Infections of the Nervous System and Sensory Structures

Infections of the Nervous System and Sensory Structures

Overview

The nervous system and sensory structures can be affected by a variety of infectious agents, including bacteria, viruses, fungi, protozoa, and prions. These infections can lead to serious and sometimes fatal diseases, often requiring prompt diagnosis and treatment to prevent permanent neurological damage.

Bacterial Infections of the Nervous System

Bacterial Meningitis

Bacterial meningitis is an acute inflammation of the protective membranes (meninges) covering the brain and spinal cord. It is less common but more severe than viral meningitis due to the production of bacterial toxins.

• Symptoms: Nausea, vomiting, fever, headache, stiff neck, confusion, sleepiness, light sensitivity, convulsions, and coma.

• Diagnosis and Treatment: Early diagnosis and treatment with intravenous antibiotics are essential to prevent permanent neurological damage.

Main Bacterial Causes of Meningitis

Type	Causative Agent	Transmission	Prevention/Treatment
Meningococcal Meningitis	Neisseria meningitidis	Person-to-person, respiratory droplets	Antibiotic therapy, vaccination
Haemophilus influenzae Meningitis	Haemophilus influenzae	Respiratory droplets	Vaccination, antibiotics
Pneumococcal Meningitis	Streptococcus pneumoniae	Carried in throat, respiratory droplets	Conjugated vaccine, antibiotics
Listeria Meningitis	Listeria monocytogenes	Contaminated food	Antibiotics, food safety

Tetanus

Tetanus is an acute, often fatal illness characterized by prolonged contraction of skeletal muscles, leading to rigidity and convulsive spasms.

• Causative Agent: Clostridium tetani (produces neurotoxin)

• Transmission: Spores enter the body through wounds, even minor scratches.

• Prevention: Vaccination (tetanus toxoid)

• Treatment: Administration of antitoxin, antibiotics, and supportive care

Botulism

Botulism is a rare but serious illness caused by Clostridium botulinum, which produces a potent neurotoxin.

• Types: Foodborne, infant, wound, inhalation

• Symptoms: Flaccid paralysis, respiratory failure

• Treatment: Antitoxin, supportive care

Leprosy (Hansen’s Disease)

Leprosy is a chronic, slowly progressive disease caused by Mycobacterium leprae.

• Affected Areas: Skin, peripheral nerves (especially hands and feet), mucous membranes

• Transmission: Likely via respiratory droplets, close contact

• Treatment: Multi-drug antibiotic therapy

Bacterial Diseases of the Eye and Ear

Conjunctivitis (Pink Eye)

Conjunctivitis is the inflammation or infection of the transparent membrane lining the eyelid and part of the eyeball.

• Causes: Bacteria (e.g., Haemophilus influenzae), viruses, allergies, chemicals, foreign objects

• Symptoms: Redness, itchiness, discharge, tearing

• Treatment: Antibiotic drops or ointment (for bacterial causes), good hygiene

Neonatal Gonorrheal Ophthalmia

• Causative Agent: Neisseria gonorrhoeae

• Transmission: During passage through birth canal

• Prevention: Prophylactic antibiotic treatment of newborn's eyes

Trachoma

• Causative Agent: Chlamydia trachomatis

• Symptoms: Damage to eyelids and cornea, potential vision loss

• Treatment: Antibiotic ointments

Otitis Media and Externa (Ear Infections)

• Causes: Various bacteria, often following viral infection

• Symptoms: Ear pain, pressure, possible rupture of tympanic membrane

• Treatment: Pain medication, antibiotics, surgery if severe

Viral Infections of the Nervous System

Viral Meningitis

Also called aseptic meningitis, viral meningitis is generally less severe than bacterial forms.

• Transmission: Direct contact with infected feces or respiratory secretions; mosquitoes can be vectors

• Symptoms: Fever, headache, stiff neck, tiredness, rash, sore throat, vomiting

• Treatment: Supportive care; immune system usually resolves infection

Poliomyelitis (Polio)

• Causative Agent: Poliovirus (nonenveloped, mRNA virus)

• Transmission: Oral-fecal route

• Symptoms: Most cases asymptomatic; mild infection in 4-8%; severe cases can cause paralysis

• Prevention: Inactivated polio vaccine (IPV)

Rabies

• Causative Agent: Rabies virus

• Transmission: Saliva from infected animals (bites)

• Symptoms: Fatigue, muscle aches, anxiety, agitation, insomnia, headache, nausea, vomiting, abdominal pain

• Prevention: Pre- and post-exposure vaccination

Arboviral Encephalitis

Encephalitis caused by arboviruses transmitted by mosquitoes or ticks.

