Bovine viral diarrhoea Flashcards
Cause of BVD
- Bovine Viral Diarrhoea = pestivirus
- Single stranded positive sense RNA virus
Effects of BVD infection
- Abortion
- Mucosal disease
- Immunosuppression
What are the biotypes of BVD?
- Non-cytopathic
- Cytopathic (only in persistently infected animals)
What effect does BVD have if infection occurs early in gestation (<111 days)?
- Abortion
- Congenital damage
- Persistently infected calves who do not recognise the virus as foreign
What effect does BVD have if infection occurs in mid-gestation (111-200 days)?
- Congenital damage
- Foetal loss
What effect does BVD have if infection occurs in late gestation (>200 days)?
- No issues
What effect does BVD have on young stock?
- Profound leukopenia
- Increased disease susceptibility
What effect does BVD have on other cattle (non-cytopathic infection)?
- Mild fever
- ± transient leukopenia
- ± diarrhoea
What effect does BVD have on bulls (non-cytopathic infection)?
- Transient fever
- Slight diarrhoea
- Infected bulls transmit infection through their semen
What effect does a cytopathic BVD infection have on the animal?
Cytopathic infection = persistently infected animals only
- Mucosal disease:
- Acute diarrhoea with ulcers in the mouth
- Pyrexia
- Nasal discharge
- These animals may not always show mucosal disease; other times they may appear normal but just a bit runty.
When and how do persistently infected animals present with mucosal disease?
- Mucosal disease occurs when a PI animal is super-infected with a cytopathic virus which has a close antigenic relationship to the resident ncp-BVDV
- This is usually rapid onset
- Disease starts in the tonsils, lymph nodes, Peyer’s patches, and intestinal lymph nodes
- There is diffuse distribution in the intestinal epithelium
- Massive ulceration leads to death
Persistently infected animals don’t respond to ncp-BVD. Why?
- Timing of the infection as calf = immune tolerance
- These animals are viraemic: always shedding the virus
- They never produce antibodies to BVD
- The impact of being persistently infected = decreased DLWG, increased risk of disease
Persistently infected animals are ______ positive, _________ negative
Persistently infected animals are antigen positive, antibody negative
Relate this image to the clinical signs a calf infected with BVD would present with.
- Cerebellar hypoplasia
- Animal will shake and try to move but be unable
What are your differential diagnoses for congenital abnormalities/high empty scanning rates/abortion?
- Blue tongue virus → bigger effect on sheep
- Schmallenberg virus → leads to distinctive abnormalities (“spider calves”)
Questions to ask the farmer when BVD is a differential:
- Has it happened before?
- Have new bulls been brought onto the farm? Any new cows?
- How many sick calves?
- Any abortions and timing/high barren rate?
- Biosecurity on the farm?
- Visitors to the farm?
- Do they have sheep?
- Do they share borders with other farms?
If dairy cows, how could you test for BVD?
Test the bulk milk tank for BVD antigen
What are the benefits and drawbacks of doing antibody testing to detect BVD?
✅ Shows that there has been an infection
❌ Does not detect persistently infected animals
Don’t test calves. Cows are likely to test positive. Heifers, if positive, indicate recent exposure (perhaps BVD infection in the last year)
What are the benefits and drawbacks of using antigen-testing to detect BVD?
✅ Shows either circulating virus or persistently infected animals
- Perform the antibody test first.
- Test calves for the antigen to identify persistently infected animals.
What action should you take with a calf who tests positive on the antigen test?
- Isolate for a couple of weeks
- Retest
- If still positive = persistently infected. If negative = it was a transient infection
What action should you take if the herd is infected with BVD?
- Cull persistently infected calves
- Trace persistently infected dams but antigen-testing the mothers of cull calves
- Vaccinate cows prior to serving
- Put up double fencing on borders
- Introduce foot dips for visitors
- Don’t share kit/muck between farms
- Continue testing
True/false: freezing semen kills BVD.
False.
Need to test the semen.
If the bull was infected as a certain point in gestation, he could be serum -ve, semen +ve (check this)
