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Module 21: Ruminant Production > Bovine Viral Diarrhea > Flashcards

Bovine Viral Diarrhea Flashcards

1
Q

how is BVD transmitted

A

Direct = nasal secretion, semen, urine, milk, saliva, tears, fetal fluid (not much in diarrhea)

  • Nose to nose
    • Sharing feed
  • Sexual contact

Indirect = ET, VETs, visitors

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2
Q

what is the main source of virus spread

A

persistently infected animals

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3
Q

what happens after infection depends on what

A
  1. immune status (defined by prev exposure or vaccine)
  2. pregnancy status
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4
Q

what occurs when infected and not pregnant if the animal is immune

A

Nothing

Or very mild transient infection

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5
Q

what occurs when infected and not pregnant if the animal is not immune

A

Transient infection (TI)

A bit like fresher’s flu

Rarely noticed

Viremia day 3-14 only = antigen + (nasal shedding)

But then, mount immune response from day 14, clear the virus and recover

  • = Antibody + (persists)
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6
Q

what happens when infected if immune and pregnant

A

Nothing

Antibodies clear the virus

Or

Very mild transient infection

Fetus unaffected

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7
Q

what happens when infected if not immune and pregnant

A

Cow — TI and antibodies but bad news for the fetus

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8
Q

what occurs to the fetus when dam is not immune and infected during 1st trimester

A

1st trimester: (0-120 days)

Persistently infected or abort

93% of PI’s produced this way

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9
Q

what occurs to the fetus when dam is not immune and infected during 2nd trimester (120-240 days)

A

Congenital defects

  • Cerebellar hypoplasia, ocular degeneration, undershot jaw, thymus/bone/growth retardation

Abort

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10
Q

what occurs to the fetus when dam is not immune and infected during 3rd trimester (240-280 days)

A

Still born

Stunted

Abort

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11
Q

how do persistent infections come about

A

Fetus infected in first trimester of pregnancy

Offspring of PI

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12
Q

how do PI’s occur in first trimester of pregnancy

A

Before immunocompetent

BVD virus seen as ‘self’

Fetus/calf NEVER fights the virus (no antibodies)

When the calf is produced it is a huge shedder! Never produce any antibodies

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13
Q

why does a PI cow always produce a PI offspring

A

A PI cow will ALWAYS produce a PI calf (BVD gets into oocyst)

Antigen positive, antibody negative (if MDA used up) forever!

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14
Q

what are the clinical signs of a transient infection (TI)

A

Often very little… all temporary

  • ? Pyrexia
  • ? Diarrhea
  • ? Anorexia
  • ? Infertility
  • ? Immunosuppression

Make antibodies = recovery and virus eliminated

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15
Q

how long after transient infection do antibodies peak

A

Antibodies peak 12 weeks after infected and remain for years (? lifelong)

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16
Q

are TI’s antigen +/- on day 1 and 21

are TI’s antibody +/- on day 1 and 21

A
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17
Q

what are the clinical signs of a persistent infection

A

Stunted, poor doing

Poor DLWG

Prone to secondary infections — scours, pneumonia, ringworm

90% under 2 years old, most of them die

Sometimes they look completely normal

  • Don’t presume if it’s a healthy animal that it can’t be a PI

Develop mucosal disease

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18
Q

are PI’s antigen +/- on day 1 and 21

are PI’s antibody +/- on day 1 and 21

A
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19
Q

what is mucosal disease due to BVD

A

Only happens in PI

Mutation of own virus from non-cytopathic (NCP) to cytopathic strain (CP) or superinfection with CP virus from another PI in pen

CP virus can circulate causing an outbreak of mucosal disease within PI’s

  • Kills cells AND the host

Ulceration of all mucosa, salivation, lameness, hemorrhagic diarrhea (probably where BV’D’)

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20
Q

how do you treat mucosal disease due to BVD

A

6 months to 2 years

Euthanize asap

No treatment

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21
Q

what are ddx for oral ulcerations

A

Foot and mouth disease (notifiable)

Bluetongue (notifiable)

Bovine viral diarrhea (BVD)/mucosal disease

Malignant catarrhal fever

Bovine papular stomatitis (BPS)

Calf diphtheria

Actinobacillus — wooden tongue

Actinomycosis — lumpy jaw

Trauma

(IBR)

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22
Q

what occurs to TI bulls

A

Sperm motility and morphology affected temporarily (2 weeks viremia + 9 weeks spermatogenesis)

Virus also shed in semen (Up to 5 months ie longer than nasal secretions)

