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Neuroscience > Viruses affecting the CNS > Flashcards

Viruses affecting the CNS Flashcards

1
Q

Define the terms neurotropic, neuroinvasive and neurovirulent?

A

Neurotropic: capable of replicating in nerve cells

Neuroinvasive: capable of entering or infecting the CNS

Neurovirulent: capable of causing disease within the CNS

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2
Q

What is myelitis?

A

Inflammation of the spinal cord

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3
Q

What is encephalomyelitis?

A

Inflammation of both the brain and spinal cord

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4
Q

What is the difference between primary viral encephalitis and secondary encephalitis?

A

Primary viral encephalitis (acute viral encephalitis): direct viral infection of spinal cord and brain

Secondary viral encephalitis (post-infectious encephalitis): viral spread to brain as a complication of a current viral infection

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5
Q

Describe the general presentation of viral meningits?

A

Headache

Fever

Neck stiffness

Vomiting

Photophobia

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6
Q

What is the major cause of viral meningitis?

A

Enteroviruses

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7
Q

Describe the causes of viral meningitis, other than enteroviruses?

A

Mumps

Varicell-zoster

Influenza

HIV

Herpes simplex 2 (genital)

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8
Q

Describe the presentation of viral encephalitis?

A

Like meningitis, but followed by:

Personality and behavioural changes

Seizures

Partial paralysis

Hallucinations

Altered levels of consciousness

Coma and death

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9
Q

What is the major cause of viral encephalitis?

A

Herpes simplex virus types 1 and 2

Rabiesvirus

Arboviruses

Enteroviruses

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10
Q

Describe postinfectious encephalomyelitis?

A

Can occur a few days after in fection with measles, chickenpox, rubella or mumps

No virus present

Inflammation and demyelination

Possibly autoimmune (part of virus looks like myelin sheath)

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11
Q

Describe Guillain-Barre syndrome?

A

Acute inflammatory demyelinating disease

Following infection with EBV, CMV, HIV

Results in partial or total paralysis, but most people recover

Does not require active infection

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12
Q

Describe Reye’s syndrome?

A

Occurs post-infection with influenza or chickenpox in children

Cerebral oedema, but no inflammation

Associated with administration of aspirin during initial fever

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13
Q

Give an example of a chronic demyelinating disease?

A

Sub-acute sclerosing panencephalitis (SSPE)

Late sequel to measles infection (reason for vaccine - to avoid this)

Rare, due to measles vaccination

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14
Q

By which mechanisms can viruses access the brain?

A

BBB provides protection against some viruses

If virus enters PNS or ganglia > travel via axon fibres to CNS

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15
Q

Describe how viruses move through the PNS to access the CNS?

A

Carried passively along axons or dendrites

Anterograde or retrograde spread

Can cross synaptic junctions

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16
Q

Why aren’t viruses destroyed by the immune system as they travel through the PNS?

A

Protected from attach by CTL as nerve cells do not have class 1 molecules

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17
Q

Where does viral replication take place in the nervous system? Why?

A

In the body, as this is where protein synthesis takes place

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18
Q

How can the viruses access the CNS, other than via the PNS?

A

Bloodstream (viremia)

Can occur via cerebral blood vessels, choroid plexus or memingeal blood vessels

Olfactory bulb

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19
Q

Describe the various effects that viruses can have once they enter the brain?

A

Directly kill neurons > cause inflamamtory disease

Replicate in non-neuronal cells > cause demyelination

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20
Q

Describe the effect of inflammation on the blood brain barrier?

A

During inflamamtion, lymphocytes, antibodies and other immune effectors can enter (they are normally excluded)

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21
Q

Describe the neuroinvasiveness and neurovirulence of rabiesvirus?

A

High neuroinvasiveness and high neurovirulence

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22
Q

Does rabiesvirus require growth in nerve cells as part of its life cycle?

A

Yes

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23
Q

Describe the morphology of the rabiesvirus?

A

Bullet shpaed

-ve stranded RNA

Helical capsid

Envelope

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24
Q

How does rabiesvirus exit nerve cells?

A

Budding (envelope)

25
Q

Describe the pathogenesis of rabies?

A
26
Q

Describe the symptoms of rabies?

A

Aggression (biting)

Thirst, but muscle spasm and terror upon attempt to drink water

27
Q

Describe the time frame for infection with rabiesvirus?

A

Symptoms anywhere between 40 and 70 days after infection

28
Q

Which is the only disease for which vaccination is helpful after infection?

A

Rabies

60 day window of opportunity to catch virus before it gets to brain and mount immune response

29
Q

Which viruses are alpha herpesviruses?

A

HSV 1 and 2

Varicella-zoster virus

30
Q

Do the alpha herpesviruses require growth in nerve cells as part of their life cycle?

A

Yes

31
Q

Describe the neuroinvasiveness and neurovirulence of alpha herpesviruses?

A

Low neuroinvasiveness

High neurovirulence

32
Q

Describe the morphology of alpha herpesviruses?

A

Large

Linear dsDNA genome

Icosahedral

Envelope

33
Q

How do alpha herpesvirsues enter the body?

A

Via mucosal surfaces

34
Q

When does serious disease occur with alpha herpesviruses?

A

If virus moves from mucosal surface to blood and replicates (then enters brain and spinal cord)

35
Q

Where do latent infections of alpha herpesviruses reside?

A

Sensory and autonomic ganglia

36
Q

How is HSV1 transmitted?

A

Contact with infected saliva

37
Q

Which body parts are usually implicated in primary infections with HSV1?

A

Mouth and/or throat

May be inapparent

Gingivomastitis in children

38
Q

Describe the pathogensis of HSV?

A
39
Q

What is the most dangeorus outocome of HSV infection?

A

Severe sporadic encephalitis

Infects neurons and glia in temporal lobe

40
Q

What is the most common cause of severe sporadic encephalitis?

A

HSV infection

Usually reactivation of latent infection, not a primary infection

41
Q

Describe how HSV is maintained in a latent state?

A

Genome of HSV maintained in an episome coated with histones in ganglia

Maintained in latent state by immune mechanisms (CTLs kill HSV when it pops out)

42
Q

What does HSV express in its latent state?

A

Latency activated mRNA transcripts (LATs)

43
Q

How is varicella-zoster virus spread within the body?

A

During chickenpox - haematogenous spread

Susequently enters nerves to cause vesicular rashes

44
Q

Describe the pathogenesis of chickenpox?

A
45
Q

How can varicella-zoster virus become latent?

A

From the rash, can travel back up to DRG and become latent

46
Q

What is shingles?

A

Reactivation of latent varicella-zoster virus

Painful blisters that follow a dermatome

47
Q

In which population does shingles most commonly occur?

A

Elderly (>55)

When CTL response starts to wane, and infection cannot be kept latent

48
Q

What type of virus is poliovirus?

A

Enterovirus

49
Q

How is poliovirus spread?

A

Faecal-oral spread

50
Q

Does poliovirus require growth in nerve cells as part of its life cycle?

A

No

Occurs as an accident

51
Q

Describe the neuroinvasiveness and neurovirulence of poliovirus?

A

Low neuroinvasiveness

High neurovirulence

52
Q

Describe the morphology of poliovirus?

A

+ve RNA

Icosahedral capsid

NO envelope

53
Q

Describe the effect that poliovirus has on the cells that it infects?

A

Cytocidal virus > kills cells in which it replicates

54
Q

How does poliovirus exit cells?

A

Kills cell that it is in so that it is released

55
Q

Describe the pathogenesis of poliovirus?

A
56
Q

Which cell types does poliovirus target? Why?

A

Anterior horn cells in spinal cord

These cells have receptor that virus can use to replicate

57
Q

Describe the outcome of infection with poliovirus?

A

Total paralysis within hours if it infects CNS

<1% is irreversible

Lower lims affected more than upper limbs > acute flaccid paralysis

If trunk, thorax and abdomen affected > quadriplegia

Mortality rate 5-10% once respiratory muscles immobilised

58
Q

When do epidemics of enterovirus meningitis occur?

A

Summer/autumn

Neuroscience (51 decks)

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