Viruses

Question 1

What is a neurotropic virus?

Answer 1

Capable of replicating in the nerve cells

Question 2

What is a neuroinvasive virus?

Answer 2

Capable of entering or infecting the CNS

Question 3

What is a neurovirulent virus?

Answer 3

Capable of causing disease within the nervous system

Question 4

What is viral encephalitis?

Answer 4

Serious viral disease, presents like meningitis but then get personality and behavioural changes, seizures, partial paralysis, altered levels of consciousness and ultimately coma and death. Mostly caused by herpes simplex virus types 1 and 2

Question 5

What is postinfectious encephalomyelitis?

Answer 5

No virus present in the brain, but inflammation and demyelination. Can occur a few days after infections such as measles, chickenpox, rubella or mumps

Question 6

What is Guillain-Barre syndrome?

Answer 6

Acute inflammatory demyelinating disease following infection

Question 7

How can viruses spread to the brain?

Answer 7

• Travel via axon fibres of the peripheral nerves to the CNS
• Replication of viruses takes place in the body of nerves
• Other viruses enter the CNS directly via the blood stream
• Others can enter via the olfactory bulb

Question 8

What is normally excluded from the BBB but can enter during inflammation?

Answer 8

Lymphocytes, antibodies and other immune effectors

Question 9

Describe Rabiesvirus and its pathogenesis

Answer 9

HIGH neuroinvasiveness and HIGH neurovirulence

• growth in nerve cells is an obligatory part of the life cycle
• bite bypasses skin to muscle, undergoes a little bit of replication and then gets into the nerves –> spinal cord –> brain, replicating all the way
• people become more aggressive and thirsty due to changes in the brain and behaviour but muscle spasms and terror upon attempt to drink water

Question 10

Why does the Rabies vaccine work?

Answer 10

Once the virus gets to the CNS = death, BUT it can take up to 60 days
- vaccine works because the time taken for the immune response to develop to clear the virus is less than the virus needs to complete its full damage

Question 11

What is the neuroinvasiveness and neurovirulence of HSV?

Answer 11

LOW neuroinvasiveness and HIGH neurovirulence

Question 12

Describe the pathogenesis of HSV1

Answer 12

The virus enters the body through contact with infected saliva

• often get inapparent infection
• or can get a latent infection

Question 13

Describe the pathogenesis of varicella-zoster virus

Answer 13

• During chickenpox the viral spread is hematogenous (by the blood), but then enters the nerves from the resulting vesicular rash
• ALSO has the capacity to go to the dorsal root ganglia and become latent –> can be reactivated, and if so follows a dermatome

Question 14

Describe Poliovirus and its pathogenesis

Answer 14

Growth in nerve cells is NOT an obligatory part of the life cycle of the virus

• LOW neuroinvasiveness and HIGH neurovirulence
• cytocidal virus –> kills cells in which it replicates
• target motor neurons in the anterior horn –> paralysis
• • if it invades the CNS can cause total paralysis within hours