Skip to main content
 
  • Share this page on Facebook
  • Print this page

Clinical Signs and Post-Mortem Lesions of OJD

Note Number: AG0971
Published: January 2006
Updated: November 2009

 

WARNING:

Some photos contained in this Agriculture Note could offend some readers. However, this graphical representation is necessary to allow for the accurate description of clinical signs and post-mortem lesions of ovine Johne's disease.

 

This Agriculture Note describes the clinical signs and post mortem lesions of ovine Johne’s disease.

Ovine Johne’s disease (OJD) can be mistaken for internal parasites, under-nutrition, or poor dentition. However, unresponsive or unexplained wasting and death in adult sheep, particularly in the spring, should arouse suspicions of OJD. Typical post mortem lesions of OJD include a thickened gut wall, enlarged, pale mesenteric lymph nodes, and dilated mesenteric and serosal lymph vessels.

Clinical signs of OJDAG0971-fig-1

Sheep infected with OJD eventually develop severe thickening of the gut wall. This reduces the ability to absorb nutrients. Weakness and ill thrift develop (Figure 1). These sheep tend to be found in the tail of a mob when driven. Scouring is not always a feature of OJD.

In long-affected (> 5 years) Merino flocks, OJD has killed more than 15% of adult sheep each year. Usually it takes several years between initial infection and the time that signs of the disease become obvious in a flock.

 

Post mortem findings

When looking for OJD, sheep suspected of having OJD, are slaughtered for necropsy examination. T ypical signs of OJD include a thickened gut wall, particularly the ileum, prominent mesenteric lymphatic vessels, and enlarged, pale lymph nodes (Figures 3 to 9). Samples are collected by a veterinarian or animal health officer and submitted to a laboratory for examination.

OJD is confirmed by microscopic demonstration of characteristic lesions and the presence of intracellular bacteria in the intestinal mucosa or local lymph nodes. Special stains are used to highlight the bacteria. If microscopic examination is inconclusive, culture of Mycobacterium paratuberculosis, from fresh tissues, will confirm the diagnosis. Mycobacteria are very slow growing and a result may take up to 4 months.

Specimen collection

For complete investigation, the following must be submitted to an approved laboratory:

  1. a specimen advice form, with full details of the history and post mortem findings,
  2. a clotted blood sample,
  3. a faecal sample, collected into a sterile container, for culture,
  4. divided samples of standard and suspicious tissues; one lot preserved in 10% buffered formalin for histopathology, the other lot kept fresh by chilling for tissue culture. The whole intestine and associated lymph nodes must be thoroughly examined for suspicious tissues. The standard tissues to be collected are:
  • any tissues with lesions suggestive of OJD,
  • the ileocaecal valve,
  • a 5 cm length of ileum immediately adjacent to the ileocaecal valve,
  • three 5 cm lengths of small intestine, at about 1 metre intervals from the ileocaecal valve,
  • two ileocaecal lymph nodes,
  • between two and four caudal mesenteric lymph nodes,
  • one piece of caecum, and
  • one piece of proximal colon.
Figure 2. Anatomy of the sheep gut

Figure 3. Image showing typical OJD lesions: thickening of the gut wall, particularly the ileum; enlarged mesenteric lymph nodes; and dilation of the gut lymph vessels.

Figure 4. Image showing gut from another OJD infected sheep. There is thickening of the ileum (1), an enlarged ileocaecal lymph node (2), enlarged caudal mesenteric lymph nodes (3) and serous atrophy of mesenteric fat (4

Figure 5. Image showing the gut of a normal sheep showing the thin, almost transparent wall of the ileum. The insert shows the thickened non-transparent wall of the ileum in an infected sheep.

Figure 6. Image showing the mucosal surface of the terminal ileum has been exposed showing the thickening of the wall. The insert shows a badly affected piece of gut on the left and a normal semi-transparent piece of ileum on the right.

Figure 7. Image showing the cut surface of an infected mesenteric lymph node. Note that it is a light pink and larger than normal and the cortex is wider than normal. The insert shows an infected mesenteric lymph node on the left and a normal lymph node on the right. The normal lymph node is smaller, has a thin white cortex and a darker medulla.

Figure 8.Image showing thickened lymphatic vessels, as seen here, are a common finding with OJD; in normal sheep they are usually difficult to see. The contents do not move readily when squeezed compared with normal lymphatic vessels which contain white lymph fluid.

Figure 9. The thickened lymphatic vessels often have a ‘string of beads appearance’ due to the thickening. Thickened lymphatic vessels are most prominent on the serosal surface of the ileum and caecum and the thickening usually extends all the way to the associated mesenteric lymph node, which may also be enlarged. The arrows point to some of the many thickened lymphatic vessels in the picture.

Further information

Further information about OJD can be obtained from animal health staff at your nearest DPI office or on the DPI web site: http://www.dpi.vic.gov.au/farming/OJD

 

Acknowledgements

This information note was developed by David Champness.  January 2006.

It was reviewed by David Champness, Animal Health Services. November 2009.

ISSN 1329-8062

Published and Authorised by:
Department of Primary Industries
1 Spring Street
Melbourne, Victoria

This publication is copyright. No part may be reproduced by any process except in accordance with the provisions of the Copyright Act 1968. 

The advice provided in this publication is intended as a source of information only. Always read the label before using any of the products mentioned. The State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication