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Farm Animal Final Year > BVD > Flashcards

BVD Flashcards

1
Q

Which virus causes BVD?

A

Pestivirus

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2
Q

What are the 2 biotpyes of related strains of BVD?

A
  • Non-cytopathogenic = BVDnc (persists in the cattle population)
  • Cytopathic = BVDc (arises from the non-cytopathic strain through spontaneous mutation)
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3
Q

What is type 1 and type 2 BVD?

A
  • Type 1 (most common presentations) – BVDnc and BVDc (the one we have in the UK and the most popular)
  • Type 2 (rare form in UK) - BVDnc and BVDc (more severe disease)
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4
Q

What is the clinical picture of type 1 BVDV?

Hint: Its a cute little flow diagram thing

A
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5
Q

ACute infection of type 1 BVD:

A) What are the clinical signs?

B) What is the viral clearance time?

C) What is the AB response?

A

A) Mild (diarrhoea, reduced production, often barely noticeable)

B) 10-14 days

C) Slow, plataeu at 10-12 weeks

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6
Q

When is BVD worse in calves?

A

Respiratory infection = +other viruses (IBR+RSV) +bacteria (M. haemolytica)

Enteric infection = BVDV +other viruses (corona & rota)

+bacteria (Salmonella spp. etc

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7
Q

Name 4 of the effects type 1 BVDV has on repro performance (5)

A
  • Embryo loss
  • Congenital defect
  • Abortion
  • Normal calf
  • PI calf
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8
Q

What is the effect if the cow is affected in the first third?

A

Foetus not immuno-competent

Embryonic death (early or late)

Foetal death and mummification

Foetus survives but born persistently infected (PI)

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9
Q

What is the effect if the cow is affected in the middle third? (3)

A

Foetus largely immuno competent

Foetal death/abortion

Foetus survives but born with congenital damage (due to the immune response to the virus)

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10
Q

What is the effect if the cow is affected in the last third? (3)

A

Foetus immuno -competent

Active foetal antibody response

Calf normal, virus negative

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11
Q

Name congenital defects of being affected with BVD in the middle third

A

cerebellar hypoplasia arthrogryposis, microphthalmia, cataracts, hydrocephalus, musculoskeletal malformations, and alopecia

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12
Q

What is the effect on the immune system of being a PI of BVDV?

A

No immune response to the virus

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13
Q

Is antibody/antigen positive or negative if there is a creation of a PI calf?

A

AB -ve

Ag +ve

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14
Q

Is antibody/antigen positive or negative if there is a creation of a normal calf, congenital defect or aborted calf?

A

AB +ve

Ag-ve

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15
Q

Is the AB and Ag positive or negative if there is a production of a normal calf when affected wth BVD in pregnancy?

A

Ab +ve Ag -ve

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16
Q

Where do PI come from? (2)

A

Cow who is PI will have a PI calf.. A lot of these don’t actually make it to give birth! So a vast majority of cases aren’t from here..

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17
Q

Which cows can the cyotpathic BVD affect?

A

Those with non-cytopathic infection of BVD (those with a poor immunity)

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18
Q

What are the clinical signs of mucosal disease?

A
  • Severe ulceration of the oral and gastrointestinal mucosa, often with foul smelling diarrhoea, weight loss and death
  • +/- respiratory signs
  • Often depressed, anorexic, dehydrated
  • Animals usually develop MD between 6-18 months
    • Range < 1 month to > 10 yrs
  • Usually rapid in onset and always fatal in outcome
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19
Q

What is the differential other than mucosal disease for this?

A

Differentials for this cow:

Foot and mouth (some of these CS wouldn’t be seen with F&M)

F&M – would probably see lameness too

Call the APHA if worried

20
Q

Which cows does mucosal disease develop in?

A

Those that are persistently infected with non cytopathic BVD virus

21
Q

Type 2 BVD:

A) What happens with the acute disease?
B) When is virus clearnace?

C) What are the signs?

D) What is the cross protection to Type 1 BVDV antibodies?

A

A) generally severe disease often fatal, usually adults

B) 28-38 days

C) thrombocytopenia, diarrhoea, haemorrhagic disease

D) Weak cross protection

22
Q

What are the 3 ways a bull can bring in BVD to a herd?

A
  • Can be PI
  • Can be acutely infected (be unlucky as usualy clear in 2-3 week)
  • Rare: virus can ‘hide’ in testicles “immunological privileged site”
    • Hence can be blood Ab positive, antigen negative yet still spreading virus!
    • Only identified by semen sample virus testing!!
    • Persistently produce PI sperm!
    • Cumulus effect
23
Q

How can you diagnose BVD?

A
  • Viral antigen and antibody tests
    • Both can be identified in blood and milk
      • Ag also skin, hair, semen etc
    • Both can be used on bulk milk (dairy herds)
      • Viral Ag can be detected in bulk milk, from 1 PI in 300 cows!
24
Q

How can we identify PI early in calves?

A
  • Virus can be readily identified in blood samples pre-colostrum or from older calves (>8mths)
    • detection in blood can be hampered in younger animals by maternal antibodies
  • Possible to look for viral Ag in calves of any age by using ear tissue samples, where high levels of antibody are less likely (part of the tagging process)
    • Special ear tags/applicators which collect tissue sample at same time as putting ear tag in
    • Tissue sample becomes sealed in the collector ‘cup’ which can be sent to a lab or tested on site.
    • Farmer can take sample
    • Feasible to do every calf born
    • Less likely to be masked by AB
25
Q

What are the 2 things the prescence of virus Ag) can mean?

A
  • Animal is a PI
  • Animal is acutely infected
26
Q

How do we demonstrate a PI animal?