Type	Transmission	Symptoms	Prevention/Treatment
Eastern Equine Encephalitis	Mosquito bite	Fever, headache, irritability, drowsiness, high mortality	No vaccine, supportive care
Western Equine Encephalitis	Mosquito bite	Range from mild to fatal	No vaccine, supportive care
St. Louis Encephalitis	Mosquito bite	Fever, headache, variable fatality	No vaccine, supportive care
La Crosse Encephalitis	Mosquito bite	Mild to severe (seizures, coma)	No vaccine, supportive care
West Nile Encephalitis	Mosquito bite	Rash, headache, fever, neurological symptoms in <1%	Supportive care

Progressive Multifocal Leukoencephalopathy (PML)

• Causative Agent: Polyomavirus JC

• Risk: Immunocompromised individuals

• Symptoms: Inflammation and demyelination in CNS

• Treatment: Increase immune function; drugs have high toxicity

Fungal Infections of the Nervous System

Cryptococcosis

• Causative Agent: Cryptococcus neoformans

• Transmission: Inhalation of spores from soil contaminated with bird droppings

• Forms: Cutaneous, pulmonary, or cryptococcal meningitis

Protozoan Infections of the Nervous System

Cerebral Toxoplasmosis

• Causative Agent: Toxoplasma gondii

• Transmission: Oral (undercooked meat), transplacental

• Symptoms: Often asymptomatic; severe in immunocompromised (speech difficulties, seizures, confusion)

African Trypanosomiasis (Sleeping Sickness)

• Causative Agent: Trypanosoma brucei

• Transmission: Tsetse fly bite

• Symptoms: Coma, meningitis, encephalitis

American Trypanosomiasis (Chagas’ Disease)

• Causative Agent: Trypanosoma cruzi

• Transmission: Bite of reduviid ("kissing bug")

• Symptoms: May produce granulomas in CNS

Prion-Associated Diseases

Overview of Prion Diseases

Prion diseases (transmissible spongiform encephalopathies, TSEs) are rare, infectious, fatal, and progressive neurodegenerative diseases caused by abnormally folded proteins (prions).

• Incubation: Long (years)

• Symptoms: Memory and personality changes, dementia, movement disorders

Human Prion Diseases

Disease	Features	Treatment
Creutzfeldt-Jakob Disease (CJD)	Rare, fatal, degenerative brain disorder	Symptomatic relief only
Variant CJD (vCJD)	Affects younger people, longer duration	Symptomatic relief only
Gerstmann-Sträussler-Scheinker Syndrome (GSSS)	Genetic, amyloid plaques in brain	None
Fatal Familial Insomnia	Sleep disturbance, mental/motor decline	None
Kuru	Endemic in Papua New Guinea, linked to cannibalism	None

Animal Prion Diseases

• Bovine spongiform encephalopathy ("mad cow disease")

• Chronic wasting disease (deer, elk)

• Scrapie (sheep, goats)

• Transmissible mink encephalopathy

• Feline spongiform encephalopathy

• Ungulate spongiform encephalopathy

Summary Table: Major Infectious Agents of the Nervous System

Agent Type	Example Diseases	Key Features
Bacteria	Meningitis, tetanus, botulism, leprosy	Often severe, treatable with antibiotics
Viruses	Polio, rabies, viral meningitis, encephalitis	Variable severity, often supportive care
Fungi	Cryptococcosis	Rare, affects immunocompromised
Protozoa	Toxoplasmosis, trypanosomiasis	Severe in immunocompromised, vector-borne
Prions	CJD, vCJD, GSSS, Kuru	Progressive, fatal, no cure

Key Terms

• Meninges: Three protective membranes covering the brain and spinal cord

• Neurotoxin: A toxin that acts on the nervous system

• Encephalitis: Inflammation of the brain

• Prion: Infectious protein causing neurodegenerative disease

Additional info:

• Vaccination is a key preventive measure for many of these diseases (e.g., meningitis, polio, tetanus).

• Prompt medical attention is critical for suspected CNS infections to reduce morbidity and mortality.