22.4 Viruses afffecting the CNS Flashcards
(27 cards)
What do the terms:
Neurotropic
Neuroinvasive
Neurovirulent
mean?
Neurotropic: can replicate in nerve cells
Neuroinvasive: can enter/infect CNS
Neurovirulent: can cause disease within the NS
What do the terms:
Meningitis Encephalitis Myelitis Encephalomyelitis Primary viral encephalitis Secondary encephalitis
Menigitis: infection of the meninges
Encephalitis: inflammation of the brain
Myelitis: infection of spinal cord
Encephalomyelitis: inflammation of brain/spinal cord
Primary viral encephalitis: viral infection of spinal cord/brain (diffuse/focal)
Secondary encephalitis: (post infectious encephalitis) viral infection complications spreading to brain (via blood usually)
What is the difference between viral meningitis and viral encephalitis?
Viral menigitis: more common, less severe (main cause: enterovirus)
Viral encephalitis: severe, different presentation, (causes: herpes, rabies, entero)
When does postinfectious encephalomyelitis occur?
A few days after (measles, chickenpox, rubella, mumps)
No virus but inflammation/demyelination
Autoimmune??
What is Guillain-Barre syndrome?
Acute inflammatory demyelinating disease following infection (EBV, CMV, HIV)
Partial/total paralysis (most people recover in weeks)
Doesn’t require active infection
What is Reye’s syndrome?
Cerebral oedema (not inflammation)
Associated w/ administration of asprin to treat fever in Flu/V.Z.
What is chronic demyelinating disease?
Rare e.g. 20 years post measles
SPEE
What is AIDS encephalopathy?
Immunodeficiency–> hole in brain (progressive dementia)
How do viruses spread to the brain?
-PNS– via axon fibres–>CNS
nerve fibres don’t have MHC I
In nerves where can viruses replicate?
Body of the nerve (where PRO synthesis occurs)
Which viruses can enter the CNS directly via the bloodstream?
Polio, mumps, measles, coxsackie, HIV (via choroid plexus)
Which viruses can enter via the olfactory bulb?
Herpes simplex, coronavirus
How can viruses cause inflammatory disease in the brain?
- Direct neuron killing
- Replication in oligodendrocytes (demyelination)
- BBB can become permeable
What is the neuroinvasiveness/virulence like in rabies?
High (glycoprotein gets displayed on cell surface)
How does rabies grow?
Growth in nerve cells (obligatory)
Virus entry–>muscle–>peripheral nerves–>CNS–>peripheral nerves–>salivary gland
What type of virus is rabies?
Bullet shaped, -ve RNA, helical capsid/envelope
Rabies in Aus??
Not classical rabies by lyssavirus of bats
What is the neuroinvasiveness/virulence of alpha herpes like?
Low NI, high NV
What viruses are included in the alpha herpesviruses?
Simplex 1 (coldsores), 2 (genital) VZ
Where do the a-herpes viruses normally live?
Muscosal surfaces (reactivation)
Sensory, autonomic ganglia in PNS (latent infection)
What is the pathogenesis of HSV?
Break in skin/membrane, 10-15% show disease–>nerve endings
Rare: severe sporadic encephalitis
What is the latency of HSV?
20% harbour it
Maintained as an episome (LATs expressed–>CD8 kill them)
What is the pathogenesis of VZV?
Chicken pox (varicella)/shingles (zoster)
V: mucosa–>repliation in regional LNs–> hematogenous–>spleen/liver–> 2* viraemia–>nerves/skin rash
Where does VZV live in its latent phase?
Dorsal root ganglion
