Lecture 4

Question 1

How have viruses evolved

Answer 1

By different independent routes

Question 2

What do RNA viruses proceed

Answer 2

DNA viruses

Question 3

Why do errors accumulate rapidly with RNA

Answer 3

Not subject to proof reading

Question 4

What are known especially in influenza viruses (2)

Answer 4

1. Antigenic drift

2. Antoigenic shift

Question 5

What is the reason for spontaneous mutations

Answer 5

Error rate of enzymes - in RNA dependent polymerase is much higher than that for DNA dependant polymerase

Question 6

What are Quasispecies

Answer 6

Different isolates of the same species/serotype

Question 7

What is FMDV known for

Answer 7

Mutations and quasispeices

Question 8

The productions of quasi species may assist with?

Answer 8

the virus to persist in the individual host

Question 9

What is antigenic drift?

Answer 9

Viruses will slowly accumulate point mutations

Question 10

What can spontaneous point mutations lead to

Answer 10

Serologically detectable differences - response of the immune system

Question 11

What is antigenic shift?

Answer 11

The dramatic changes which accompany reassortment of viruses with segmented genomes

Question 12

What are viral mutations

Answer 12

Reassortment/antigenic shift

Question 13

What do pigs have receptors for

Answer 13

Both Human and avian viruses

Question 14

Where is gene reassortment important

Answer 14

Segmented viruses

Question 15

What is recombination

Answer 15

A physical interaction of viral genomes in co-infected cells

Question 16

When does recombination occur

Answer 16

When a host cell in infected with two parent viruses

Question 17

When do conditional lethal mutants replicate

Answer 17

Under norma physiological environmental conditions, but not under others

Question 18

When do temperature sensitive mutants replicate

Answer 18

Under normal physiological temperature but stop with Tm changes

Question 19

What does attenuated mutants mean

Answer 19

Lost ability to cause disease in humans/animals

Question 20

Where are attenuation and attenuated mutants used

Answer 20

In vaccines

Question 21

What is a defective virus

Answer 21

A virus will not produce the formation of live, active progeny. This type of infection is called an abortive infection and the reason for this

• The host cell is defective
• The virus itself that is defective and cannot replicate

Question 22

What do defective viruses do

Answer 22

Block adsorption receptors of cells for infective viruses

Question 23

What is pathogenesis

Answer 23

Mechanism of disease development - the process by which a viral infection leads to disease

Question 24

What is pathogenicity

Answer 24

The ability of microorganisms to produce disease in a host

Question 25

What is virulence

Answer 25

the degree of pathogenicity

Question 26

What are the 6 prerequisites for pathogenicity

Answer 26

1. Gain entry to host 2. Colonize 3. Enter the tissues 4. Multiply 5. Resist or interfere with the host's defence mechanisms 6. Cause damage

Question 27

What is essential for viruses to enter a cell

Answer 27

Receptor attachment

Question 28

How can a virus enter (6)

Answer 28

1. Respiratory system 2. Conjunctiva and other mucous membranes 3. Digestive system 4. Urogenital system 5. Mechanical - skin injury 6. Transpacental

Question 29

What are cell receptors for viruses

Answer 29

Attachment sites

Question 30

What are cell transcription factors

Answer 30

Recognise viral promoters and enhancer sequences

Question 31

How is a virus released from host cell (4)

Answer 31

1. Skin 2. Respiratory tract 3. Digestive tract 4. Genital tract, urinary tract, saliva, milk and blood

Question 32

Why do viruses try to evade the host's immune response

Answer 32

To enable them to persistently infect their host

Question 33

What does restricted gene expression mean

Answer 33

Replication only takes place in a limited population of cells

Question 34

What does viral-induced immunosuppression mean

Answer 34

Viruses destroy immunocompetent cells such as machrophages, neutrophils and lymphocytes

Question 35

What is immunological tolerance

Answer 35

In prenatal infections, the infected host may not recognise the foreign virus and therefore, antiviral antibodies are not produced

Question 36

List 5 mechanisms of viral persistence

Answer 36

1. Restricted gene expression 2. Viral-induced immunosupression 3. Immunological toerange 4. Non-immunogenicity 5. Stimulation of the production of non-neutralising antibodies or defective cell mediated immunity

Question 37

What are 4 consequences of persistence

Answer 37

1. Chronic viral infection 2. Slow viral infections 3. Oncogenic viral infections 4. Latent viral infections

Question 38

What is a quasispecies

Answer 38

different isolates of the same species/serotype

Question 39

How does a live virus work

Answer 39

They grow the virus in a different host so it is a weaker strength.

Question 40

Where do most viruses go

Answer 40

Lymph nodes

Question 41

When will viruses leave the blood stream

Answer 41

When they reach a target organ where they do the most damage

Question 42

What is a latent infection

Answer 42

May persist in a specialised group of cells

Question 43

What is immunological tolerance

Answer 43

When the virus crosses the placenta, the virus is seen as self to the immune system so it doesn't pick it up.