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Microbiology and Immunology 2500A/B Lecture Notes - Cerebrospinal Fluid, Arachnoid Mater, Pia Mater

Microbiology and Immunology
Course Code

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Meningitis Feb. 25, 2013
Ending with ‘itis’ usually refers to inflammation
Meningitis is an inflammation/infection of the meninges
It is usually due to a viral or a bacterial infection
Viral meningitis tends to be less severe than bacterial meningitis and can usually be resolved
with a specific treatment
While on the other hand, bacterial meningitis can be extremely severe (very dangerous)
Meninges they are the membranes that envelop the central nervous system (CNS) which
includes the brain and the spinal cord
This includes: dura mater, arachnoid mater & pia mater
Dura mater Closest to the skull (thicker layer)
Arachnoid mater between dura mater & pia mater
Pia mater Closest to the brain (thin, delicate membrane)
Between the arachnoid and pia maters contains a little space which is filled by the
cerebral spinal fluid
Blood Brain Barrier (BBB) it is a protective cellular structure that restricts the passage of
chemicals, toxins and microorganisms from the blood to the CNS
Blue dye is injected to an animal
The animal is sacrificed to see the organs (liver, pancreas, kidneys) turn blue; however the
brain did not turn blue
So the blue dye was then injected into the cerebral spinal fluid causing the brain to turn
blue, but the rest of the organs did not This is due to the blood brain barrier
Astrocyte Provides the support for the blood
Endothelial cells It forms tight junctions to
prevent foreign substances from getting through
Due to the BBB, the CNS is known to be an
“immune privileged” site (Ex. Testicles, eyes,
There is no inflammation at these sites
because it would simple damage its own tissue
As mentioned before, the astrocytes
provide support for other cells of the CNS including
the BBB
The endothelial cells are bounded together
by structures called the “tight junctions”
There are no white blood cells or antibodies present in the CNS, but it does contain microglia
cells, which are the ‘tissue macrophages’ of the CNS
The Disease: Bacterial Meningitis (Steps)
1) Bacterial meningitis live in the nasopharynx (nasopharyngeal colonization)
2) An event occurs where the bacteria invades epithelial layer and gains access to the blood
3) The bacteria multiplies in the blood (counter our immune system)
4) It then crosses the BBB
5) By crossing the BBB, it is able to invade the meninges and CNS
6) It also increases the permeability of the BBB causing more bacteria to crossover and invade
7) This will lead to severe inflammation
8) Results in edema, increased cranial pressure and leukocyte migration
9) Proinflammatory cytokines are produced from the white blood cells
10) All these processes cause neuronal damage
This disease is rare but also dangerous; capable to killing in days
Early signs may be non-specific
Generally in an outbreak, the people who are infected by the disease first are most likely to die
People are generally more wary of the initial symptoms if the outbreak is known to be occurring
Mortality rate is still around (10-25%)
Even the individuals who have survived have irreversible neurological damage
resulting in permanent brain damage, blindness, hearing loss and learning
Symptoms in Children & Adults
High Fever**
Severe Headache**
Vomiting or Nausea
Confusion or Difficulty concentrating** in the very young, this may appear is inability to
maintain eye contact
Sleepiness or difficulty waking up
Stiff Neck**
Sensitivity to light (photophobia)
Lack of interest in drinking and eating
Skin rashes in cases of meningococcal meningitis
**95% of the patients will have atleast two of these symptoms; major symptoms
Symptoms in Infants
Constant crying
Excessive sleepiness or irritability
Poor feeding
A bulge in the soft spot on top of the baby’s head (fontanel)
Stiffness in the baby’s body and neck
Skin rash in the cases of meningococcal meningitis
Risk Factors
o Lack of vaccination
o People who are in the age of 15 months to 25 years old
o Living in a community setting (Crammed settings)
University students living in dormitories
Military personnel
Boarding schools
Childcare facilities
o Disease can also result in immunocompromised individuals due to disease or chemotherapy
o Also in individuals who have gone through cranial surgery
There are blood tests done to locate inflammatory markers
But the major diagnostic tool is the lumbar puncture (spinal tap)
A needle is inserted in between the 3rd & 4th lumbar vertebrae to extract fluid from
That fluid is then examined: gram stain & culture, presence of white cells and low
Then there is also imaging (CT or MRI)
Nucal Rigidity The individual is unable to flex their head forward
Brudzinski’s sign The neck stiffness is so severe that it causes the patient’s knees to flex up
when the neck is flexed
Kernig’s sign When the hip is flexed to a 90 degrees, the patient is unable to straighten their
leg due to severe stiffness of the hamstrings
It should be treated immediately
The patient must begin intravenous antibiotics before the cerebral spinal fluid can be examined
for culture analysis