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23
Q

what occurs to PI bulls

A

Secrete virus in semen continually

Sperm quality reduced, fetus may/may not be PI (compared to mother)

No reports of this phenomenon causing an outbreak

Advise farmers not to use bulls for 2 months after purchase

  • Even it has a negative antigen test
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24
Q

what are the clinical manifestations in the herd if the herd is immune

A

If herd immune (+ not massive viral load):

Very little

25
Q

what are the clinical manifestations in the herd if the herd is not immune

A

Abortion, still birth, congenital problems, diarrhea, infertility (immunosuppression), poor growth rates, decreased semen quality, mucosal disease cases, increase disease in general

26
Q

what type of virus causes BVD

A

Flaviviridae (family)

Pestivirus (genus)

Species:

  • Bovine viral diarrhea
  • Border disease virus (BDV in sheep)
  • Classical swine fever virus (CSFV)
27
Q

what are the 2 genotypes of BVD

A

BVD 1 - classic, UK

BVD 2 - more severe TI

subgenotypes and variation

28
Q

what are the 2 biotypes of BVD

A

noncytopathic (NCP)

cytopathic (CP)

29
Q

what are the differences between the noncytopathic and cytopathic genotypes

A

NCP causes the TI’s

CP superinfects PI’s to cause mucosal disease and kills cells –> mutation of NCP

30
Q

is the BVD virus prone to mutation

A

yes so strain variation

vaccines not 100%, variable virulence

31
Q

what makes the BVD an effective virus

A

Multiples in dividing cells without killing them (NCP)

Crosses the placenta (PI and congenital diseases)

Causes inflammation of ovary and lowers LH (infertility)

Interrupts GI neurones (diarrhea)

Causes immunosuppression:

  • Hides from the immune response
  • Down regulates interferon
  • Decreases leukocyte number (lymphopenia)
  • Effect on B and T cell response
32
Q

what are key points to remember about BVD testing (4)

A

You can not ‘become’ PI —> only born a PI

PI cow will ALWAYS give birth to a PI calf

PI calf MIGHT have a PI mother (or mother had TI when pregnant)

If calf not a PI, mother definitely not PI — presumed negative status

33
Q

what might antibody results be affected by

A

MDA lasts 9 months (less in PI)

Vaccination

34
Q

how do you test an individual animal to determine if they are a PI

A

test for antigen

PI result = antigen positive

  • But it could be TI
  • Re-test in 3 weeks
  • If TI animal will clear virus and mount immune response

3 weeks later:

  • PI result = antigen + (antibody +/-)
  • TI result = antigen - (antibody +)
35
Q

how do you determine if an animal has been exposed

A

Not often done for a single animal

  • Ex. buying in calf cows

Test blood (or milk) for antibody

  • Negative = not exposed… or is this a PI?
  • Positive = exposed or vaccinated but… when?

Calf is complicated due to maternally derived antibody

36
Q

how do you test calves for antibodies and interpret resuts

A

Acquired from mother’s colostrum, lasts 9 months

Antibody testing:

  • Can give false positive result if test calves <9 months
  • In other words, the animal appears to have been exposed but wasn’t
37
Q

how do you test calves for antigens and interpret resuts

A

MDA can neutralize antigen in PI — false negative

In other words, a PI animal is missed

But antibody used up really quickly in PI as so much virus

So blood NOT used for antigen <30 days

Tissue okay from birth (MDA doesn’t get into ear so well)

38
Q

where is the diagnostic gap in testing calves

A

Where MDA might give false negative for tissue antigen

MDA effect in PI peaks at 3 weeks

Tag test early or test late

39
Q

how do you determine if a calf was exposed in utero

A

First check antigen test (fetal fluid or tissue) to see if PI:

If positive (and calf alive), re-test in 3 weeks

  • If antigen positive = PI calf
  • If antigen negative = calf is not a PI but… was it exposed in utero?

If not exposed in utero = antibody negative

If was exposed in utero (after 120 days) = antibody positive because immune system of fetus can produce antibodies at stage of pregnancy

But as soon as calf suckles it acquires MDA from colostrum and becomes antibody positive (ie false positive) so need pre-colostral sample? Not practical

If antibody negative (and antigen negative) = calf was not exposed in utero (rare to get this result due to vaccine/exposure of mother)

40
Q

how do you determine if a cow is carrying a PI calf in utero (aka trojan cow)

A

No easy way to work this out

Can’t test the unborn fetus

Can test pregnant mother for antigen and antibody but…

Don’t buy in pregnant animals (testing confusing)

41
Q

how do you determine if a herd has been exposed to BVD using a screen test

A

5 calves 9-18 months in each management group

  • Test blood for antibody ex. exposure
  • Tells you if group exposed/immune to BVD (not what calf is PI)

