Neisseria Meningitidis

Characteristics/Epidemiology

Nasopharyngeal mucosa - asymptomatic carrier or causing disease

Human is the only natural host.

Incidence highest in <1 y.o. infants.

Pathogenesis/Transmission

Transmission - respiratory droplets

Risk factors

• Recent viral or mycoplasma upper respiratory infection
• Active or passive smoking
• Complement deficiency

 

1. Pili

Allows attachment

2. Polysaccharide capsule

• Antiphagocytic
• Antigenic
• Most important virulent factor
• More than 14 types (serogroups)
  -> A, B, C, W, Y cause 90% of meningococcal disease
  * B - leading endemic cause, then C
  * A - cause of epidemic in developing countries

3. Lipooligosaccharide

• LOS is released after autolysis and cell division
  -> causes toxic effects in disseminated disease

4. Outer membrane proteins (OMPs)

OMP and LOS determines the serotypes (not serogroups).

5. IgA protease

 

Clinical significance

1. Meningitis

• Haemophilus influenzae used to be the leading cause until vaccination
• N. meningitidis is now the leading cause
• Symptoms:
  * Joint pain
  * Petechial rash
  * Fever, malaise
  * Severe headache, rigid neck, vomiting, photophobia
• Can cause coma and death in a few hours.

2. Septicaemia

• In 30% of meningitis patient can have fulminant septicaemia.
• Severe shock (due to endotoxin, i.e. LOS)
• In very young children, can cause Waterhouse-Friderichsen syndrome:
  * Large blotchy purple skin haemorrhage
  * Vomiting and diarrhoea
  * Shock
  * Necrosis of adrenal gland
• Can cause death <12 hours.

Laboratory identification

Microscopy

• Piliated, nonmotile
• Pair of kidney bean
• Encapsulated (unlike N. gonorrhoea)

Culture

• Prompt plating due to sensitivity to heat and drying
• Plain chocolate agar with increase CO2 if CSF/blood
• Selective chocolate agar (Thayer-Martin medium) if other samples

Others

• Ferments both glucose and maltose
• CSF need to be centrifuged first to concentrate for microscopy
• CSF may also show decreased glucose, increased protein, and neutrophil
• Latex agglutination using serogroup-specific anticapsular antibody

Treatment

First line: Penicillin G/ampicillin (both can pass blood-brain barrier)
Second line: cefotaxime or ceftriaxone if penicillin resistance a concern.

Prevention/immunity

Vaccination

Capsular vaccine for serogroup A, C, W, Y -> very effective.

Capsular B (most common endemic cause) -> does not elicit effective immune response -> no vaccine

Prophylaxis

Rifampicin to treat family members -> eliminate carrier state.

 

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Things to revise/add later:

Bibliography: LWW microbiology

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