Johne’s disease

Johne’s disease is a chronic progressive wasting disease caused by Mycobacterium Avium Paratuberculosis (MAP). The bacteria causing the disease are found in large numbers in the faeces and colostrum of clinically infected animals.

Animals are usually infected as calves (up to 6 months of age) but clinical signs are not usually seen for several years.

Clinical signs progress as the animal gets older:

• Gradual decline in milk production
• Loss of condition
• Classic watery, bubbly scour
• Bottle jaw and ventral oedema
• Death / culling

Because of the chronic nature of the disease, the clinical animal seen in the herd is just the tip of the iceberg. For every clinical case there may be as many as twenty subclinical cases which will go on to develop clinical signs. Some of these subclinical animals will be shedding bacteria in their faeces.

In the dairy herd, colostrum pooling is the major factor in the spread of disease.

There is a possible link with Crohn’s disease in humans and the UK dairy industry is starting now to look at reducing the incidence in the national herd.

Control programmes for eradication are the way forward for the future. There is already a demand in this country (especially Scotland) for accredited free stock and sooner or later we will have to catch up with Europe if we wish to continue to export. Several European countries are already starting Johne’s control programmes and eradication schemes. In Northern Ireland, Johne’s is a notifiable disease (like FMD).

There is a vaccine available but this is only suitable for use in herds with a very high incidence. Permission from Defra is also required before using this vaccine as there may be some cross reaction with TB testing.

The SAC runs an accreditation scheme as part of its Premium Cattle Health Scheme. Biobest runs an accreditation scheme in association with CHeCS.

Links:
www.sac.ac.uk/consultancy/pchs
www.defra.gov.uk/animalh/diseases/other/johnes.htm
www.biobest.co.uk/herdcare/index.html
www.checs.co.uk