circulation, blood barrier and infection

Question 1

describe how microbial pathogens can damage the nervous system

Answer 1

invasion and replication in the tissues
- direct invasion of peripheral nerves
- from adjacent structures such as from the meninges
- from the blood hematogenous

inducing an immune response:
- inflammation of the CNS
- damage caused by local inflammation to the CNS
- auto immune response

releasing toxins
- block signalling
- damage specific cells

Question 2

describe how pathogens access and spread to the CNS

Answer 2

for every neuron there is a blood vessel => risk of microbes moving from the blood to the nerve cells

Question 3

what are the essential features of the blood brain barrier

Answer 3

• endothelial cells form a tight barrier between the blood and CNS tissue
• the tight junctions stop paracellular flux
• pinocytosis allows transfer of material from blood to brain
• P-glycoprotein pumps actively eject undesired substances

CNS maintained sterile

Question 4

what are the 3 ways microbes can breach the blood brain barrier

Answer 4

transcellular invasion
- pathogens bind host cells and invade through the cell
- this can be passive or active on the part of the pathogen
- ex.: streptococci, Listeria sp., candida, cryptococcus

paracellular invasion
- the tight junctions must dramatically change or new routes open
- increeased pinocytic activity leading to trans-endothelial channels formation or tight junction function can be broken
- ex.: nipah virus, borrelia burgodorferi (lyme)

intracellular within leucocytes
- requires primary infection
- will spread where virus migrates to
- may be hidden to antibodies once established (if spreads cell to cell)
- ex: SIV/HIV and canine distemper

Question 5

what are the indicators of neurological infection

Answer 5

pathology
- inflammation/accumulation of leukocytes
- possibly cellular pathology

clinical signs
- depression
- pyrexia
- cervical pain
- hyperaesthesia
- photophobia
- generalized rigidity
- seizures
- paralysis local and general
- ataxia
- papilloedema
- possible ophthalmic inflammation
- systemic signs: septic shock and crachycardia

Question 6

what are the parameters for normal CSF smaples

Answer 6

• colourless
• less than 6 white blood cells per ul
• total red blood cell count = 0
• few monocytes and lymphocytes, rarely neutrophils
• cisternal total protein less than 0.3 g/l, lumbar less than 0.45 g/l
• specific gravity around 1.007