BVD workshop Flashcards
What kind of virus causes BVD?
Pestivirus (single stranded positive RNA virus)
What is the effect of BVD on cattle?
Abortion
Mucosal disease
Immunosuppression
How does BVD spread within an animal?
- Virus replicates in the naso-pharyngeal mucosa.
- High titres develop in the tonsils.
- Virus spreads to regional lymph nodes.
- Leukocytes disseminate the virus systemically.
- Highest viral levels in tonsils, thymus, and ileum.
What are the two biotypes of BVD, and how do they differ?
Non-cytopathic (NCP): Doesn’t kill cells in culture, more common, can lead to persistent infection (PI)
Cytopathic (CP): Kills cells in culture, associated with mucosal disease in PI animals
What happens when a PI animal gets infected with the cytopathic BVD biotype?
Mucosal disease with acute diarrhoea, mouth ulcers, pyrexia & nasal discharge
How does non-cytopathic BVD affect bulls?
Infected semen can transmit BVD, leading to transient fever & mild diarrhoea
What are the clinical signs of non-cytopathic BVD in normal cattle?
Mild fever, transient leukopenia & possible diarrhoea
What are the effects of non-cytopathic BVD on youngstock?
Profound leukopenia & increased disease susceptibility
How does BVD infection affect pregnant females at different stages of gestation?
Early (<111 days): Abortion, congenital damage, PI calves
Mid (111-200 days): Congenital damage, fetal loss
Late (>200 days): No issues
How do persistently infected (PI) animals develop mucosal disease (MD)?
When they are super-infected with cytopathic BVD virus that has close antigenic relationship to resident non-cytopathic (ncp) BVDV, usually due to mutation or genome rearrangement of ncp-BVDV
How does mucosal disease develop and progress in PI animals?
It has rapid onset & initially affects tonsils, lymph nodes, Peyer’s patches & lower intestinal LN, eventually spreading diffusely in intestinal epithelium
Why do persistently infected (PI) animals not respond (no antibodies) to ncp-BVD?
Virus is present during fetal development, so it is recognised as “self,” leading to immunotolerance
They remain viraemic & constantly shed virus, never producing antibodies
What are the consequences of being persistently infected with BVD?
Decreased daily live weight gain (DLWG)
Increased risk of disease
What can you see in this PM examination?
Cerebellar hypoplasia
Give some examples of congenital defects in calves with BVD
Cerebellar hypoplasia
Microencephaly
Cataracts
Interstitial keratitis
Thymic hypoplasia
Hypotrichosis
Curly hair coat
Skeletal defects due to deranged osteogenesis
Growth retardation
Pulmonary hypoplasia
What are you going to do in a herd with calves tested positive for BVD?
Test for BVD
Have workers wear correct PPE
Vaccinate
Cull PI
What does antibody testing for BVD indicate?
It shows that there has been past infection or exposure to BVD
Why is the timing of antibody testing important in calves?
Maternal antibodies in milk can persist, but if there is no BVD exposure, they will wane by 8 months, making later testing more reliable for detecting true exposure
What does antigen testing for BVD detect?
It detects either circulating virus (acute infection) or persistently infected (PI) animal
What do these results in calves suggest?
All AB negative
Some antigen positive which shows presence of some PI animals or recent infection so no AB yet so look at previous tests
What are the key steps to eliminate BVD from a herd?
Assess Herd – Check biosecurity, vaccination & disease history
Define Herd Status – Test youngstock (antibody) or all calves (antigen/PCR)
Action Plan – If PIs are found, cull them & continue testing
Monitor Progress – Repeat testing regularly & test all bought-in animals
