Microbial Infections of the Nervous System: Disease Snapshots

Microbial Infections of the Nervous System

Rabies

Rabies is a viral infection of the nervous system, primarily transmitted through animal bites. It is a significant zoonotic disease with fatal outcomes if untreated.

• Causative agent: Rabies virus (enveloped, single-stranded RNA virus, Rhabdoviridae family)

• Epidemiology: 3–5 human cases per year in the U.S.; 55,000 deaths worldwide annually, mostly in Africa and Asia

• Transmission & prevention: Zoonosis, contracted via infected animal bite or by breathing aerosolized virus; most common animal source is wild animals such as bats, raccoons, and skunks. Vaccination is recommended for animal handlers and travelers to high-risk areas.

• Signs & symptoms: Fever, headache, discomfort, hydrophobia, fear of water, excessive salivation

• Pathogenesis & virulence factors: Virus replicates in muscle cells, then travels to the CNS, causing encephalitis and death

• Diagnosis & treatment: Diagnosis involves direct fluorescent antibody test after a human bite. Treatment includes wound cleaning, rabies immunoglobulin, and vaccination.

Arboviral Encephalitis: West Nile and La Crosse

Arboviral encephalitis is caused by viruses transmitted by arthropods, such as mosquitoes. West Nile and La Crosse viruses are notable causes in the United States.

• Causative agent: West Nile virus (enveloped, single-stranded RNA virus, Flaviviridae family); La Crosse virus (Bunyaviridae family)

• Epidemiology: Around 1,200 cases of encephalitis annually in the U.S.; La Crosse cases mainly in the Midwest

• Transmission & prevention: Zoonosis via mosquito bites; prevention includes mosquito control and avoiding bites

• Signs & symptoms: Fever, headache, flu-like symptoms, neurological symptoms

• Pathogenesis & virulence factors: Virus replicates in the CNS, causing inflammation and encephalitis

• Diagnosis & treatment: Many antibody-based tests available; treatment is supportive

Meningococcal Meningitis

Meningococcal meningitis is a bacterial infection of the meninges, caused by Neisseria meningitidis. It is highly contagious and can cause outbreaks, especially in close-contact settings.

• Causative agent: Neisseria meningitidis (Gram-negative bacterium)

• Epidemiology: Most common in young adults; potential for outbreaks; incubation period 3–4 days

• Transmission & prevention: Transmitted via respiratory droplets; prevention includes vaccination

• Signs & symptoms: Fever, chills, delirium, stiff neck, photophobia, sensitivity to light

• Pathogenesis & virulence factors: Capsule resists phagocytosis; endotoxin causes inflammation

• Diagnosis & treatment: Gram stain and culture of CSF; antibiotics required

Pneumococcal Meningitis

Pneumococcal meningitis is caused by Streptococcus pneumoniae, a Gram-positive bacterium. It is a major cause of bacterial meningitis in children and adults.

• Causative agent: Streptococcus pneumoniae (Gram-positive bacterium)

• Epidemiology: 3,000–6,000 cases per year in the U.S.; mostly affects unvaccinated people under two or over 65 years of age

• Transmission & prevention: Person-to-person transmission; vaccination recommended

• Signs & symptoms: Fever, chills, headache, confusion, agitation, vomiting

• Pathogenesis & virulence factors: Capsule resists phagocytosis; inflammation damages CNS

• Diagnosis & treatment: Gram stain and culture of CSF; antigen-based tests; antibiotics required

Listeria Meningitis (Listeriosis)

Listeriosis is a bacterial infection caused by Listeria monocytogenes, often affecting immunocompromised individuals and pregnant women.

• Causative agent: Listeria monocytogenes (Gram-positive bacterium)

• Epidemiology: 1,000 cases with 200 deaths annually in the U.S.; high risk for pregnant women

• Transmission & prevention: Contaminated food; prevention includes proper food handling

• Signs & symptoms: Fever, headache, stiff neck, confusion, agitation

• Pathogenesis & virulence factors: Intracellular growth; resists phagocytosis

• Diagnosis & treatment: Culture from blood or CSF; antibiotics required

Botulism

Botulism is a neuroparalytic disease caused by the toxin produced by Clostridium botulinum. It can occur via foodborne, wound, or infant botulism.

• Causative agent: Clostridium botulinum (Gram-positive bacterium)

• Epidemiology: About 100 cases annually in the U.S.; most cases are infant botulism

• Transmission & prevention: Not contagious; foodborne botulism from improperly canned foods; prevention includes proper food handling

• Signs & symptoms: Flaccid paralysis, blurry vision, difficulty swallowing, dry mouth

• Pathogenesis & virulence factors: Botulinum toxin blocks acetylcholine release, causing paralysis

• Diagnosis & treatment: Identification of toxin in serum/stool; antitoxin and supportive care

Cryptococcosis

Cryptococcosis is a fungal infection of the CNS, caused by Cryptococcus neoformans and C. gattii. It is most common in immunocompromised patients.

• Causative agent: Cryptococcus neoformans and C. gattii (fungi)

• Epidemiology: Over 1 million cases annually worldwide; mostly in immunocompromised individuals

• Transmission & prevention: Fungal spores inhaled from bird droppings; no effective prevention

• Signs & symptoms: Cough, flu-like symptoms, fever, headache, agitation, disorientation

• Pathogenesis & virulence factors: Polysaccharide capsule resists phagocytosis; infects CNS

• Diagnosis & treatment: Culture and microscopy; antifungal drugs required

Toxoplasmosis

Toxoplasmosis is a protozoan infection caused by Toxoplasma gondii. It is widespread and can cause severe disease in immunocompromised individuals and pregnant women.

• Causative agent: Toxoplasma gondii (protozoan)

• Epidemiology: Up to 23% of U.S. population exposed; severe disease in immunocompromised and pregnant women

• Transmission & prevention: Ingestion of contaminated food/water; prevention includes proper food handling and avoiding cat feces

• Signs & symptoms: Healthy people often asymptomatic; severe disease includes fever, confusion, neurological symptoms

• Pathogenesis & virulence factors: Intracellular growth; evades immune response

• Diagnosis & treatment: ELISA or PCR for diagnosis; antiparasitic drugs required

Human Transmissible Spongiform Encephalopathy (Prion Diseases)

Prion diseases are rare, fatal neurodegenerative disorders caused by misfolded proteins (prions). They include Creutzfeldt-Jakob disease (CJD) and variant CJD (vCJD).

• Causative agent: Prions (misfolded proteins)

• Epidemiology: Median age of death is 68 years for CJD; vCJD affects younger individuals; incubation can be years to decades

• Transmission & prevention: vCJD transmitted via contaminated medical procedures or ingestion of infected tissue; prevention is difficult

• Signs & symptoms: Personality changes, memory loss, mental decline, problems with movement

• Pathogenesis & virulence factors: Prions cause misfolding of normal proteins, leading to neurodegeneration

• Diagnosis & treatment: No treatment available; diagnosis via MRI, EEG, and brain biopsy

Additional info:

• These diseases illustrate the diversity of microbial and non-microbial agents (viruses, bacteria, fungi, protozoa, prions) that can infect the nervous system.

• Diagnosis often relies on laboratory tests, including culture, microscopy, serology, and molecular methods.

• Prevention strategies include vaccination, proper food handling, and avoiding exposure to vectors or contaminated materials.