control of pestivirus infections in cattle · bovine pestivirus - bvdv first recognised in 1948 in...
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Control of Pestivirus Infections in Cattle P.D. Kirkland, Virology Laboratory, EMAI
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www.dpi.nsw.gov.au
Bovine Pestivirus - BVDV
First recognised in 1948 in USA
Bovine Viral Diarrhoea Virus (BVDV)
Mucosal Disease Virus
Classical Swine Fever
Border Disease
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www.dpi.nsw.gov.au
BVDV – What does it do?
Breeding and cattle
Reduced conception rates
Embryo and foetal deaths – reduced pregnancy rates
Abortions
Birth defects
Stillbirths, weak calves
Persistently infected (PI) progeny
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www.dpi.nsw.gov.au
Infection between days 90-180 of gestation
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www.dpi.nsw.gov.au
BVDV – What does it do?
Growing and mature cattle
Suppresses immune system
Increased chances of infection with other viruses and bacteria
Respiratory disease in intensively managed cattle – especially feedlots
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www.dpi.nsw.gov.au
BVDV – What does it do?
Persistently infected cattle
Outcome of infection at 30-90 days of gestation
Surviving calves small and usually grow poorly
Weaner ill-thrift
Deaths in weaners and yearlings
Indicate spread of virus in herd >9 mths ago
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www.dpi.nsw.gov.au
Persistently infected calves
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www.dpi.nsw.gov.au
Persistently Infected Animals
Carry virus for life
Shed large amounts of virus continuously
Few produce antibodies to the virus
Reservoir of virus in nature
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www.dpi.nsw.gov.au
How is the virus spread?
Virus is readily spread following close contact between a PI and a susceptible animal or contaminated environment
High rates of transmission with high stocking density/handling – can be 60% in 24 hours
Entry into a herd can be subtle – a pregnant female is exposed and foetus becomes a PI (cannot detect by testing dam) (including shows, sales)
No evidence of entry to herd until delivery of calf
Can be ‘over the fence’ as initial point source
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www.dpi.nsw.gov.au
How is the virus spread?
“Carrier” (PI) animals excrete virus in:
- aerosols
- discharges: nasal, ocular, uterine
- urine
- faeces
- milk
- semen
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www.dpi.nsw.gov.au
Incidence of persistently infected calves
Adult population - commonly 1%
New-born to yearling - extremely variable - can be very high (50%) in a problem herd
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www.dpi.nsw.gov.au
Incidence of BVDV infection
About 90% of herds have some immune animals
70% of herds have evidence of active or recent infection
Once the PI animal(s) die, quickly develop a susceptible herd
Can be fully susceptible mobs within an infected herd
Good management can create a problem (segregation)
Infection during agistment (eg drought)
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www.dpi.nsw.gov.au
What is the economic impact?
Some herds suffer no loss in the short term
Chronic low level losses (1-2% p.a.) may cost Qld herd up to $35M/year; indirect losses of $100M to state
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www.dpi.nsw.gov.au
What is the economic impact?
Herds with an outbreak
– many susceptible animals after PI deaths/culling
- Losses can be very high (up to 50% of calves)
Losses estimated at $100,000 in outbreak year
Takes up to 8 years to recover
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www.dpi.nsw.gov.au
Why control BVDV
Major problems often initiated by 1-2 PI animals
Can be inadvertent/disguised entry (eg pregnant cow)
that leads to high level losses
PI animals have reduced life expectancy, reduced productivity if they survive – not “fit for purpose” –
defective when sold & worthless
Potential liability for vendor
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www.dpi.nsw.gov.au
Control options
Control movement of PI animals?
Removal of PI animals (combined with other control measures)
Maximise mixing of breeders (>30days before joining)
Screen ET donors & bulls
Vaccination of breeders
Do nothing and expect a crash once every 8-10 years
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www.dpi.nsw.gov.au
Detection of PI animals
Accurate, quick inexpensive test (PACE)
Once in a lifetime
Range of sample types for live animals
- Blood or serum
- Skin samples – ‘ear notch’
- [Hair samples]
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www.dpi.nsw.gov.au
Recommendations
Adoption of BVDV control measures in stud and seed-stock producing herds (good test and vaccine)
Encourage testing of replacement breeding animals prior to sale
Testing of stud animals as a component of registration
Agricultural shows only include animals shown to be free of persistent infection with BVDV. [If stud animals tested for registration, further testing would not be required].
Testing of donors and recipient animals in embryo transfer programs where the progeny are likely to be sold.