Control programmes

Question 1

What are the three ways of controlling an outbreak?

Answer 1

Case numbers (per time or total), eradication, impact

Question 2

What should you aim for Re to be below?

Answer 2

1

Question 3

How many people must be vaccinated to reach herd immunity?

Answer 3

1 - (1/R0)

Question 4

What can happen if vaccination is even only partially infective?

Answer 4

Less susceptible people being exposed, latent period increased so less people infectious, infectious period may be reduced

Question 5

What three factors does the rate of new infection depend on?

Answer 5

The number susceptible, the number infectious, the number of susceptible becoming exposed

Question 6

How can you minimise the number of infectious?

Answer 6

Vaccinate, diagnose early, isolate, cull, treat, quarantine

Question 7

Hoe can you reduce the number of susceptible becoming exposed?

Answer 7

Reduce contact rates, biosecurity, imperfect vaccine reduces secretion

Question 8

What were four methods of controlling FMD?

Answer 8

Diagnose early, stop mixing, cull, trace contacts

Question 9

What happens to the number needed to be culled if you cull immediately?

Answer 9

Half

Question 10

Which kind of vaccination is traditional in an outbreak?

Answer 10

Ring

Question 11

How big must the vaccination ring be?

Answer 11

9km

Question 12

Which type of farms are most susceptible to outbreaks?

Answer 12

Large cattle or mixed farms

Question 13

How long should immunity be following ring vaccination?

Answer 13

At least 6 months

Question 14

What is the problem with “vaccination to live”?

Answer 14

May miss long term carriers

Question 15

How can you diagnose in acute disease?

Answer 15

Virus isolation, antigen test, nucleic acid

Question 16

How can you diagnose in later disease?

Answer 16

Antibody test (serology)

Question 17

What is viraemia like in later disease?

Answer 17

Already reduced, but could be present in other animals

Question 18

How do you send skin scrapings?

Answer 18

Dry

Question 19

What do viral tubes contain?

Answer 19

Balanced salts, antibiotics, antimycotics

Question 20

What should you not do to viral samples?

Answer 20

Freeze

Question 21

How stable is serum?

Answer 21

Relatively

Question 22

How specific is PM for the virus?

Answer 22

Can only identify the type, not the specific virus

Question 23

What do you need for virus isolation and identification?

Answer 23

A replication competent virus and tissue to grow on

Question 24

What’s the problem with virus isolation and identification?

Answer 24

Get contamination, slow and expensive (2-3 weeks)

Question 25

Can you see oncogenic virus transformation in vitro?

Answer 25

Yes

Question 26

What happens to non-cytopathic BVDV in vitro?

Answer 26

Interferes with replication of indicator virus Newcastle disease virus

Question 27

What does Fowl plague cause in chicken eggs?

Answer 27

Death of embryo

Question 28

What does infectious bronchitis virus cause in chicken eggs?

Answer 28

Dwarfing of embryo

Question 29

What do fowlpox and herpesvirus (laryngotracheitis) cause in chicken eggs?

Answer 29

Pock lesions

Question 30

Which viruses was EM previously used for?

Answer 30

Orf and rotavirus

Question 31

What is the problem with EM?

Answer 31

Need very high titre

Question 32

What are the advantages of antigen or nucleic acid tests?

Answer 32

Easier, faster, detect non-viable virus, can't be contaminated easily, can be used after virus isolation

Question 33

What does precipitation on an Agar immunodiffusion test show?

Answer 33

Confirms antibody presence

Question 34

How do you test for a DNA virus?

Answer 34

PCR

Question 35

How do you test for an RNA virus?

Answer 35

Reverse transcriptase test first (RT)-PCR

Question 36

What is the advantage of real-time PCR?

Answer 36

Looks at what is produced after every cycle so is quicker and can be cleaner

Question 37

What does Next Generation Sequencing do?

Answer 37

Reads fragments of nucleic acids and compares to known sequences

Question 38

Why does a negative result not exclude the virus?

Answer 38

Could be neutralising Ab or bad method

Question 39

When might a positive result not indicative disease?

Answer 39

May be from subclinical shedding and something else is causing the disease

Question 40

How does a neutralisation test work?

Answer 40

Mix virus with test serum and if cells/eggs aren't infected them antibodies must be present

Question 41

How do you work out a titre?

Answer 41

Do assay with two-fold serial dilutions and the titre is the reciprocal of the dilution that gave the last positive result

Question 42

How do you identify a recent/active infection in an endemic area?

Answer 42

Take samples 2-4 weeks apart and titre will increase over 2 dilutions

Question 43

How do you diagnose an exotic disease?

Answer 43

Antibody positivity in just one sample

Question 44

When can you get a false positive for an endemic disease?

Answer 44

Cross reacts with endemic viruses giving low antibody titre

Question 45

What does antibody positive show in a PI animal?

Answer 45

Infected carrier

Question 46

What does antibody negative show in a PI animal?

Answer 46

Slow induction of Ab response so re-test in 6 months

Question 47

What should antibody status be after vaccination?

Answer 47

Positive

Question 48

How can you tell if infected or vaccinated?

Answer 48

DIVA ELISA

Question 49

How does DIVA work?

Answer 49

WT infection = gE present

Question 50

Why might some animals never become antibody positive?

Answer 50

Tolerant or immunosuppressed

Question 51

What kind of viruses may show antibody negative?

Answer 51

In-utero BVDV infection or FIV cats