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Module 21: Ruminant Production > Johne's > Flashcards

Johne's Flashcards

1
Q

what is the agent that causes johne’s infection

A

mycobacterium avium subspecies paratuberculosis (MAP)

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2
Q

how long does MAP survive in the environment

A

>1 year on pasture

slurry and water

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3
Q

what species can MAP infect

A

sheep

deer

rabbits

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4
Q

what is the transmission of johne’s

A

feco-oral

transplacental

via milk or colostrum

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5
Q

when do most johne’s infections occur

A

80% occur in the first month of life

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6
Q

how do infected animals shed MAP

A

feces (udder, environment, slurry, water sources)

milk

unborn calf

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7
Q

which animals are most susceptible in a herd to johne’s

A

calves

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8
Q

what is the economic impact of johne’s

A

Difficult to estimate as:

  • Subclinical
  • Infected animals often culled for other reasons
    • Lameness
    • Infertility
    • Reduced milk
  • Can be high if valuable bull
  • Becomes apparent at 3-5 years so may impact greater in beef breeding animals due to reduced productive lifespan
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9
Q

what is the pathophysiology of johne’s disease

A

MAP localizes in GIT:

  • Cell-mediated immune response may, or may not, eliminate MAP
  • Chronic granulomatous enteritis
    • Thickening of intestinal wall, especially terminal ileum

Protein-losing enteropathy (PLE)

  • Decreased albumin
  • Progressive weight loss
  • Diarrhea
  • Edema
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10
Q

what are the clinical signs of johne’s in dairy cows

A

Reduced milk yield

Increased ICSCC

Reduced fertility

Poor body condition

Usually culled for poor performance

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11
Q

what are the clnical signs of johnes in beef

A

Poor fertility

Small calf born, ill-thrift, poor performing

Poor condition

Diarrhea

Peripheral edema

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12
Q

describe the course of infection of johnes

A

Can take up to 2-3yrs post infection to become infectious

Many animals thought to clear infection with cellular response (yellow) they don’t become infectious

Takes awhile for animal to develop antibodies until 18months and antibodies rise over time and can’t be detected at low levels — around 3yrs when can be detected in blood

Antibodies increase as years go by and the disease progresses

Initially there is no shedding in feces, a couple years, around 3 years until there is shedding

5-6 years with full blown Johne’s, likely affected as a young calf —> tip of the iceberg

Animals may be removed from herd until they reach the end stage —> so may not even see the full blown disease

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13
Q

how long does it take for an animal to become infectious

A

Can take up to 2-3yrs post infection to become infectious

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14
Q

how do animals clear infections and do they become infectious

A

Many animals thought to clear infection with cellular response (yellow) they don’t become infectious

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15
Q

how long does it take an animal to develop antibodies

A

Takes awhile for animal to develop antibodies until 18months and antibodies rise over time and can’t be detected at low levels — around 3yrs when can be detected in blood

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16
Q

how long does it take for an animal to show clinical signs once infected

A

5-6 years with full blown Johne’s, likely affected as a young calf —> tip of the iceberg

17
Q

how is johne’s diagnosed

A

History (herd and individual level)

Clinical signs

Diagnostic tests

  • Serum ELISA (antibody)
  • Milk ELISA (antibody)
  • Fecal PCR (MAP)
  • Fecal smear (MAP)
  • Fecal culture (MAP)
  • PM and histopathology (MAP)
18
Q

how is johne’s diagnosed using ELISA testing using serology (screening)

A

Serology = plain tube

~50% sensitivity

False negatives possible

99% specific

But beware after TB test

  • False positives

Fluctuating antibody results possible

19
Q

how is johne’s diagnosed using ELISA testing using milk (screening)

A

Screened quarterly via milk recording

Less sensitive

False negatives and false positives

Provides basis for many dairy herd control programmes

20
Q

how is johne’s disease diagnosed using fecal PCR

A

detection of organism in feces

issue with light/intermittent shedding

Variable sensitivity 20-100% (excretion dependent)

21
Q

how is johne’s disease diagnosed using fecal smear ziehl-nielsen

A

False negative very possible

Look for clumps of acid fasts

22
Q

how is fecal culture used to diagnose johnes

A

‘Gold standard’

Can take several months

Expense (specialized media)

