Lecture 2: Infections of the Central Nervous System Flashcards
(48 cards)
Where does the cerebral spinal fluid act as a shock absorber?
Between the pia mater and arachnoid
(circulating around the brain and spinal cord)
What are the 3 connective tissues surrounding the brain?
Pia mater
Arachnoid
Dura mater
What is meningitis classified by?
Inflammation of the connective tissue layers surrounding the brain
What are capillaries throughout the body made of?
Endothelial cells
In the brain where are the endothelial cells packed more tightly together to produce tight junctions?
Sub arachnoid and perivascular space
What is known as the blood-brain barrier?
Sub arachnoid and perivascular space
What substances can pass the blood-brain barrier?
Lipid solubility - oxygen, carbon dioxide, ethanol, steroid hormones
Specific transport systems - sugars, amino acid
Why does the brain loose the arm of the immune response?
Antibodies are too large to cross the blood-brain barrier
Many antibodies are unable to pass the barrier due to their size
What are the common human flora associated with meningitis?
Streptococcus pneumoniae
Haemophilus influenzae
Neisseria meningitidis
What are all the bacteria associated with meningitis?
Streptococcus pneumoniae
Haemophilus influenzae
Neisseria meningitidis
Escherichia coli
Streptococcus agalactiae
Listeria monocytogenes
Staphylococcus aureus
What are the pathogenic and host factors associated with meningitis?
Bacterial pathogenic factors:
Capsule - polysaccharide capsule
Adhesins - stick to endothelial surface
Host factors:
Cytokines
Selectins on endothelial surface
Integrins on neutrophils
How does bacterial invasion of meningitis occur to the cerebral spinal fluid (CSF)?
Bacteria adhere to capillary wall and enter CSF in low numbers
Local macrophages are stimulated by bacterial breakdown products and TNF and IL-I are produced
(fragments released = cytokine production)
TNF and IL-I initiate expression of selectin molecules on the endothelial cell surface.
Endothelial cell IL-8 causes neutrophils to express integrins
Neutrophils adhere to endothelium and enter CSF - breakdown of blood-brain barrier allows entry of albumin
CSF now contains bacteria, neutrophils and protein in significant quantities
What can pneumococci do to allow entry through the pharynx?
Pneumococci can switch capsule production on/ off
Makes it difficult for the pathogen to adhere
What does IL-I do in bacterial invasion of meningitis in the CSF?
Initiates expression on endothelial cells
What does IL-8 do in bacterial invasion of meningitis in the CSF?
They drive the expression of integrins on neutrophils
What does integrin do in bacterial invasion of meningitis in the CSF?
Causes cell-to-cell adhesion
How is a brain abscess diagnosed?
Fever
Headache
Vomiting
Photophobia
Rash
Abnormal behaviour
How is a brain abscess diagnosed?
(4 ways)
Lumbar puncture (needle into spine to extract for dialysis)
Computed tomography (generates 3D image from large series of 2D x-ray images)
Microbiologically - analysis of pus of CSF by microscope
Biochemistry - 3 samples of CSF
How is a brain abscess caused?
Infection of the brain tissue
Inflammatory response over several days forming abscess
Zone of swelling compressing the brain
How is a brain abscess diagnosed through biochemistry?
3 samples of CSF collected:
Protein analysis
Glucose determination
Microbiology
What are the distinguishing features of tuberculous?
Increased WCC
90% monocytes/ lymphocytes
Very high protein
Decreased glucose
What are the distinguishing features of viral meningitis?
Increased WCC (lower than bacterial)
95% lymphocytes
Protein: normal or increased
Glucose: normal
What are the distinguishing features of bacterial meningitis?
WCC - very very high
95% neutrophils
Protein increased
Glucose - massive decrease
What the basic parameters of WCC, protein & glucose in the blood?
WCC: <5/uL
Protein: <450 mg/L
Glucose: >40% blood
