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Module 21: Ruminant Production > IBR > Flashcards

IBR Flashcards

1
Q

what are the issues with endemic diseases

A

herd often already endemically infected

maintained by shedding carriers/subclinically infected animals

signs often non-specific

challenge to diagnose and control

diagnosing disease - in carriers/asymptomatic

control - what does vaccination do in an animal already infected?

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2
Q

what is the virus that causes IBR

A

bovine herpes virus 1

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3
Q

what diseases does BoHV-1 cause

A

Infectious bovine rhinotracheitis (IBR)

Infectious pustular vulvovaginitis (IPV)

Infectious pustular balanoposthitis (IPB)

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4
Q

what is IBR

A

the most common clinical manifestion of disease that occurs during primary infection with BoHV-1

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5
Q

what are the 8 herpes viruses

A
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6
Q

what are the 3 recognized sub-types of BoHV-1

A

BoHV-1.1 mainly causes IBR and can cause abortion

BoHV-1.2a mainly causes IPV/IPB and can cause abortion (venereal manifestations)

BoHV-1.2b mainly causes IPV/IPB but doesn’t cause abortion (venereal w/o abortion)

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7
Q

what are the virus features of BoHV-1

A

Within lipid envelope there are different glycoproteins which stimulate production of antibodies

  • Glycoprotein E and B stimulate antibodies specific to these antigens
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8
Q

what are the manifestations of BoHV-1 in the individual animal

A
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9
Q

how is BoHV-1 spread

A

mainly by direct contact

resp secretions

  • nose to nose contact and asersol within 3-5m

repro secretions

  • semen and female reproductive fluid

indirect spread

  • fluid on outer clothing
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10
Q

what are the clinical signs of a primary infection

A

only stage commonly associated with clinical signs:

  • Dullness and reduced appetite
  • Pyrexia
  • Sudden reduction in milk production
  • Conjunctivitis
  • Nasal and ocular discharge
  • Pharyngitis/tracheitis
  • Rapid and loud breathing sometimes with a cough
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11
Q

what are other clinical syndromes of primary infections

A

abortion

embryo death (documented in maiden heifers)

neurological meningitis in neonatal calves

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12
Q

what is BoHV-1 apart of

A

bovine respiratory disease complex (BRDC)

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13
Q

what is the antibody response in a primary infection

A

fast and sustained

usually measure antibodies to 2 different surface glycoproteins (B & E)

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14
Q

what is the latent infection of BoHV-1

A

Virus becomes latent in nerve ganglion and antibody titre persists

  • Usually dorsal root ganglion of the trigeminal nerve with respiratory infection

No viral replication

Virus does not cause cell death

Has the potential to reactivate for life of animal

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15
Q

what can reactivate a latent infection

A

Calving

Transport

High dose dexamethasone treatment

Lameness, disease, nutritional stress

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16
Q

is the virus shed during the latent reactivation period

A

Virus is shed (less than during primary infection)

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17
Q

are there clinical signs once the latent virus has been reactivated

A

Clinical signs are absent or very mild

Antibodies are re-stimulated

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18
Q

why is the latent infection important to control

A

The latency/reactivation cycle has a deep epidemiological impact since it is responsible for the maintenance of BoHV-1 in a cattle herd

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19
Q

what is a sero-negative latent carrier

A

infection during the period of MDA cover can lead to latent infection without circulating antibody

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20
Q

how is BoHV-1 diagnosed in an acutely sick animal

A

direct test:

  • Ocular conjunctival swab
  • Guarded nasopharyngeal swab
  • PCR
  • Virus isolation
  • Fluorescent (FAT)
21
Q

how can BoHV-1 be diagnosed using serological antibody testing

A

Can test for antibodies for gE or gB

Generally not that useful for diagnosis of acute infection

ESSENTIAL for diagnosis and control at herd level

Paired serology very early after exposure may be only exception, but better to use a swab

22
Q

how is an acutely infected animal treated

A

NSAIDs

Antibiotics if you consider the animal at risk for secondary infection

Consider vaccination in the face of infection if you have confirmed the diagnosis

23
Q

what are BoHV-1 vaccines licensed to do

A

Reduce the severity of clinical signs in primary infection

Reduce shedding during primary infection

Reduce the likelihood and duration of shedding from reactivation

24
Q

what do BoHV-1 vaccines not prevent

A

Vaccines do not prevent latent infection or re-activation

25
Q

what BoHV-1 vaccines are available

A

Live — marker/conventional

Dead — marker/conventional

Marker - glycoprotein E +/- tK missing from the surface

26
Q

which are better during an outbreak live or dead vaccines

A

Live vaccines offer both better protection against clinical signs and a reduction of viral shedding in newly infected animals than inactivated vaccines

