CNS Infections What structures make up the central nervous system (CNS)?

What structures make up the central nervous system (CNS)?

The brain, spinal cord, and cranial nerves.

What protects the CNS?

Bone (skull, vertebral column) and membrane layers (meninges).

How can microbes enter the CNS through the bloodstream?

By crossing the blood–brain barrier to cause encephalitis or crossing the CSF barrier to cause meningitis.

What are three ways microbes can cross the blood–brain barrier (BBB)?

1. Growing across or infecting BBB cells (cells that comprise the barrier)

2. Being passively transported in intracellular vacuoles

3. Being carried across by infected white blood cells

How do cells typically appear in septic/purulent (bacterial) meningitis?

Very high; predominantly neutrophils

How does protein typically appear in septic/purulent (bacterial) meningitis?

Markedly elevated (highest of all meningitis types; because of bacterial protein).

How does glucose typically appear in septic/purulent (bacterial) meningitis?

Low (bacteria consume glucose + impaired transport).

How do cells typically appear in aseptic (viral or non-bacterial) meningitis?

Moderately elevated; mainly lymphocytes/mononuclear cells.

How does protein typically appear in aseptic meningitis?

Slightly to moderately elevated, but not as high as bacterial.

How does glucose typically appear in aseptic meningitis?

Usually normal.

Which major bacterial meningitis pathogens have a capsule as a key virulence factor?

Neisseria meningitidis, Haemophilus influenzae type b, and Streptococcus pneumoniae.

Which pathogens produce IgA protease to help colonize mucosal surfaces?

Neisseria meningitidis, Haemophilus influenzae, and Streptococcus pneumoniae.

Which meningitis pathogen uses pili for attachment to the nasopharynx?

Neisseria meningitidis.

Which bacterial meningitis pathogens produce endotoxin (LPS or LPS-like)?

Neisseria meningitidis and Haemophilus influenzae (both are Gram-negative).

How do Haemophilus influenzae pili compare to Neisseria meningitidis pili?

Both mediate adherence to the nasopharyngeal epithelium, but Neisseria pili are a major virulence factor with antigenic variation and a stronger role in invasion, while Haemophilus pili mainly aid colonization and are less central to virulence.

What organisms cause meningitis in neonates (<1 month)?

Group B Streptococcus (S. agalactiae), E. coli, Listeria monocytogenes.

What organisms cause meningitis in infants (1–23 months)?

Haemophilus influenzae, Streptococcus pneumoniae, Neisseria meningitidis, Streptococcus agalactiae (group B), E.coli

What organisms cause meningitis in children (>2 years) and adults?

Streptococcus pneumoniae, Neisseria meningitidis.

• we start building immunity which is why there are less pathogens

What organisms cause meningitis in older adults (>65 years)?

Streptococcus pneumoniae, Neisseria meningitidis, Listeria monocytogenes, aerobic Gram-negative bacilli.

• Listeria affects where most susceptible; neonates and older adults

• We often see underlying conditions in older adults v

What increases risk of Neisseria meningitidis infection?

Lack of antibodies to capsular antigens, C5–C9 complement deficiency (MAC complex), crowding (dorms, barracks), and exposure during winter/early spring.

What is the incubation period and typical presentation of meningococcal disease?

Incubation 1–3 days; sudden onset of headache, sore throat, fever, stiff neck, drowsiness, and hemorrhagic rash (indicating septicemia)

What is the mortality of untreated vs. treated meningococcal meningitis?

100% untreated; ~10% with treatment.

Which meningococcal vaccines are used?

Polysaccharide (MPSV4) and conjugate (MCV4) covering A, C, Y, W-135.

• MCV4 for 11 to 55 y/o

What lab diagnosis is used

gram stain of CSF, culture, white cell counts

• note that lab diagnosis is essential for

How many serotypes does Haemophilus influenzae have, and what are they based on?

Six serotypes (a–f), based on their capsules.

Which serotype of Haemophilus influenzae most commonly causes meningitis?

Type b (Hib).

Where is Haemophilus influenzae normally found?

It is a resident of the respiratory tract of infants and children.

Why are infants protected from Hib early in life, and when does this protection drop?

Maternal antibodies protect infants until about 3–4 months → after this, antibodies wane, creating a “window of susceptibility.”

What is the incubation period of Hib meningitis?

About 5–6 days.

