What is JD?


Johne’s disease is an invariably fatal  disease of cattle, goats, deer, camelids and sheep.

Johne’s disease is caused by the  bacteria Mycobacterium paratuberculosis.  The bacteria grows in the intestine wall which becomes thickened and less  effective at absorbing nutrients from the food.

Features of the disease in cattle

  • Long incubation before signs develop — from 12 months to 15  years (in most cases, 3–5 years). It also takes a long time for an animal  infected as a calf to show up ‘positive’ using the current tests.
  • Fall in milk yield.
  • Diarrhoea which persists despite common treatments such as  worming, change of food.
  • There may be remissions( normal dung but then diarrhoea  commences again).
  • Loss of weight.
  • Emaciation.
  • Eventual death.
  • There may be several cases per year — up to 4% in very heavily  infected herds.
  • Production loss may be occurring in up to 5–10% of animals.

Survival of the bacteria

The bacteria which causes JD is very persistent, with the bacteria able to live for a period of up to 12 months on  the ground. Contamination of the ground must therefore be considered in any  control program.

Animals infected

In cattle, calves up to 30 days are very  susceptible and readily infected if exposed to the bacteria. They are still  susceptible up to 12 months — they do not often become infected after the first  year. In most cases, cattle are infected on their property of birth.

Spread of the bacteria

The most common method of  animal-to-animal spread is to the calf from its dam via germs on the udder.  Calves can also be infected by cross-suckling. Animals up to 12 months of age  may pick up infection from contaminated ground. Some calves may also be born  infected.

Because of the risk of infection —  before as well as after birth — all progeny of infected cows are highly likely  to be infected.
Milk from infected cows is also  considered a risk. Artificial insemination and embryo transfer are considered  very low-risk sources of contamination.

The most common form of spread from farm  to farm is via an infected animal (one generally showing no clinical signs).  Environmental spread has to be considered but is relatively uncommon.