Bovine Viral Diarrhoea

Question 1

Why is BVD important?

Answer 1

Economic impact
- poor reproductive performances
- growth retardation
- reduced milk yield
- increased susceptibility to other diseases
- early culling increased mortality among youngstock

Question 2

Which BVDV type is most prevalent in the UK?

Answer 2

Type 1

Question 3

How is BVD transmitted?

Answer 3

Nose-to-nose contact is the main route for the transmission of infection
* Most commonly by introducing infected animal(s) to herd (ie.shows etc)
* Virus survives poorly in the environment and fomites
* PIs are generally much more important sources of infection
* Most transmission is via nasopharyngeal secretions (faeces are a poor source)

Question 4

What are the clinical signs of BVD in non pregnant animals? During breeding? During pregnancy? In mucosal disease? In bulls?

Answer 4

• Non-pregnant adult animals
  
  • transient infection
  • Subclinical or clinical (dull, decreased appetite, D+)
  • Shed low levels for up to 3 weeks
  • Antibodies present from 2-4 weeks pi and persist for several years
• in youngstock, they are more prone to respiratory and enteric infections
• During breeding
  
  • lowered herd fertility
  • increased number of barren cows
  • decreased number of newborn calves
• During pregnancy
  
  • embryo loss (day 0-30)
  • congenital defects (day 90-210)
  • abortion (day 90-210)
  • normal calf (day 90 to end of pregnancy)
  • PI calf (day 30-120): more likely to come from acute infection of the dam than from a PI cow
• Mucosal disease - transmitting while alive
  
  • weight loss
  • bloody D+
  • dehydration
  • ulcerated lesions in mouth, nose and interdigital space
  • fatal condition
• Bull
  
  • can be PI or acutely infected
  • transient fever
  • slight diarrhoea

Question 5

What is the difference in clinical signs between BVD 1 and BVD 2?

Answer 5

BVD1
* Acute infection
* Mild systemic illness
* Reduced reproductive performance
* Immunosuppression
* Mucosal disease (PI animals)

BVD2
* Acute severe haemorrhagic syndrome
* Has been seen in UK but not very recently/widely

Question 6

How can we diagnose BVD in adults and PI calves?

Answer 6

• Viral antigen and antibody test
  
  • both can be identified in blood and milk (& semen)
• Early identification of PI calves
  
  • Blood antigen
  • tag and test

Question 7

What is a good diagnosis protocol?

Answer 7

• Bulk milk Ab ELISA test (dairy)
• Bulk milk Ag PCR test (dairy)
• Youngstock cohort tests (dairy and beef herds)
• What about calf tag/test results?
  
  • Normally when a farmer embarks on a control programme
• PM results?
• Abortion results?

Question 8

What does a positive antigen test mean? What test results do we need to demonstrate a PI animal? What should we do with a PI animal?

Answer 8

• Positive Ag - presence of virus
  
  • animal is PI
  • animal is acutely infected (viraemia post-infection lasts up to 2 weeks)

PI demonstration
- 2 positive antigen tests >3 weeks apart
- Usually, PIs have low/no antibody levels in both samples

• Cull PI animals as they represent major reservoir of infection

Question 9

What antibody levels are acceptable in the bulk tank milk?

Answer 9

Question 10

What diagnosis protocol should you follow in a cohort of heifers?

Answer 10

• Blood sample for Ab from ~ 8 months of age (maternal Ab)
• Usually sample 8-10 from group
• Should be Ab negative (and Ag if it was tested)

What does it mean if a heifer is Ab positive?
* Must have seroconverted due to infection from a PI
* Contact with an adult (acute infection or PI)

Why do we use it?
* Useful measure of whether infection is active in a herd

Question 11

How can we prevent BVD?

Answer 11

• Requires a committed farmer and excellent biosecurity
• Need to identify and remove any PI animals (tag test & PI bulk tank)
• Herd will become completely naïve; re-infection could result in large losses
• Commonly stop Ag testing calves at some point (often 1 year after the last positive) and rely on bulk milk antibodies to detect the incursion
• vaccination protocol

Question 12

What are the aims of the eradication programme?

Answer 12

• Protect the breeding herd and stop the birth of PI animals
  
  • With time, any existing PIs will be culled out naturally
  • Must ensure protection before first breeding
• PI animals are sometimes still produced even after a long period of vaccination
  
  • As PI cows will still have PI calves
  • Can be important for calf health