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mod 21 > BVD > Flashcards

BVD Flashcards

1
Q

how is BVD transmitted?

A 
direct via nasal secretion
semen
urine
milk
saliva
tears
foetal fluid
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2
Q

what is the main source of virus for BVD?

A

PI = persistently infected

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3
Q

what determines what happens after infection?

A

immune status

preg status

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4
Q

what does the antigen indicate?

A

virus (active infection)

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5
Q

what does the antibody indicate?

A

exposure/immunity to virus

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6
Q

what happens when cow infected but NOT pregnant?

A

if immune & not preg = nothing (or v mild TI)

if not immune & not preg = TI (transient)

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7
Q

what is TI?

A

rarely noticed
viraemia 3-14d only = antigen + (nasal shedding)
but immune response from d14 = recovery: Ab
Ag -ve but ab +ve

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8
Q

what happens when infected & pregnant? (if immune)

A

nothing
Ab clear virus
foetus unaffected

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9
Q

what happens when infected & preg (NOT immune)?

A

cow - TI & ab BUT bad news for foetus
if 1st trimester = PI, abort (0-120d)
if 2nd trimester = congenital defects, abort (120-240d)
if 3rd trimester = stillborn, stunted, abort (240-280d)

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10
Q

how do PIs come about?

A
  1. foetus infected in 1st trimester of preg:
    - before immunocompetent
    - BVDV seen as ‘self’
    - foetus/calf NEVER fights the virus (no Ab)
  2. offspring of PI
    - PI cow will alw produce PI calf (BVD gets into oocyst)

Ag +ve, ab -ve (if MDA used up) FOREVER!
massive source of virus on farm

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11
Q

CS of TI?

A 
often v little, all temp
? pyrexia
? D+ 
? anorexia
? infertility
? immunosuppression 
Ab peak @ 12wks after infection & remain for years (?lifelong)
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12
Q

is PI for life?

A

yes!!

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13
Q

impacts of PI?

A 
stunted, poor doing
poor DLWG
prone to 2dary infections: scour, pneumonia - can be underlying BVD prob 
90% under 2yo, most die
never make Ab
develop mucosa dx
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14
Q

how does mucosal dx occur in PIs?

A

mutation of own virus from NCP to CP/superinfection w w CP from another PI in pen
CP virus can circulate causing an outbreak of mucosal dx w/i PIs

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15
Q

CS of mucosal dx?

A 
ulceration of ALL mucosa
salivation
haemorrhagic D+ 
6mth-2y 
EUTH asap
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16
Q

ddx of oral ulceration?

A 
FMD
bluetongue
BVD/mucosal dx 
malignant catarrhal fever
calf diphtheria
actinobacillosis - wooden tongue
actinomycosis - lumpy jaw
trauma
(IBR)
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17
Q

which out of the ddx of oral ulceration is notifiable?

A

FMD

bluetongue

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18
Q

what are the effects of TI in bulls?

A

sperm motility & morphology affected temp
2 wks viraemia + 9wks spermatogenesis of new sperms
virus also sheds in semen (? up to 5mth i.e. longer than nasal secretions) - may be viable KIV

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19
Q

what are the effects of PI in bulls?

A

secrete virus in semen continually - sperm Q reduced

foetus may/may not be PI

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20
Q

what is a cumulus?

A

infection during puberty
Ag -ve, Ab +ve but Ag being produced in testes
v unusual

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21
Q

how long should farmers wait to use bulls after purchase?

A

2 months: can be TI despite -ve Ag test

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22
Q

how is the herd affected by BVD?

A 
if immune (+ not massive viral load) = v little
if herd not immune (naive & not vax) = abortion, still birth, congenital prob, D+, infertility, (immunosuppression), poor growth rates, decreased semen Q, mucosal dx cases, increase dx in gen.
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23
Q

what family is the BVDV from?

A

flaviviridae

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24
Q

what genus is BVDV?

A

pestivirus

25
Q

what genotypes of BVDV are there?

A 
2 genotypes
BVD1 = classic, UK 
BVD2 = more severe TI 
some vax only license for 1 genotype 
prone ot mutations = strain variation
26
Q

what biotypes of BVDV are there?

A

2 biotypes of each genotype
NCP = TI
CP = superinfect PIs to cause mucosal dx - kills cells; mutation of NCP

27
Q

which gene mutation results in NCP to CP?

A

NS2/3 mutation

28
Q

what makes BVDV an effective virus?

A 
multiplies in multiply cells w/o killing them (NCP) 
crossing placenta (PI & cong dx) 
causes inflammation of ovary & lowers LH (infertility) 
interrupts GI neurones (D+) 
causes immunosuppression
-hides from immune resp
-down regulates interferon
-decrease leucocyte no. (lymphopenia) 
-effects on B & T cell resp
29
Q

PI cow will ALWAYS give birth to PI calf: T/F?

A

true

30
Q

PI calf MIGHT have PI mother (or mother had TI when preg): T/F

A

true

31
Q

what are Ab results affected by?

A

MDA lasts 9mths (less in PI)

vax

32
Q

how to test if animal is PI?

A

test for antigen (blood, tissues, milk) - PCR/Ag ELISA
PI result = Ag +ve, BUT can be TI > retest in 3wks i.e. if TI, will clear virus & mount immune resp
3 wks later:
-result PI = Ag +ve (Ab +/-)
-result TI = Ag -ve (Ab +)

33
Q

how to test if animal has been exposed?