How severe is Hib meningitis compared with meningococcal or pneumococcal meningitis?

It is less fatal than meningococcal and pneumococcal meningitis.

What long-term complications can occur after Hib meningitis?

Hearing loss, delayed language development, intellectual disabili, and seizures.

What vaccine protects against Hib?

The Hib vaccine (given starting at >2 months of age).

Is Streptococcus pneumoniae a common cause of meningitis?

Yes — it’s listed as a common cause.

What important structural feature of S. pneumoniae is emphasized on the slide?

It is encapsulated.

Where is S. pneumoniae commonly carried?

In the throats of many healthy people.

How often does S. pneumoniae invade the blood and meninges?

Invasion of blood and meninges is rare.

Which immune factor increases susceptibility to invasive disease?

Low levels of capsular antibodies (antibodies are type-specific).

How many capsule types does the slide say S. pneumoniae has?

Over 85 capsule types.

How does pneumococcal meningitis mortality compare to Hib and meningococcal disease?

Higher mortality than Hib and meningococcus

What vaccines are listed on the slide?

Heptavalent protein-conjugate (for 2–23 months and immunocompromised) and 23-valent (for children >5 years).

Which pathogen causes acute onset meningitis in 6–24 hours with skin rash?

Neisseria meningitidis.

Which pathogen most commonly affects children <5 years old?

Haemophilus influenzae.

Which pathogen commonly affects all ages but especially children <2 and the elderly?

Streptococcus pneumoniae.

Which meningitis pathogen has the highest mortality rate in treated cases?

Streptococcus pneumoniae (20–30%).

Which pathogens have the lowest rates of major CNS sequelae?

Neisseria meningitidis (<1%) and Haemophilus influenzae (9%).

What is a common sequela seen in up to 10% of survivors of bacterial meningitis?

Deafness

Which type of meningitis is most common overall?

Viral meningitis.

How does viral meningitis typically compare in severity to bacterial meningitis?

It is milder.

What are common symptoms of viral meningitis?

Headache, fever, and light sensitivity (photophobia).

What is the usual outcome of viral meningitis?

Complete recovery.

Why is diagnosis of viral meningitis difficult by culture?

Viruses are difficult to isolate from CSF.

What test is commonly used to diagnose viral meningitis?

PCR to detect viral genome.

What virus family often causes viral meningitis?

Enteroviruses

• typically in GI tract but if it gets into blood then able to cause meningitis

What is encephalitis?

Inflammation of the brain parenchyma.

What is the usual cause of encephalitis?

Viruses

What type of dysfunction is typical in encephalitis?

Cerebral dysfunction.

What symptoms are associated with encephalitis?

Abnormal behavior, seizures, nausea, vomiting, fever.

What is the most common cause of encephalitis?

Herpes simplex virus (HSV).

How do neonates usually acquire HSV encephalitis?

From passage through a birth canal shedding HSV-2.

What causes HSV encephalitis in older children and adults?

Reactivation of HSV-1 in trigeminal ganglia spreading to the temporal lobe.

• rare

What is the fatality rate of untreated HSV encephalitis?

About 70% if not treated.

What is the treatment for HSV encephalitis?

Antiviral therapy for 21 days.

Was poliovirus once a common cause of encephalitis?

Yes, formerly.

What are the early symptoms of poliovirus infection?

1–4 days of fever, sore throat, malaise → followed by meningitis-like signs.

What neuronal cells does poliovirus target, and what results

Motor neurons → paralysis.

What major factor reduced polio encephalitis?

Vaccination since the 1950s and global eradication efforts.

What animals are involved in the West Nile virus cycle?

Birds and culicine mosquitoes.

What are humans and horses considered in WNV infection?

Incidental hosts.

How did WNV spread in North America?

Migration of infected birds.

How is West Nile virus diagnosed?

Detection of WNV RNA or IgM antibodies in serum/CSF.

Is there a vaccine for WNV?

No; control focuses on mosquitoes.

What neurological diseases have been suggested to have viral origins?

MS, Parkinson’s, schizophrenia, and senile dementia.

What normally limits spread of infection into the CNS?

The blood–brain barrier (BBB).

Once pathogens cross the BBB, what diseases can they cause?

Meningitis (meninges) or encephalitis (brain tissue).

What is the most common type of meningitis?

Viral meningitis.

Besides infections, what else can cause CNS disease?

Bacterial toxins.