how do viruses cause disease in humans?

Question 1

what is the basic reproductive number?

Answer 1

• how many new infections one person will generate during their infectious period

Question 2

what is the name of the system for viral classification?

Answer 2

• baltimore system

- based on viral genetic material

Question 3

what are the problems a virus must solve?

Answer 3

1. what cells to enter and how
2. how to replicate inside cell
3. how to move from one infected cell to another
4. mechanisms to evade host defences

Question 4

what are entry points for a virus?

Answer 4

skin
alimentary tract
urogenital tract
eye

Question 5

what is an example of a virus that remains apical even when it spreads?

Answer 5

flu

Question 6

what is an example of a virus that is basolateral?

Answer 6

• rabies
• is on the basolateral side
• has access to underlying tissue and can spread systematically

Question 7

how can viruses spread haematogenously?

Answer 7

• direct through capillaries
• replicating in endothelial cells
• through vector bite
• through lymphatic capillaries

Question 8

what is viraemia?

Answer 8

• presense f virus in the blood

Question 9

what is a neurotropic virus?

Answer 9

one that infects neural cells

Question 10

what is a neuroinvasive virus?

Answer 10

• can enter CNS following infection of peripheral site

Question 11

what is neurovirulence?

Answer 11

can cause disease of neural tissue

Question 12

which viruses are neurovirulent?

Answer 12

HSV

rabies

Question 13

which viruses are neuroinvasive?

Answer 13

mumps

Question 14

describe how mumps can affect CNS

Answer 14

• it is neuroinvasive so can get into CNS

- but not neurovirulent- so won’t cause much damage when in CNS

Question 15

what 3 things determine viral tropism?

Answer 15

• cell receptors
• cellular proteins that regulate transcription
• cell proteases

Question 16

describe the effect of HSV on CNS

Answer 16

• not neuroinvasive- o won’t get into CNS

- but very neurovirulent, so if it gets n will cause a lot of trouble

Question 17

what are the 2 mechanisms by which influenza evades host immunity?

Answer 17

• antigenic shift

- antigenic drift

Question 18

what is antigenic shift?

Answer 18

the process by which two or more different strains of a virus, or strains of two or more different viruses, combine to form a new subtype

Question 19

what is antigenic drift?

Answer 19

genetic variation in viruses, arising by the accumulation of mutations in the virus genes that code for virus-surface proteins that host antibodies recognize.

Question 20

how can viruses be cytolytic?

Answer 20

• inhibition of host protein synthesis leading to loss of membrane integrity
• syncytium formation
• induction of apoptosis

Question 21

what are non cytocylic ways a virus can injure cells?

Answer 21

• CD8 mediated
• CD4 mediated
• B cell mediated

Question 22

what are 3 mechanisms by which viruses damage cells?

Answer 22

1. cytolytic
2. non cytolytic
3. cell injury due to free radicals

Question 23

routes of viral transmission

Answer 23

resp tract 
skin and mucous membrane 
faecooral 
blood borne 
sexual 
vertical