23
Q

how is johne’s treated

A

None

Isolate

Get clinical cases off farm ASAP

If BCS is not too bad and no edema possible to food chain

  • Remember other issues (vet medicines, withdrawals etc)
24
Q

what are the goals of controlling johne’s (4)

A
  1. to remain free from MAP
  2. to eliminate MAP from the herd as fast as possible
  3. to prevent the spread of MAP 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 the impact
25
Q

what tests are useful to establish herd status

A

Bulk tank ELISA:

  • Useful starting point in dairy herds but insensitive especially in low prevalence herds
  • False negatives

Blood serology:

  • 30 cow screen
  • Select based on age/ICSCC
  • All animals >2yr
26
Q

what are the 3 herd statuses on farm

A

1. not infected

to remain free from MAP

2. infected, low prevalence

to eliminate MAP from the herd as fast as possible

3. infected, moderate or high prevalence of infected animals

to prevent the spread of MAP to incoming stock (including homebred replacements) in order to reduce prevalence over time

27
Q

what are general control principles for a non-infected farm wanting to remain johne’s free

A

bioexclusion

28
Q

what are general control principles for an infected farm with low prevalence wanting to eliminate MAP from herd as fast as possible

A

bioexclusion

test and cull

29
Q

what are general control principles for an infected farm with moderate or high prevalence wanting to prevent spread of MAP to incoming stock in order to reduce prevalence over time

A

bioexclusion

test and cull

possibly breed to terminal sire initially

buy in replacements from accredited-free source, keep separate

30
Q

how do you test and cull using screening

A

ELISA-based:

  • Blood test all animals >2yrs old annually
  • Milk ELISA quarterly

Cull positives at convenient time

Manage positive cattle as ‘leper colony’

  • Beef cows in separate group
  • Dairy cows calve in separate groups
  • Don’t retain offspring for breeding

Johne’s accredited free = 3 x annual clear tests

31
Q

what is the CHeCS disease status accreditation

A

Level 1: there have been 3 clear annual herd tests. This is the lowest level of risk

Level 2: there has a current clear herd test, but has not yet gained level 1 status

Level 3: at the most recent herd test there are reactors in the herd at the level of 3% or fewer

Level 4: there has been more than 3% reactors at its most recent herd test

Level 5: those herds without a health plan for Johne’s disease and that do not adhere to the mandatory elements of the health plan are risk level 5. This is the highest level of risk and additionally applies to herds that carry out no testing

32
Q

how is johne’s controlled from a general management prespective

A

Calf rearing

Cleanliness

Colostrum

Replacement milk

Pasture/slurry

33
Q

how is Johne’s controlled in beef herds (5)

A
  1. Identify status of breeding cattle
  2. Separate into negative and positive groups
  3. Biosecurity: establish (herd-level) status of animals coming into herd
  4. Keep replacements from negative-test cows and from calves that have had less infection-pressure (ex. calves calved at grass)
  5. Slurry and/or manure management
34
Q

what are the difficulties to johnes control in beef herds

A

Less ability to manage transmission between infected dam/adults and young calves than dairy

Possibly increased chance of calves being exposed to other host (sheep/deer) as more likely to be outside during critical period (first month)

Environmental management probably most feasible (fencing off standing water etc)

35
Q

how is johnes controlled in dairy herds

A

as for beef plus:

Don’t pool colostrum in herds with known Johne’s disease from cows with unknown/positive test status

‘Herdwise’ testing scheme

36
Q

what is a herdwise testing scheme used in dairy johnes control

A

Quarterly individual milk antibody testing used as a tool to control the disease within a herd

Traffic light system is used to categorize cows, and inform management decisions about which milk to collect for replacement feeding and animals testing positive are put into separate calving facilities

All cattle are re-tested every 3 months when in milk, so deacons are less based on a single antibody result

Repeat positives are culled as they are likely to have reduced milk yield and will be contributing to environmental contamination

37
Q

what are the grades of milk ELISA testing

A
38
Q

what is the aim of grading cows based on milk ELISA

A

antibody results used to inform management decisions

Milk/colostrum for replacements = green

  • Group calving

Calving facilities = yellow

  • Individual

Culling repeat positives prior to next calving = red

  • Environmental contamination
  • Minimize milk and slaughter losses
39
Q

is there a vaccination for johnes

A

only available by import

Only available by import

Needs Animal Health Office approval

Interferes with TB testing

Does not stop cases

Should also use all aforementioned hygiene practices

Module 21: Ruminant Production (21 decks)

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