If positive need to hunt for the PI

42
Q

how does a screen test work

A

PI secretes massive amounts of virus

Nose to nose contact allows spread of virus

Those in contact = TI and become antibody positive

If you happened to sample the PI it would be antibody negative and the rest would be antibody positive

43
Q

when doing a screen test, what is a management group

A

nose to nose contact

together for 2 months+

not as effective as grass

44
Q

does this herd have BVD

A
45
Q

what are the issues with a screen test

A

Relies on farmers honesty re management problems

Need accurate DOB for MDA

Vaccination interference

Need distinct calf groups

If positive — maybe have a PI on farm for 9 months already causing problems

Can test more calves

Can test more often

Scottish Govt BVD scheme — dairy, screen test 10 calves every 6 months as not distinct management groups

46
Q

how do you use a milk body antibody test to determine if a herd has been exposed to BVD and what are the issues with this test

A

Not that useful

5% herd need to be seropositive before BT positive

Lag between infection and + BMT (up to 36 months)

If positive = exposure or vaccination (no idea when, how many, if any PI’s)

Next step is hunt for PI

If negative = no BVD (rare as most vaccinated)

Removed from Scottish Govt scheme

47
Q

how do you hunt for the PI

A

Test the whole herd for antigen

Next step following positive screen test

Tissue, blood, milk sample (individual or bulk but NOT

£££ but tells you if any PI’s

Make sure you have test result for every animal (bulls, in calf heifers)

But what if the PI has been sold or died

48
Q

how can you hunt for the PI and be strategic/cost saving

A

Handy tricks:

  • Presumed negative status (saves sampling all cows) but need to make sure a calf for every cow
  • If cow is a PI her calf will be a PI
  • Can pool blood samples (not <6 weeks)
  • Bulk milk can detect 1 x PI in 300 cows
49
Q

what are the possible test outcomes and what do you always need to consider when interpreting results

A

always think about

age

mda

vaxx status

50
Q

what does BVD cost the farmer

A

estimated £37 per annum per cow in beef herd

£200 per cow over a few months in an outbreak in a dairy herd

PI calves 43-73kg less at weaning

51
Q

what are the areas of control of BVD

A
52
Q

how is BVD controlled

A
  1. biosecurity
  2. hunt and remove PI’s
  3. vaccination
  4. monitor
53
Q

how does hunting and removing the PI’s help control BVD in a herd

A

Fundamental to any control programme

Make sure ALL animals tested for antigen

Need to have at least 12 months of no PI’s born before can consider stopping antigen testing

  • Calves in-utero

Farmers keen to keep/attempt to fatten PI’s

  • It doesn’t work!
54
Q

what biosecurity points are key to controlling BVD

A

Reason for most breakdowns

What are the common risks?

  • Bought in animals — maintain a closed herd (if possible)*
  • Rented grazing away from farm*
  • Heifer rearing away from farm*
  • Showing/bringing home from market (if do treat as bought in animal)*
  • Contact with neighbours stock (double fencing)

People:

  • Vets, staff, foot trimmers, AI technician

Equipment

  • Vehicles
  • Knacker lorry, milk tanker, feed deliveries

***especially if pregnant animals

55
Q

if a farmer has an open farm what are key biosecurity points

A

If open herd:

  • Test bought in animals for antigen
  • Buy ‘accredited free’ animals
  • Isolate 4 weeks
  • Avoid buying in calf animals (can’t test unborn calf)
  • Trojan cow — carrying PI high antibody
56
Q

how can vaccination be used to control BVD

A

complete primary course before insemination

not 100% effective in the face of massive challenge

57
Q

what are caviets to vaccine and controlling BVD

A

often incorrectly administered on farm

vaccine antibody complicates testing

prev vaccine used as primary control without removing PI’s

58
Q

what are the key elements of Scottish Gov BVD scheme

A

all breeding herd must test

  • establishes ‘negative’ or ‘not negative’

if herd not negative:

  • Further testing to ID the issues (compulsory if >15 months not negative)
  • Can’t move animals off farm without an individual antigen test
  • Can’t move animals onto farm
  • Status of herd communicated online ‘name and shame’

illegal to move PI’s except to slaughter (can get special licence)

vets have authority to change status

if negative herd brings in animal of unknown or not negative status they will lose negative status

59
Q

what is the CHeCS accredidation scheme

A

regulatory body for cattle health scheme

various reasons to join (pedigree sotck, eradication of disease)

Module 21: Ruminant Production (21 decks)

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