A 
test blood/milk for Ab
-ve = not exposed BUT is it PI?
-might want to test Ag to check 
\+ve = exposed/vax but...when?
calf - complicated bcs MDA
not done for single animal
34
Q

how long does MDA last for?

A

9 months

35
Q

how does MDA affect testing results?

A 
Ag testing:
-MDA can neutralise Ag in PI = false -ve
-PI missed
-don't use blood if <30d
-tissue ok from birth
Ab testing:
-false +ve if test calves <9mths
36
Q

what is the diagnostic gap?

A

MDA might give false -ve for tissue Ag
MDA effect in PI peaks @ 3wks
‘tag test early/test late’

37
Q

how to check if live calf exposed in utero?

A

1st check for Ag (foetal fluid/tissue) to see if PI
-if +ve & calf alive, retest in 3wks: if Ag +ve = PI, if Ag -ve = not PI but was it exposed in utero?
if not exposed in utero = Ab -ve
if exposed in utero (after 120d) = Ab +ve bcs immune system of foetus can produce Ab
BUT need pre-colostral sample to avoid MDA from colostrum
?practical
if Ab -ve (& Ag -ve) = calf not exposed in utero (rare to get this result due to vax/exp of mom)

38
Q

how to check if pregnant cow carrying PI in utero?

A

Ag (mom) +ve = could be PI mom, retest; if -ve = TI so maybe PI in utero
Ag -ve = not currently viraemic (could’ve previous TI)
Ab +ve = exposed/vax but dk when
Ab -ve = not exposed so in-utero infection unlikely (could also be PI)

39
Q

how to test if herd has been exposed to BVD?

A

screen test:
5 calves 9-18mths in each management group
test for Ab i.e. exp
tells you if GROUP exposed/immune to BVD
(not what calf is PI)
if +ve need to hunt for PI

40
Q

how does screen testing work?

A

PI secretes massive amt of virus
nose to nose contact allows spread
those in contact = TI, become Ab +ve in 3 wks
(if happened to sample PI it would be Ab -ve while the rest +ve)
£

41
Q

what is a management group?

A

nose to nose contact
tgt for 2+ months
not as effective @ grass

42
Q

if screen test results come back as all Ab -ve what does that mean?

A

no evidence of active BVD

monitor

43
Q

if screen test come back as occasional +ve, ‘not -ve’

A 
active BVD infection can't be ruled out
sample more from group
re-test if single +ve
check age
check if vax
hunt PI
44
Q

if screen test multiple +ves

A

active/recent BVD

hunt PI

45
Q

what are the problems w screen test?

A

relies on farmer’s honesty re. management groups
need accurate DOB for MDA
vax interferes
need distinct calf grps
if +ve - may have been PI on farm for 9mths already causing prbs
-defo other PI in utero (in mothers) that can’t be prevented

46
Q

what is the scottish gov BVD scheme for dairy cows?

A

screen test 10 calves q6mths bcs no distinct management groups

47
Q

how much of herd needs to be sero+ve for BT +ve?

A

5% herd

bulk milk Ab not that useful

48
Q

is bulk milk Ab useful?

A

not that useful (removed from scottish gov scheme)

lag btwn infection & +BMT (up to 36 mths)

49
Q

how to hunt for PI?

A

test whole herd for Ag - next step following +ve screen test
-tissue, blood, milk (indiv/bulk but NOT beef)
£££ but tells if there’s any PI
make sure you have test result for every animal (bulls, in calf heifers)
BUT what if PI has been sold/died?

50
Q

how to prevent sampling all cows for PI?

A

‘presumed -ve status’ but need to make sure a calf for every cow
can ‘pool’ blood samples (not <6wks old)
-if have +ve in batch, have to sample indiv
-pool all heathy animals tgt & any animals that sus, test separately
bulk milk can detect 1xPI in 300 cows

51
Q

how much does BVD Ab ELISA (blood) cost?

A

£4.10

52
Q

BVD Ab ELISA (milk) cost?

A

£5.35

53
Q

BVD Ag ELISA (blood) cost?
BVD PCR blood (Ag) cost?
BVD PCR BMT (Ag) cost?
BVD PCR tissue (Ag) cost?

A
  1. 80
  2. 45
  3. 45
  4. 70
54
Q

how long must we test for before considering stopping Ag testing?

A

have at least 12mth of no PIs born before can consider stopping Ag testing
make sure ALL animals tested for Ag

55
Q

risks for BVD?

A 
bought in animals* 
rented grazing away from farm*
heifer rearing away from farm*
showing/bringing home from market*
contact w neighbours stock (double fence!)
people: vet/staff/foot trimmers/AI tech
equipm
vehicles: milk tanker/feed deliveries

*esp impt if preg animals!

56
Q

control measures for open herds?

A 
test bought in animals for Ag
buy 'accredited free' animals
isolate 4 wks
avoid buying in calf animals (can't test unborn calf)
trojan cow! carrying PI: high Ab
57
Q

controls for BVD?

A

vax - complete 1ary course before insemination
not 100% effective when have massive challenge
often incorrectly admin on farm
vax Ab complicates testing

58
Q

what vax are there for BVD?

A

bovela (£4.95/dose)
modified live, BVD 1&2, single dose from 3mth, 3wks prior to service, not bulls
yearly booster

bovillis BVD (£2.47/dose)
inactivated BVD 1, 2 doses from 8 mth, 4wks prior to service
initial 6mth booster then 12mthly
can combine w IBR marker live

59
Q

what accreditation scheme is there?

A

CHeCS = regulatory body for cattle health scheme

mod 21 (12 decks)

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