A
  • 2 positive antigen tests >3 weeks apart (as you normally clear it in less than 3 weeks)
  • Usually PIs have low/no antibody levels in both samples
27
Q

Why is paried serology in an acute infection difficult?

A

A slow response

28
Q

What is the sensitivity and specificity of Ab and Ag test of BVD?

A

Very good

29
Q

Why do you need to be careful buying in pregnant cattle?

A
  • (the calf may be a PI)
  • The “Trojan horse” effect!
  • But have no angtien
  • So if you test pregnant before bringing in to a herd – no antigen. The calf will be infected.
30
Q

What are the main 2 questions to ask about BVD on a herd level?

A
  • Is BVD present in the herd
  • Are PI calves being produced?
31
Q

How does and ear tag biopsy anitgen testing work?

A
  • “Tag and test”
  • Newer way to tell whether PIs are being produced
  • More expensive (as test every animal)
  • But also shows which individuals are PIs
    • Allows culling
    • Normal also to test dam where PI revealed (although not always as could have been acutely infected)
  • Becoming a more common approach
    • Element of several eradication schemes
32
Q

How can you use blood sampling a hefier cohort to diagnose BVD?

A
  • From ~ 8 months of age (maternal Ab)
    • Usually sample 8-10 from group
    • Should be Ag and Ab negative
  • If Ab positive
    • must have seroconverted due to infection from a PI or
    • Contact with an adult (acute infection or PI)
  • Useful measure of whether infection is active in a herd
33
Q

How do we manage type 1 BVD?

A
  • Acute disease – no treatment (symptomatic if seen)
  • Mucosal disease – cull (incurable)
34
Q

How do we manage type 2 BVD?

A

•Symptomatic – grave prognosis (the acute infection is most of the time fatal)

35
Q

What is the basic apporach to BVD control?

A
  • Evaluate current herd status
  • Assess the routes by which virus could enter the herd and spread within the herd
36
Q

How can you go about managing the current status of the herd?

A
  • Initial screening commonly…
    • Bulk milk Ab +/- Ag test (dairy)
    • Youngstock cohort tests (dairy and beef herds)
  • Calf tag/test results useful
    • But normally only have these once farmer embarks on control programme
    • Definitive as to whether they are producing PI or not.
37
Q

What are the risks of viral entry into a herd?

A
  • Contact with cattle from another unit (e.g. across fences)
  • Contact through markets or shows
  • Shared, hired or new bull
  • BVDV status of bought-in cattle
38
Q

How is BVD transmitted?

A
  • Virus shed in nasopharyngeal secretions and urine. Faeces are a poor source of virus.
  • The main reservoir of infection is the persistently infected animal.
    • Virus has poor survival in the environment
  • Animals suffering from acute infection can also be a significant source.
  • (Sheep/deer can become infected although their significance in transmission is unclear) – probably very minor
39
Q

How can you prevent transmissio of BVD if present in the herd?

A
  • Vaccination – very effective
  • Removal of PIs – on the basis this is the infection source (so by getting rid of these you are eliminating)
  • Also maintain biosecurity to prevent (re)introduction of the virus
40
Q

What are the 4 options for a BVD positive herd?

A
  • “Do nothing” policy
  • Eradication – find all the PI and cull
  • Vaccination- protect all the others by vaccination and leave PI
  • Eradication and Vaccination – combo of the above
41
Q

What is the principles behind doing nothing in a BVD herd?

A
  • A proportion of the herd will acquire natural immunity
  • But this is random and immunity will wane over time
  • Losses that occur as a result of infection can be significant – but are very variable and can be hidden
42
Q

What are the principles behind eradication in a BVD herd?

A
  • Can quite reasonably do a PI hunt
  • Requires a very committed farmer and excellent biosecurity
  • Need to identify and remove any PI animals
    • Often via tag and test (i.e. from “now” onwards)
    • Time consuming and costly (lab fees)
    • Even when PI’s have gone, virus can still be present and slow spread via acute infection is theoretically possible
  • Continual monitoring of herd is required
  • Herd will become completely naïve, re-infection would result in large losses
  • Can just keep PI cows and then these will die out. Then by tag and test you can get rid of the PI calves
43
Q

What are the principles behind vaccinatig alone in a BVD herd?

A
  • AIM: Protect the breeding herd and stop the birth of PI animals
    • With time, any existing PI’s will be culled out naturally
    • Must ensure protection before first breeding
    • Bovilis BVD (Intervet), Bovidec (Novartis) and Bovela (Boehringer) currently available in UK
  • Care: PI animals sometimes still produced even after long period of vaccination
    • As PI cows will still have PI calves
  • Everything that is bred should be vaccinated – vaccinate BEFORE the first breeding. No marker vaccine (cannot distinguish)
44
Q

What are the principles behind vaccination and eradication in a BVD herd?

A

Find and remove PI animals then commence vaccination programme

Leads to the most rapid and complete resolution of BVD problems within the herd and protects against re-infection

(Several European countries have started BVDV eradication programmes based on this)

45
Q

What is the cattle health certification standards?

A
  • A self-regulatory body for cattle health schemes in the UK.
  • For the control and eradication of non-statutory diseases by a set of standards to which all licensed cattle health schemes must adhere.
  • Several schemes licensed
46
Q

What schemes are available in the UK to help eradicate BVD?

A
  • Voluntary national control schemes in England and Wales
  • Compulsory scheme in Scotland
  • Mandatory screening, restrictions on untested or “non-negative” herds
47
Q

Where do we put BVD on the differential list on a calf with scour?

A
  • Please remember BVD isn’t really a disease of primarily GI importance
  • The scour seen is usually mild and transient
  • It’s real importance is in fertility and immune compromise
  • Scour – can be on the differential – just not in top 5

Farm Animal Final Year (131 decks)

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