

• Examples: Meningitis, polio, rabies, and encephalitis.

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Viral Meningitis

• Characteristics: Less severe than bacterial meningitis.

• Signs and Symptoms: Similar to bacterial meningitis but usually milder.

• Pathogens: 90% cases caused by viruses in the genus Enterovirus.

• Epidemiology and Diagnosis:

  • More common than bacterial meningitis; spreads via respiratory droplets and feces.

  • Diagnosed by signs and absence of bacteria in CSF; no specific treatment.

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Poliomyelitis

• Signs and Symptoms:

  • Asymptomatic in 90% of cases.

  • Minor polio: nonspecific symptoms.

  • Nonparalytic polio: muscle spasms, back pain.

  • Paralytic polio (1% cases): paralysis; post-polio syndrome.

• Causative Agent: Poliovirus; transmitted through contaminated water.

• Vaccine: Successful vaccination efforts have significantly reduced incidence.

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Rabies (Rhabdoviruses)

• Signs and Symptoms: Characteristic neurological signs if virus reaches CNS.

• Pathogen: Rabies virus; often transmitted via bites or scratches from infected animals.

• Pathogenesis: Virus replicates in muscle cells, moves to neurons, and reaches brain.

• Epidemiology: Zoonotic disease with significant public health implications.

• Diagnosis, Treatment, and Prevention:

  • Diagnosed through unique symptoms or postmortem detection of Negri bodies.

  • Treatment includes immunoglobulin and vaccinations.

  • Prevention through controlling rabies in pets.

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Figure 20.12 Predominant Wildlife Reservoirs for Rabies in the U.S.

• Reservoir Species: Skunk, fox, raccoon.

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Arboviral Encephalitis

• Characteristics: Arboviruses are transmitted by blood-sucking arthropods like mosquitoes.

• Symptoms: Usually mild, cold-like symptoms; severe if they cross the blood-brain barrier.

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Figure 20.15 Transmission of Arboviral Encephalitis Viruses

• Vectors: Mosquitoes transmitting diseases from birds to humans.

• Hosts: Various mammals and birds, with specific hosts for different viruses.

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Table 20.2 Characteristics of Arboviral Encephalitis Diseases in the U.S.

• Viruses and Features: Overview of diseases such as Eastern equine encephalitis, St. Louis encephalitis, and West Nile encephalitis, including transmission vectors and natural hosts.

• Human Cases: Incidence and associated mortality rates categorized by virus and environment.

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Mycoses of the Nervous System

• Definition: Mycoses are fungal diseases that may spread from the lungs to the CNS via blood.

• Symptoms: Mushroom toxins can cause neurological problems and hallucinations.

• Complications: May result in fungal meningitis.

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Protozoan Infections of the Nervous System

• Characteristics:

  • Rare infections usually caused by two types of organisms:

    • African sleeping sickness

    • Meningoencephalitis

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African Sleeping Sickness

• Diagnosis and Treatment: Microscopic observation of trypanosomes; treatment depends on disease stage.

• Prevention: Application of insecticides to reduce occurrence.

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Prion Diseases

• Definition: Prions are infectious proteins associated with spongiform encephalopathies like scrapie and mad cow disease.

• Effect: Causes brain degeneration, leaving holes in tissue.

• Transmission: Humans may contract from consuming infected cattle meat.

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Variant Creutzfeldt-Jakob Disease (V-CJD)

• Signs and Symptoms: Insomnia, weight loss, memory failure; progressive loss of muscle control.

• Pathogen: Caused by an abnormal prion form; latency can be extensive.

• Diagnosis and Treatment: Diagnosed based on symptoms; often confused with dementia; no available treatment; prevention relies on avoiding prion-ridden meat.