CNS Infection Flashcards
what age group is most likely to get meningitis
young children
if someone was to get meningitis, who are the most likely to die from it
the elderly
what is aseptic meningitis
bacterial meningitis that is culture negative + and meningitis caused by things other than bacteria
what are the three bacteria that are the commonest causes of meningitis and what is THE most common
H. influenza N. Meningitidis - most common S. pneumoniae
Which type of meningitis is the most prevalent throughout the world
A
why do certain bacteria over others tend to cause meningitis
because they are encapsulated and therefore can avoid complement fixation and phagocytosis by the immune system
which additional bacteria are neonates exposed to that can cause meningitis
E coli and other gram negatives (group B strep and Listeria)
what is the likely source of the bacteria causing menigitis
commensals of the nasopharynx
what is the typical clinical presentation of an child/adult with meningitis
fever, vomiting/nausea, headache, stiff neck, photophobia, seizures
what is the typical clinical presentation of a baby with meningitis
fever, nausea/vomiting, irritable, refusing to feed, altered mental state, bulging fontanelle
when do you get the non-blanching rash associated with meningitis
when you have meningococcal septicaemia
what is the defining sign for meningitis
abnormal CSF
what are the differences between CSF in viral and bacterial meningitis
viral - 100s of LYMPHOCYTES, with negative grain stain, lower amount of protein and higher glucose bacterial - 1000s of NEUTROPHILS, with gram stain positive, higher protein and lower glucose
major contraindications for lumbar puncture
raised ICP shock extensive purpura convolutions coagulation abnormalities
why is it important for CSF analysis to occur quickly after the sample has been taken
because the WBCs start to lyse as they are in hypotonic solution
what is the empiric antibiotic treatment for meningitis in infants, children and adults
intravenous 3rd generation cephalosporin
what is the empiric antibiotic treatment for meningitis in neonates
E coli and other gram negatives - 3rd generation cephalosporin group B streptococcus and Listeria = intravenous penicillin and gentomycin
what is the most common sequalae of bacterial meningitis
hearing loss
what is the most common cause of encephalitis
viral: HSV
what is the fundamental difference in the clinical presentation of meningitis and encephalitis
encephalitis - you have altered conscious state
what are the normal values of CSF
pressure less than 150mmH20 protein less than 0.4g/l WBC less than 5x10^6 no RBC gram stain negative glucose more than 60% blood
difference between neurotropic and neuroinvasive virus
neurotropic - able to replicate in nerve cells neuroinvasive - capable of entering or infecting the CNS
main causes of viral encephalitis
HSV 1 and 2 rabies virus arboviruses enteroviruses
what do we think postinfectious encephalomyelitis is caused buy
autoimmunity - parts of the virus look like parts of the myelin sheath of nerves and therefore the immune system starts to degrade myelin sheath of nerves after a viral infection
common viruses that cause Guillain-Barré syndrome
EBV CMV HIV
What is Reye’s syndrome
post-infectious influenza or chickenpox causing cerebral edema but no inflammation
what are the ways in which viruses can enter the CNS
- by entering peripheral nerves/ganglia and then travelling via axon fibres up to the CNS - via the blood (meningeal BVs, cerebral BVs, coroplexus) - via the olfactory bulb
how are viruses protected when replicating in neurons
they are protected by attack from Cytotoxic T cells as neurons do not express MHC class 1 molecule
where does the viral replication actually occur in the PNS/CNS
in the cell body of the neuron
which viruses can enter the CNS via the olfactory bulb
coronavirus HSV
which viruses can enter the CNS via the blood stream
poliovirus, mumps, measles, coxsackievirus, HIV in monocytes
which viruses can enter the CNS via peripheral nerves
rabies yellow fever HSV 1 and 2
describe the structure of the rabies virus
bullet shaped -ve stranded RNA - helical capsid - envelope
how does rabies virus cause neuronal damage
replication of the virus involves glycoproteins being displayed on the cell surface (for budding) –> immune system recognises these and destroys the cell
mechanism of rabies pathogenesis
rabid animal bites you –> virus from the saliva gets into the myocytes at the bite wound and eventually find the peripheral nerve innervating the muscle –> up the spinal cord –> brain –> salivary glands
signs of rabies infection
aggression thirst
what is the one special thing about rabies virus
it is the only virus that you can vaccinate for after infection (up to 12 days)
explain the neuroinvasiveness and neurovirulence of: - rabies virus - HSV 1 - poliovirus
rabies - both high HSV 1 - low neuroinvasiveness and high neurovirulence poliovirus - low neuroinvasiveness and high neurovirulence
explain the structure of HSV 1
linear dsDNA genome icosahedral envelope
explain the pathogenesis of HSV 1
primary infection of the mucosal surface –> latent phase –> reactivated
how can HSV cause encephalomyelitis
if when reactivated from the latent stage it enters the blood –> replicated up in the liver and spleen –> spinal cord –> CNS Or when reactivated from the latent stage is migrates the wrong way and migrates straight into the spinal cord (most common)
what is the structure of the HSV1 virus when it is latent in the body
maintained as an episome coated with histones
structure of poliovirus
+Ve stranded RNA virus icosahedral capsid no envelope
how does poliovirus cause CNS effects
ingested replicates in gut associated lymphoid tissue enters regional lymph nodes enters blood enters BBB enters spinal cord (replicates in the anterior horn cells causing cell destruction and paralysis)
which enteroviruses can cause enterovirus meningitis
all coxsackie B types coxsackie A7 coxsackie A9 many echoviruses
