11.3.3: BVD Flashcards
What is the causative agent of BVD? What types of BVD are there?
- BVD is caused by a pestivirus
- There is antigenic variation of the viral surface protein, producing 2 types.
- Majority of UK cases: Type 1
- Type 2 seen in Europe and US.
- Both forms can by cytopathic or non-cytopathic.
What are clinical signs of Type 1 BVD?
- Acute infection -> mild systemic illness, immunosuppression, reduced reproductive performance
- Persistently infected animals show mucosal disease
What the clinical signs of Type 2 BVDv?
True/false: transient infection with BVD can lead to immunosuppresion.
True
This is why have a PI calf, who is constantly shedding BVDv, can make other non PI calves more vulnerable to respiratory and enteric infections.
What is the effect of BVD infection in the non-pregnant animal?
What is the effect of BVD in the pregnant animal?
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2
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If a persistently infected animal has a calf, this calf will be:
a) normal
b) a PI animal
b) Persistently infected mothers produce persistently infected calves
True/false: if a persistently infected calf is identified, the calf’s mother must also be culled as she is a PI animal too.
False
She might be, but we need to check. She may just have been transiently infected during pregnancy and hence produced a PI calf.
Most PI calves come from transiently infected mothers, rather than PI dams.
Clinical signs of a persistently infected animal
They may be clinically normal!
What are the clinical signs of an animal with mucosal disease caused by BVD? How might you differentiate this from FMD?
What happens if a bull is transiently infected with BVD?
- The virus may induce temporary infertility
- During this time the virus may be detected in semen
- This is a transmission risk to cows
Describe how a bull could be antibody positive, antigen negative on bloods and yet be shedding BVD
Bull can be persistently infected but virus hides in testes (immune priviledged site). This is rare. (These are ‘Trojan horse’ bulls).
* Bull is infected in-utero (even after calf immune system has formed) and virus infected testis
* Therefore the bull will be born antibody positive and antigen negative on bloods
* BVD can be detected and spread in semen
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2
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What happens if a pregnant cow becomes infected with a cytopathic BVD?
True/false: once a PI animal has the cytopathic strain, they will then shed this strain and are at risk of kicking off other PIs.
True
How could you demonstrate an animal is a PI? What should you do with this animal?
- 2 positive antigen tests >3 weeks apart
- Usually PIs have no (or rarely low) antibodies in both samples
- PI animals represent a major reservoir of infection so should cull this animal
True/false: you can test for BVD antigen in the bulk milk tank.
True
This is detectable at a level of 1 PI in 300 cows.
If more than 300 cows may need to split them to sample.
How can we identify BVD antibody in an individual animal?
- Blood
- Milk
How can we test for BVD antigen in an individual animal?
- Blood
- Milk
- Semen
- Skin
- Hair
True/false: BVD is species-specific.
False
It can affect other species e.g. pigs and is close to Border Disease virus in sheep
BVD is
a) reportable
b) notifiable
c) neither
c) neither
When is a persistently infected animal created?
a) During pregnancy at any time
b) During first trimester
c) During second trimester
d) During third trimester
b) During first trimester
What method could you suggest to a farmer who is keen to identify and eradicate PI calves as soon as possible?
- Ear tag and test
- Special ear tag applicators take a sample at the same time as putting the tag in
- Put the sample in a sealed tissue pot and send to lab
- This is feasible to do immediately after the calf is born
True/false: some PI animals can make antibodies.
True but this is rare
True/false: paired serology to demonstrate rising titre is a good way to asses acute BVD infection in a herd.
False
Paired serology won’t necessarily show rising titre even in transient infection - response to BVD infection can be slow especially in cattle where it has caused abortion.
What is a useful way of monitoring if there is BVD actively circulating in a herd?
- Blood sample the heifer cohort from ~8 months old
- Sample 8-12 animals from the group
- These animals should be antibody (and antigen) negative if the herd considers itself free of BVD
- If these animals are antibody positive, they must have been exposed to a PI calf OR had contact with a transiently infected or PI adult
A calf has been aborted and you suspect BVD. Which sample will you send to the lab?
Send the calf spleen for PCR
True/false: there is a BVD vaccine but you should not use it because it interferes with testing of PIs.
False
There is a vaccine.
It does not affect your ability to test for PIs (because PIs will be consistently antigen positive)
It will lead to antibodies and these cannot be differentiated from those produced by a transient infection.
If you want to vaccinate cattle against BVD, when should you do it?
- Vaccinate prior to first breeding (maiden heifers around 10 months old)
- Continue to monitor BVD status of the herd
- Eventually PI animals should be culled and no more should be produced as long as the vaccination protocol is kept up
If you want to vaccinate cattle against BVD, when should you do it?
- Vaccinate prior to first breeding (maiden heifers around 10 months old)
- Continue to monitor BVD status of the herd
- Eventually PI animals should be culled and no more should be produced as long as the vaccination protocol is kept up
