BVD Flashcards
Which virus causes BVD?
Pestivirus
What are the 2 biotpyes of related strains of BVD?
- Non-cytopathogenic = BVDnc (persists in the cattle population)
- Cytopathic = BVDc (arises from the non-cytopathic strain through spontaneous mutation)
What is type 1 and type 2 BVD?
- 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)
What is the clinical picture of type 1 BVDV?
Hint: Its a cute little flow diagram thing
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) Mild (diarrhoea, reduced production, often barely noticeable)
B) 10-14 days
C) Slow, plataeu at 10-12 weeks
When is BVD worse in calves?
Respiratory infection = +other viruses (IBR+RSV) +bacteria (M. haemolytica)
Enteric infection = BVDV +other viruses (corona & rota)
+bacteria (Salmonella spp. etc
Name 4 of the effects type 1 BVDV has on repro performance (5)
- Embryo loss
- Congenital defect
- Abortion
- Normal calf
- PI calf
What is the effect if the cow is affected in the first third?
Foetus not immuno-competent
Embryonic death (early or late)
Foetal death and mummification
Foetus survives but born persistently infected (PI)
What is the effect if the cow is affected in the middle third? (3)
Foetus largely immuno competent
Foetal death/abortion
Foetus survives but born with congenital damage (due to the immune response to the virus)
What is the effect if the cow is affected in the last third? (3)
Foetus immuno -competent
Active foetal antibody response
Calf normal, virus negative
Name congenital defects of being affected with BVD in the middle third
cerebellar hypoplasia arthrogryposis, microphthalmia, cataracts, hydrocephalus, musculoskeletal malformations, and alopecia
What is the effect on the immune system of being a PI of BVDV?
No immune response to the virus
Is antibody/antigen positive or negative if there is a creation of a PI calf?
AB -ve
Ag +ve
Is antibody/antigen positive or negative if there is a creation of a normal calf, congenital defect or aborted calf?
AB +ve
Ag-ve
Is the AB and Ag positive or negative if there is a production of a normal calf when affected wth BVD in pregnancy?
Ab +ve Ag -ve
Where do PI come from? (2)
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..
Which cows can the cyotpathic BVD affect?
Those with non-cytopathic infection of BVD (those with a poor immunity)
What are the clinical signs of mucosal disease?
- 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
What is the differential other than mucosal disease for this?
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
Which cows does mucosal disease develop in?
Those that are persistently infected with non cytopathic BVD virus
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) generally severe disease often fatal, usually adults
B) 28-38 days
C) thrombocytopenia, diarrhoea, haemorrhagic disease
D) Weak cross protection
What are the 3 ways a bull can bring in BVD to a herd?
- 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
How can you diagnose BVD?
- 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!
- Both can be identified in blood and milk
How can we identify PI early in calves?
- 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
What are the 2 things the prescence of virus Ag) can mean?
- Animal is a PI
- Animal is acutely infected
How do we demonstrate a PI animal?
- 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
Why is paried serology in an acute infection difficult?
A slow response
What is the sensitivity and specificity of Ab and Ag test of BVD?
Very good
Why do you need to be careful buying in pregnant cattle?
- (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.
What are the main 2 questions to ask about BVD on a herd level?
- Is BVD present in the herd
- Are PI calves being produced?
How does and ear tag biopsy anitgen testing work?
- “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
How can you use blood sampling a hefier cohort to diagnose BVD?
- 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
How do we manage type 1 BVD?
- Acute disease – no treatment (symptomatic if seen)
- Mucosal disease – cull (incurable)
How do we manage type 2 BVD?
•Symptomatic – grave prognosis (the acute infection is most of the time fatal)
What is the basic apporach to BVD control?
- Evaluate current herd status
- Assess the routes by which virus could enter the herd and spread within the herd
How can you go about managing the current status of the herd?
- 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.
What are the risks of viral entry into a herd?
- 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
How is BVD transmitted?
- 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
How can you prevent transmissio of BVD if present in the herd?
- 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
What are the 4 options for a BVD positive herd?
- “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
What is the principles behind doing nothing in a BVD herd?
- 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
What are the principles behind eradication in a BVD herd?
- 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
What are the principles behind vaccinatig alone in a BVD herd?
- 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)
What are the principles behind vaccination and eradication in a BVD herd?
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)
What is the cattle health certification standards?
- 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
What schemes are available in the UK to help eradicate BVD?
- Voluntary national control schemes in England and Wales
- Compulsory scheme in Scotland
- Mandatory screening, restrictions on untested or “non-negative” herds
Where do we put BVD on the differential list on a calf with scour?
- 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
