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Further Johne's info

 

Johne’s disease

What is Johne's disease?

Johne’s disease (or paratuberculosis) causes an intractable scour and progressive loss of body condition in cattle.

In dairy cattle it may also be associated with a decline in milk production.

The pathological basis of the disease is a thickening of the intestinal wall due to the migration of inflammatory cells responding to the presence of the causative bacteria.

The organism multiplies to involve increasing lengths of intestine and the associated lymphoid tissues. This interferes with the normal functioning of the gut to induce a protein-losing enteropathy leading to the characteristic clinical signs.

Although primary infection usually occurs in the calf, clinical disease is not shown until the animal is three to five years old. However, in heavily infected herds disease may be seen in younger animals. 

The disease is eventually invariably fatal but infected animals are likely to be culled due to loss of production or welfare grounds. 

What causes Johne's disease?

The causative bacterium is a short, thick rod that is strongly acid and alcohol-fast and Gram-positive. 

The organism is found in characteristic 'clumps' of up to 30 organisms in faeces samples from clinical cases. 

These are most numerous in samples taken from an animal with advanced clinical disease ('high shedders'). Animals in the earlier stages may excrete far fewer organisms ('low shedders'). 

Colostrum and milk from infected animals may also contain organisms and in a small number of cases congenital infection of the foetus does occur.

The newborn calf is most susceptible to infection via the faeco-oral route and this susceptibility declines with age.

Other species affected

Although most often diagnosed in cattle, the disease is being increasingly recognised in:

  • sheep
  • goats
  • South American camelids.

The clinical picture is essentially the same although scour may not be so frequently recorded in sheep and goats.