Bacterial Meningitis Flashcards
What is meningitis?
Acute inflammation of the meninges around the brain typically as a result of an infective cause originating (usually) in the blood
- Bacterial
- Fungal
- Viral
- Aseptic? (no discernable cause)
What does the BBB do
Its a specialist structure of endothelial cells within the blood suppl of the cns which prevent entry of bacteria and toxins into the cns
What is the meninges?
A protective membrane found under the skull and around the brain.
The meninges is made up of the dura, the arachnoid and the Pia Mater
How common is bacterial meningitis
Annual incidence (developed countries): 2-5 / 100,000 population
2011/12
1355 (57.4%) meningococcal
340 (14.4%) pneumococcal meningitis
2017/18
755 cases meningococcal disease
(is on the decline)
Which bacterial organism causes meningococcal meningitis
Neisseria meningitidis
What are the characteristics of Neisseria meningitidis
Gram negative diplococcus - unusual
Inhabitant of nasopharynx
Serology based on capsular polysaccharide used to avoid the host immune system, excess outer membrane protein which will illicit immune response away from the bacterial cell and LPS
Causative agent of meningococcal meningitis
How do we differentiate between the at least 12 types of NM
Divided based on distinct capsular groups
At least 12 types identified
B, C, W, Y most common in UK (historically)
A, B, C account for 90% disease on global scale
However, the importance of the capsular groups is always shifting due to vaccination strategies
Is NM only found in ill patients?
No, Nm resides in the URT of healthy individuals
How does NM colonise the host
Nasopharyngeal carriage (10-25% of people do)
Age - a major factor
Behaviour (e.g.) key age group is students
Population
Transmission via aerosol droplets
Nasopharyngeal colonisation
represents a significant challenge
Mucociliary pathway - capsule prevents it being caught in it
Nitric oxide
Colonisation resistance
Lactoferrin
Who is most likely to carry meningococcal bacterium
Late teens, early 20s. Increases up to this point from childhood and decreases afer this point
Vhich virulence factors does NM use to adhere to host cells
Carridge in the healthy host occurs before infection. To cause disease the capsule expression is down regulated and the pilli expression is increased (it may also create a biofilm)
In some cases Nm enters the blood. How does it survive?
Survival in blood is dependant on the presence of certain virulence factors
A critical virulence factor for survival in the blood is the expression of a polysaccharide capsule
Most Nm Capsules inhibit opsonophagocytosis through charge (they repel host immune response cells (phagocytes))
Capsule serotype B mimics host so evades the immune response (identical to NCAM) - it doesn’t work through charge repulsion
What is the issue of Nm colonising the blood
Eventual host cell damage following immune system activation (Blebbing of cell wall - triggers the immune response in areas away from the viable cell)
Uncontrolled growth in the blood may lead to meningococcal septicaemia
What happens to allow NM to move across the BBB
Presence of bacteria in the host blood supply (surviving in it’s capsule) leads to adherence to brain endothelial cells required for BBB crossing (pili). This leads to tight junction depletion and paracellular movement of the bacteria may occur
CNS injury results from endotoxin production and host inflammatory response following migration of PMNs across BBB
Infection of meninges by Nm is meningococcal meningitis
What are the key symptoms of meningitis
Non blanching rash due to damage to capilliaries (not always present)
stiff neck
altered mental state (confusion, delirium, impaired conciousness)
bulging fontanelle (only relevent in <2y)
photophobia (not seen in meningococcal septicaemia)
