WK 10- CNS infections Flashcards
What are the protective mechanisms in place to protect the brain
Blood brain barrier and the blood CSF barrier
What comprises the BBB
BBB is made from a basement membrane, surrounded by a solid endothelium and astrocytes with no gap junction
-prevents movement of solutes from the blood stream into the brain unless accompanied by a transporter
What is the blood CSF comprised of
Blood vessel is surrounded by a thin basement membrane, fenestrated endothelium and choroid plexus epithelium
-fenestrated epithelium allows movement of some particlesq
What are the 3 mechanisms that pathogens use to pass through the protective barrier of the brain
- Grow across
- Passive transcytosis
- Carried in by immune cells ‘trojan horse’
How do microbes grow across into the CNS
microbes can grow in the endothelial cells and then into the astrocytes or choroid plexus (ie polio and meningococus)
What are the ways which microbes can undergo passive transcytosis
- transported across the intracellular vacuoles
- cross between endothelial cells by disrupting tight junctions
- secrete cytotoxic molecules that destroy the cell
- sepsis induced activation of the blood CNS barrier–> systemic release of bacterial components in blood causes release of chemokines and cytokines-> causes direct and indirect activation of the endothelial cells which makes them more permeable
How are microbes carried in through inflammatory cells
infected inflamm cells can migrate into the brain and meninges, lyse and release the organism, or the organisms may pass from cell to cell
How do viruses enter the CNS
- due to small size they can more easily transcytose→ also use leukocyte crossing
- herpes virus use anterograde transport into the brain from the peripheral cell body via olfactory nerve (travel through axonal terminals)
With bacterial meningitis;
- what cells are present
- what happens to the levels of proteins and glucose
- Neutrophils
- Increased Proteins- as bacteria are made of protein
- Decreased glucose-> due to bacteria using glucose as an energy source
- positive gram stain and culture
With viral meningitis;
- what cells are present
- what happens to the levels of proteins and glucose
- Monocytes
- Protein and glucose levels stay the same
How is the CSF analysed in meningitis
•Sample 1: serology; PCR –Viruses •Sample 2: biochemistry –Glucose –Protein •Sample 3: bacteriology –Gram stain –Culture
What is meningitis
Infection of the meninges and CSF
What is encephalitis
Infection of the brain tissue
What is coning
Squeezing of the brain and brainstem through the foramen magnum as a result of swelling -> occurs when there is an increase in intracranial pressure
What are the 3 most common causes of bacterial meningitis
→ haemophilus influenza (formally type b- other serotypes do cause disease but to a lesser extent), Neisseria meningitis, strep pneumonia (most significant)
What gram stain is haemophilus influenzae
Gram negative cocco-bacilli
Why have rates of bacterial meningitis caused by Hib recently decreased
Immunisation-> most children are protected via maternal Ab up until 3 months, then require immunisations
What gram stain is neisseria
gram neg diploccocus
What age group is most often affected by neisseria meningitis
Adolescents-> due to majority of adolescents harbouring the bacteria and being in close spaces-> like university
How can neisseria meningitis cause bacterial meningitis
-transmitted by resp droplets→ enters pharyngeal regions→ move to non-cilliated resp cells and will sit on the surface and can move in and out of the cell→ can then get into membranes and into the blood stream and pass into CSF-> in the blood stream LPS triggers increased vascular permeability and DIC and a cytokine storm and can potentially cause sepitcaemia-> bacteria in the CSF causes swelling of the brain and a rise in intracranial pressure along with potential blood clots and empyema (pus collection)
