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Y3 Infectious diseases > Johne’s disease > Flashcards

Johne’s disease Flashcards

1
Q

What is the name of the bacteria which causes Johne’s disease?

A

Mycobacterium avium subsp paratuberculosis

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2
Q

Give some features of the Mycobacterium avium subsp paratuberculosis bacterium

A
  • Slow growing, fastidious acid fast bacillus
  • Long lived in the environment
  • Weak host specifity strains
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3
Q

Describe the pathology of Johne’s disease

A
  • Organisms localises within the submucosa and mesenteric lymph nodes of the terminal SI and LI
  • Inflammatory response with the accumulation of more macrophages and lymphocytes
  • Granuloma formation in distal ileum & LN
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4
Q

Describe the gross changes in the GI tract of cattle with Johne’s disease

A
  • Diffuse thickening of distal ileum and colon due to fibrous tissue
  • Thick, corrugated intestine: impaired absorption, leaky gut
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5
Q

How do the gross changes in the gut affects its function?

What are the consequences of this?

A

Impaired mucosal barrier function, malabsorption (& consequently diarrhoea), protein losing enteropathy (& consequently muscle wastage, hypoproteinaemia, oedema)

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6
Q

How do you diagnose a clinical case of Johnes?

A
  • Has lost immune control: Likely to be ab +ve
  • Infectious: Organism in faeces
  • ELISA (Sens 85 – 95%)
  • Faecal culture
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7
Q

Describe the key points of Johne’s disease

A
  • Chronic
  • Spread within the herd
  • Faeco-oral transmission
  • Long incubation period but a short latent period: causes problems as animals are shedding the disease without having signs of it
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8
Q

What are the signs of clinical disease with Johnes?

A
  • Affects older animals (more than 3 years)
  • Often after calving due to stress
  • Profuse diarrhoea
  • Weight loss
  • Bottle jaw (swelling)
  • Animal remains bright and eating
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9
Q

What is the major transmission route of Johnes?

A

Faeco-oral

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10
Q

How does Johne’s affect productivity?

A
  • Less milk production
  • 5x more likley to be lame
  • more likely to develop mastitis and high SCC
  • more likely to suffer with digestive/respiratory disease
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11
Q

What are some risk factors for Johne’s?

A
  • Age: resistance to infection increases with age
  • Genetics
  • Herd management
  • Soil type
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12
Q

What are the two types of Mycobacterium avium subsp paratuberculosis ?

A

the slow-growing type I (or S for sheep) and the faster growing type II (or C for cattle)

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13
Q

How can animals be infected with Mycobacterium avium subsp paratuberculosis but not infectious?

A

Cell mediated immune response is protective and halts disease progression. If this falls then the bacteria proliferate and the animal becomes infectious

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14
Q

What are the 4 stages of clinical progression for Johne’s disease?

A
  1. Silent infection
  2. Subclinical disease
  3. Clinical disease
  4. Advanced disease
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15
Q

Describe a silent infection with Johnes

A

No clinical signs, but animals may shed bacteria. Tests will not detect, but faecal
culture may be successful (very low sensitivity at this stage)

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16
Q

Describe clinical disease with Johnes

A

Typically, only occur after 2 years of age. Gradual loss of body weight, but
normal or even increased appetite. A drop in milk production usually occurs the lactation before intermittent diarrhoea develops.

17
Q

Describe advanced Johne’s disease

A

Typically not seen on farms as affected cattle are culled for other, possibly
associated, reasons such as infertility or mastitis.
Emaciation, intermandibular oedema and “pipe stream” faeces

18
Q

What tests can be used to detects Mycobacterium avium subsp paratuberculosis

A
  1. Faecal culture (blood and milk also possible)
  2. Serology (ELISA)
  3. PCR
  4. Stained faecal smears
  5. Tissue biopsy
  6. Postmortem examination
19
Q

How can test accuracy for Mycobacterium avium subsp paratuberculosis be increased?

A

Increase the amount of testing as specificity is much higher than sensitivity

20
Q

How are newborn calves affected with Johnes?

A
  • Trans-placentally

- From the dirty environment or dam faeces (faeco-oral)

21
Q

How can Johne’s be controlled?

A
  • Prevent new infections in calves
  • Test & Cull
  • Test & Manage
  • Improved Farm Management (IFM)
22
Q

When purchasing new stock, how can you prevent introducing Johnes?

A
  • Buy from clean herds with no history of disease
  • ELISA the whole herd
  • ELISA individual animals (not ideal)
  • Faecal culture individual (not ideal)
23
Q

How might TB testing affect Johnes testing?

A
  • TB test will give “false +ve” to Mycobacterium avium subsp paratuberculosis ELISA test - ensure 60 day time lag between TB test & ELISA

Y3 Infectious diseases (19 decks)

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