During an outbreak, live vaccines offer faster protection against clinical signs when used intranasally (interferon response)

27
Q

what is the serological response following a vaccination

A

Conventional vaccine get an antibody response to both gE and gB

Marker vaccine only gives you a response from gB

28
Q

how do you interpret serology results

A

you must chose which test you run at the lab

antibodies against gB or gE

29
Q

how do initial outbreaks of IBR occur

A

New introduction into naive herd

  • May not see any signs

Many animals suffering primary infection together

May see severe clinical disease in many animals

Tends to spread from pen to pen

30
Q

why are there no clinical signs of an initial outbreak of IBR

A

Virulence and challenge of the virus vs the resilience and resistance of the animals

Varies on the virulence of the strain

31
Q

how does an endemic infection occur

A
32
Q

what is herd (or national) prevalence defined as

A

of infected herds/# of herds in the country

approx 70% for dairy and 30 for beef

33
Q

what is prevalence within a herd defined as

A

of infected cows/# of cows in the herd

hugely variable

these individual animals are latent carriers

34
Q

what is the approach to herd control

A
  1. a clear goal
  2. coordination of essential components
  3. monitoring of progress
35
Q

what are the goals of IBR control

A
  1. remain free from BoHV-1
  2. eliminate BoHV-1 from the herd as fast as possible
  3. to prevent the spread of BoHV-1 to disease free stock entering the herd in order to reduce within herd prevalence over time
  4. or to live with the disease and minimize impact
36
Q

what are the options to herd testing

A

A proportion of animals in the herd OR all the animals in the herd

And

Combine the samples and run one test OR test the individual samples and combine the results

37
Q

what are the problems with direct tests

A

Remember the direct tests are limited as infected animals will only shed for short periods of time (7-10d) with the primary infection

38
Q

what are the issues with using direct tests from milk

A

poor sensitivity if less than 20% animals infected

Indicate latent infection BUT must be interpreted with vaccine status

39
Q

how could you determine if the herd is infected (are there any latently infected animals?)

A

Historical lab results:

  • Cheapest available method, specificity excellent, sensitivity likely to be very poor

Bulk milk tank antibody test:

  • Next cheapest for dairy herds
  • Poor sensitivity when less than 20% of the herd infected

Test a proportion of the individual animals by antibody test:

  • Most expensive and reliable
  • “Snapshot” — 30 animals >9 months (RANDOM)
    • 0 or 1 positive — 0-15% prevalence
    • More than 1 positive — >15% prevalence
40
Q

how do you tell how many animals are likely to be latently infected

A

Test a proportion of the individual animals by antibody test

  • Only reasonable option
  • Gets more reliable with increased numbers of animals tested
41
Q

how do you tell which animals are latently infected

A

Must test all animals in the herd

  • Most expensive option
  • Probably only appropriate in the final stages of a herd eradication program
42
Q

what are the 3 herd statuses

A

1. not infected

to remain free from BoHV-1

2. infected, low prevalence of latently infected animals

to eliminate BoHV-1 from the herd as fast as possible

3. infected, moderate or high prevalence of infected animals

to prevent spread of BoHV-1 to incoming stock in order to reduce prevalence over time

43
Q

what are the 3 elements of IBR control

A
  1. bio-exclusion
  2. cull/isolate latently infected animals
  3. regular, complete herd vaccination to reduce source and spread
44
Q

how do you cull/isolate latently infected animals

A

Air-space isolation can prevent spread

Increasingly impractical when more animals are latently infected

Will not be appropriate for most herds

Should only be used in low prevalence herds aiming for disease freedom

45
Q

how should regular herd vaccination be done to control IBR

A

Complete and regular herd vaccination reduces likelihood of ongoing spread

  • Suppresses shedding following re-activation

If we can reduce spread for several years prevalence will reduce as infected animals are replaced with non-infected

You can only monitor the success of marker vaccination

46
Q

how do you monitor progress of control of IBR

A

Repeat investigation herd testing at regular intervals

Refer back to your original goals

47
Q

how is BoHV-1 controlled at AI stations

A

Shed in semen

Animals entering AI stations where semen is used for trade within the EU must not be gE or gB antibody positive

They must not be infected or vaccinated against IBR

Remember live vaccines can spread on farm

48
Q

what are the national control programs in the UK

A

no coordinated program for control in UK

Module 21: Ruminant Production (21 decks)

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