Infectious diseases: BVDV bovine viral diarrhea virus Flashcards
Impt for CDM and PSQ
Outline BVDV transmission
Direct = nasal secretion*, semen, urine, milk, saliva, tears, foetal fluid i.e. nose to nose and sexual contact
Also indirect = ET, VETS, visitors
What is the main source of virus
Persistently Infected
What are 2 factors that affect what happens after infection
Immune status (defined by previous exposure and vaccination)
Pregnancy status
Is BVD more serious if infecting a pregnant or non pregnant cow
More serious if pregnant
When does BVD cause the most amount of damage
Not immune and pregnant cows affecting foetus
When is the most critical period during pregancy when the calf could get persistently infected
First 4 months of preg
What period of pregnancy will the calf be born with congenital defects if the dam gets infected
4-6 Months
What period of pregnancy will the calf be seropositve and not persistently infected
7-9 Months
What is the most common route of a cow being persistently infected
Foetus infected in first trimester
PI if mother if PI-7%. PI mother always produce PI calf
PI cows still make antibodies (T/F)
False. Always antigen positive
What is the cause of death for most PI calves
Mucosal disease. Virus mutates to be a cell killing virus. Mutated virus is transmissible
C/S of mucosal disease
Ulceration of all mucosa
Oral ulceration
Salivation, Lameness, haemorrhagic diarrhoea
How to advise farmers when they just imported a bull
Do not use bulls for at least 2 months
Which is worse, transient BVD or Persistently Infected BVD
PI. Transient is like freshers flu
How many genotypes does BVD have
Two type. BVD 1 more present in UK
What makes BVD an effective virus
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+)
What are two possible scenarios if a calf is PI
PI mother or Mother with TI
Should I be looking at antigen or antibody levels if testing if an animal is PI
Antigen
What happens if animal tested is Antigen positive
Retest in 3 weeks as it might be a transient infection
If cow is antigen positive and antigen positive again after 3 weeks what is the likely scenario
PI
If cow is antigen positive and antigen negative again after 3 weeks what is the likely scenario
TI
What is the best sample to test for BVD
Blood or tissue
Tag test(tissue- from birth)
Blood 4-6 weeks
Testing a calf for BVD is complicated due to maternally derived antibody. How long does it lasts in calf
9 months
Why does MDA affect antibody testing
Can cause false positive. E.g. calf may appear exposed but was not
Why does MDA affect antigen testing
MDA can neutralise antigens in PI. A PI animal can be missed.
Why I cannot use blood samples if calf is less than 4-6 weeks
MDA
How to test if herd is affected by BVD
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
IMPORTANT: If there is a pos screen test, how Do i hunt for the PI
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
4 ways to control BVD
- Biosecurity
- Hunt and remove PI
- Vaccination
- Monitor
What is the most common risks of having BVD in farm
Buying in animals; esp pregnant ones
What happens if PI is found and removed
Concern about pregnant cows that may PI in uterus of cows not born yet. Continue testing FOR A YEAR
What is important to ensure during vaccination protocols
Complete primary course before insemination/pregnancy
Not 100% effective in the face of massive challenge
Often incorrectly administered on-farm
