Johnes Disease

Johne’s Disease (Paratuberculosis)

Johnes's disease (Paratuberculosis) is a chronic enteritis of adult cattle and sheep caused by Mycobacterium avium subspecies paratuberculosis (MAP). The main signs in cattle are progressive weight loss and chronic diarrhoea. Diagnosis and control are difficult. If your herd has no history of Johne's disease it is critical that all measures are taken to prevent introduction of infection because eradication of disease once prevalent in the herd proves very costly and may take many years.

There is limited but disputed evidence that the organism may be associated with Crohn's disease in humans.

Causes

The disease occurs worldwide, but especially in temperate climates, and affects particularly cattle, sheep, goats and deer reared in intensive systems. Many wildlife, including rabbits, and exotic species are also susceptible to Johne's disease.

There is evidence for intrauterine infection of the developing calf in the case of heavily-infected dams.  The disease is also transmitted to young calves by ingestion of the organism in colostrum, and from the faeces of infected animals contaminating food and surface water/water troughs, and the cow's teats.  There is a long incubation period and clinical disease is not usually apparent until three to five years-old although younger cases are possible. Infected animals may shed organisms in the faeces for over a year before clinical signs appear.

Early Clinical Signs

Farmers should look for diarrhoea, poor milk yield and weight loss in cattle three to five years-old with onset often following calving or other stressful event (sale, transportation etc). There is no fever and the animal maintains a good appetite until the terminal stages. Clinical signs may continue for several months with the cow/bull becoming emaciated, and then being culled for economic/welfare reasons.

Control and Prevention

There is no single reliable test for confirming Johne's disease during the early stages of disease (test described as having a low sensitivity).

Blood tests detect antibodies to crude M.paratuberculosis antigen but not all cases have a detectable antibody response.  In practical terms diagnosis is best done using a combination of serology (blood tests) and faecal examination for the causative organism.

Control

Control is difficult because of the long incubation period, shedding of infection by animals before they show clinical signs, and diagnostic techniques with poor detection rates in the early stages of disease.

Eradication requires a substantial commitment by the farmer, veterinarian and local laboratory and is based upon the identification and removal of infected animals. Blood testing and/or faecal examination may be done every 6-12 months with slaughter of positive cases.  Two consecutive herd negatives may indicate eradication.

Practical control measures that can readily be adopted to limit losses in a diseased herd include:

  • Rapid culling of diseased animals.
  • Minimise faecal contamination of food, water and pasture e.g. by raising feed and water troughs, strip grazing, use of mains/piped water rather than surface/pond water, avoiding spreading yard manure on pasture, and maintaining good hygiene in buildings/yards and calving boxes in particular.
  • Separate newborn calves from dams at birth and rear by bucket with artificial colostrum/milk (only possible for dairy calves).
  • Do not feed waste milk to calves
  • Do not raise calves from known infected dams as breeding replacements.
  • Re-stock only from accredited herds especially bulls.

Welfare Implications

There is no effective treatment and animals must be culled as soon as the diagnosis is confirmed.  It would be prudent not to keep the progeny of infected cows as breeding replacements.  Such offspring will generally fatten normally as clinical disease is unusual before year two.

General Recommendations for Veterinary Surgeons

Determine which of the herds in your practice has cows with Johne's disease. If the herd is found not to be infected, discuss with your clients the merits of joining a national herd test-negative Johne's disease program/scheme.

Emphasize the importance of biosecurity measures to help prevent your clients' herds becoming infected though purchase of cattle.

Summary

  • Keep clinical cases and Johne's test-positive cows out of the calving accommodation/pens.
  • Clean the calving accommodation/pens often.
  • Remove the calf from the calving accommodation/pens within one hour after birth.
  • Feed each calf four litres of colostrum before the calf is 6 hour-old.
  • Cow's teats should be prepped before colostrum collection to limit faecal contamination.
  • Colostrum should be fed from one test-negative cow to one calf.  The cow that donated the colostrum should be recorded on the calf's health record card.
  • After colostrum, feed only milk replacer or on-farm pasteurized milk.
  • Rear calves well away from adult cattle ensuring no contact with slurry or contamination of water or feed with faeces/slurry.