Johne's Disease

Question 1

Causative agent of Johne’s

Answer 1

Mycobacterium avium subspecies paratuberculosis

Question 2

Route of transmission of Johne’s

Answer 2

Faecal-oral transmission
Infection acquired at young age via ingestion of faeces/milk from infected animals
In utero transmission has been reported but importance as a means of spread is unclear

Question 3

When do cattle typically present with Johne’s?

Answer 3

2+ years old

Some infected animals are sub clinical carriers so do not show signs but shed the mycobacteria intermittently.

Question 4

Clinical signs of Johne’s in cattle

Answer 4

Diarrhoea, initially intermittent but then persistent and profuse
Progressive weight loss without loss of appetite

Question 5

Post-mortem findings of cattle with Johne’s

Answer 5

Mucosa of terminal small intestine and large intestine usually thickened and folded in transverse corrugations
Enlarged and oedematous mesenteric and ileocaecal lymph nodes

Question 6

Clinical signs of Johne’s in sheep, goats and deer

Answer 6

Sheep and goats: diarrhoea is less marked than in cattle and may be absent
Deer: rapid weight loss, sudden onset of diarrhoea, death in 2-3 weeks or extreme emaciation developing over months without evidence of diarrhoea

Question 7

Postmortem findings of deer, sheep and goats with Johne’s disease

Answer 7

In sheep, thickening of mucosa may be less marked than in cattle, but necrosis and caseation may be present in regional lymph nodes
Lesions in deer are similar to those in sheep

Question 8

How should milk be treated to prevent transmission of Johne’s?

Answer 8

Should be pasteurised

Question 9

Describe the pathogenesis of Johne’s disease?

Answer 9

Bacterium = intracellular pathogen. Organisms cross the epithelial layer thorough the M cell route and interfere with the phagosome-lysosome fusion hence they survive.
Cell-mediated reactions are mainly responsible for enteric lesions.
As the disease progresses, granulomatous reaction develops I.e. accumulation of lymphocytes and macrophages in the lamina propria and submucosa.
The resulting enteropathy leads to loss of plasma proteins and malabsorption of nutrients and water.

Question 10

What is another name for Johne’s?

Answer 10

Paratuberculosis

Question 11

Terminal ileum of a cow with Johne’s. What are the circled structures?

Answer 11

Granulomatous inflammation

Question 12

Granulomatous formation in Johne’s is an example of what type of hypersensitivity?

Answer 12

Type IV

Question 13

What is the difference between Type I, II and III and then Type IV hypersensitivity?

Answer 13

Type I, II and III = antibody-mediated

Type IV = cell mediated

Question 14

How do you test for Johne’s?

Answer 14

Blood test for antibody to the MAP bacteria

Faecal test to identify the shedding/presence of MAP bacteria

Question 15

How does TB testing impact on Johne’s detection?

Answer 15

TB testing can result in a cross-reaction with antibodies to Johne’s
Therefore, either sample for Johne’s before TB testing, of 3 months after last TB test

Question 16

Why might a PCR of faeces from an infected animal return a negative result?

Answer 16

MAP bacteria may be intermittently shed, thus producing a false negative result for an animal that is infected with Johne’s

Question 17

Why might a blood test for antibodies produce a negative result for an infected cow?

Answer 17

Antibody response is variable and may be absent in the later stages of infection when the immune system becomes overwhelmed

Question 18

Is it a risk to spread slurry from a Johne’s positive farm onto silage fields?

Answer 18

Technically there is an increased risk, but if carried out properly, the ensuring process effectively kills MAP bacteria

Question 19

Can MAP survive on pasture and if so for how long?

Answer 19

Yes it can - sometimes for several years in cool damp climates and certain soil conditions

Question 20

What should you do if you have identified a Johne’s positive cow in the herd?

Answer 20

Ideally cull ASAP

Remove calf immediately after birth and pasteurise milk/feed it milk from a Johne’s-negative dam

Question 21

Which staining methods do you use to differentiate Mycobatceria from other bacteria?

Answer 21

Ziehl-Nielsen staining method (=a type of acid fast staining)

Question 22

Describe the M cell route of antigen sampling from the gut?

Answer 22

M cells overlying Peyer’s patches take up particulate antigens and deliver them to the subepithelial dendritic cells