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.
Things to revise/add later:
Bibliography: LWW microbiology