Infectious diseases: BVDV bovine viral diarrhea virus

Question 1

Outline BVDV transmission

Answer 1

Direct = nasal secretion*, semen, urine, milk, saliva, tears, foetal fluid i.e. nose to nose and sexual contact
Also indirect = ET, VETS, visitors

Question 2

What is the main source of virus

Answer 2

Persistently Infected

Question 3

What are 2 factors that affect what happens after infection

Answer 3

Immune status (defined by previous exposure and vaccination)
Pregnancy status

Question 4

Is BVD more serious if infecting a pregnant or non pregnant cow

Answer 4

More serious if pregnant

Question 5

When does BVD cause the most amount of damage

Answer 5

Not immune and pregnant cows affecting foetus

Question 6

When is the most critical period during pregancy when the calf could get persistently infected

Answer 6

First 4 months of preg

Question 7

What period of pregnancy will the calf be born with congenital defects if the dam gets infected

Answer 7

4-6 Months

Question 8

What period of pregnancy will the calf be seropositve and not persistently infected

Answer 8

7-9 Months

Question 9

What is the most common route of a cow being persistently infected

Answer 9

Foetus infected in first trimester
PI if mother if PI-7%. PI mother always produce PI calf

Question 10

PI cows still make antibodies (T/F)

Answer 10

False. Always antigen positive

Question 11

What is the cause of death for most PI calves

Answer 11

Mucosal disease. Virus mutates to be a cell killing virus. Mutated virus is transmissible

Question 12

C/S of mucosal disease

Answer 12

Ulceration of all mucosa
Oral ulceration
Salivation, Lameness, haemorrhagic diarrhoea

Question 13

How to advise farmers when they just imported a bull

Answer 13

Do not use bulls for at least 2 months

Question 14

Which is worse, transient BVD or Persistently Infected BVD

Answer 14

PI. Transient is like freshers flu

Question 15

How many genotypes does BVD have

Answer 15

Two type. BVD 1 more present in UK

Question 16

What makes BVD an effective virus

Answer 16

Non Cytopathic Virus-Multiplies in dividing cells without killing them
Crosses the placenta (PI and cong dz)
Causes inflammation of ovary and lowers LH (infertility)
Interrupts GI neurones (D+)

Question 17

What are two possible scenarios if a calf is PI

Answer 17

PI mother or Mother with TI

Question 18

Should I be looking at antigen or antibody levels if testing if an animal is PI

Answer 18

Antigen

Question 19

What happens if animal tested is Antigen positive

Answer 19

Retest in 3 weeks as it might be a transient infection

Question 20

If cow is antigen positive and antigen positive again after 3 weeks what is the likely scenario

Answer 20

PI

Question 21

If cow is antigen positive and antigen negative again after 3 weeks what is the likely scenario

Answer 21

TI

Question 22

What is the best sample to test for BVD

Answer 22

Blood or tissue
Tag test(tissue- from birth)
Blood 4-6 weeks

Question 23

Testing a calf for BVD is complicated due to maternally derived antibody. How long does it lasts in calf

Answer 23

9 months

Question 24

Why does MDA affect antibody testing

Answer 24

Can cause false positive. E.g. calf may appear exposed but was not

Question 25

Why does MDA affect antigen testing

Answer 25

MDA can neutralise antigens in PI. A PI animal can be missed.

Question 26

Why I cannot use blood samples if calf is less than 4-6 weeks

Answer 26

MDA

Question 27

How to test if herd is affected by BVD

Answer 27

Screen/check test- scottish gov scheme
5 calves 9-18 months in each management group
9 months = no MDA
Test blood for antibody i.e. exposure
Tells you if GROUP* exposed/immune to BVD
(not what calf is PI)
If positive need to hunt for the PI

Question 28

IMPORTANT: If there is a pos screen test, how Do i hunt for the PI

Answer 28

Test the WHOLE HERD for antigen. To save money, if calf is not PI, mother not a PI (saves money testing the mum)
Bulk milk antigen: can detect 1 Pi in 300 cows

Question 29

4 ways to control BVD

Answer 29

1. Biosecurity
2. Hunt and remove PI
3. Vaccination
4. Monitor

Question 30

What is the most common risks of having BVD in farm

Answer 30

Buying in animals; esp pregnant ones

Question 31

What happens if PI is found and removed

Answer 31

Concern about pregnant cows that may PI in uterus of cows not born yet. Continue testing FOR A YEAR

Question 32

What is important to ensure during vaccination protocols

Answer 32

Complete primary course before insemination/pregnancy
Not 100% effective in the face of massive challenge
Often incorrectly administered on-farm