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Caseous Lymphadenitis (CLA)

CLA abscess head/neck of sheep
CLA abscess lung of sheep
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Caseous lymphadenitis (CLA) is a chronic bacterial disease of sheep and goats caused by the highly infectious bacterium Corynebacterium pseudotuberculosis. The disease is characterised by abscess development in the lymph nodes and other tissues, and is increasing in prevalence in the UK. 

CLA results in welfare issues and economic losses due to ill thrift and carcase trimming or (in severe cases) carcass condemnation at abattoir.  CLA may also increase susceptibility to other infections.

Affected animals often have visible lumps in the superficial lymph nodes i.e. those lymph nodes which can be accessed from the outside of the animal.  Most frequently in the UK, lymph node abscesses tend to be associated with the head and neck region.  Abscesses in this area can press on the oesophagus preventing normal rumination, leading to weigh loss.  It is generally held that infected animals remain infected for their entire lives, and as such sheep and goat producers must apply strict biosecurity measures to help prevent and control the disease.

CLA is found in most parts of the world where small ruminants are farmed, including Europe, Australasia, North and South America, Africa, and the Middle East.  Prevalence of infection increases with age and is more common in sheep kept under intensive management conditions.

Key Points

  • Caseous lymphadenitis (CLA) is a chronic bacterial disease of sheep and goats, characterised by abscess development in the lymph nodes and other tissues.
  • The disease is increasing in prevalence in the UK, resulting in welfare issues and economic losses due to ill thrift and carcase trimming or (in severe cases) carcass condemnation at abattoir.  CLA may also increase susceptibility to other infections.
  • The disease is caused by the bacterium Corynebacterium pseudotuberculosis; this organism is highly infectious and is able to survive for long periods of time in the environment, acting as a source of infection for other animals.
  • Although not often encountered in the UK, the CLA-causing organism can also cause infections in humans.  Care is required to minimise exposure to pus.  Infection is caused by the bacterium gaining entry to the animal through scratches or cuts in the skin; therefore, shearing/clipping can be a risk factor for this disease.
  • Abscesses in the lymph nodes often present as visible lumps around the head and neck region.  If these rupture, cheesy pus is released, containing millions of bacteria, which is the main source of infection for other sheep and goats.
  • The infection can also spread to other organs of the animal (e.g. liver and lungs).  In certain cases, abscesses may interfere with rumination, leading to chronic weight loss.
  • According to some researchers, animals with CLA lesions in the lung may spread the infection through coughing.
  • Antibiotic treatment is ineffective as the bacteria are ‘protected’ within the lymph node abscesses, which become surrounded by a tough fibrous capsule.
  • Sheep or goats displaying chronic abscesses should be isolated and subjected to immediate veterinary and bacteriological investigation.
  • Control measures should include strict biosecurity measures including: quarantining (of both animals and premises), screening of imported animals, the cull of infected animals and application of rigorous hygiene procedures.  Shearing equipment should be dipped in strong disinfectant or chlorine bleach before and after use.  Older animals should be handled last during routine procedures.

Research at Moredun

Moredun is currently not actively conducting research in this area.

Farming and Veterinary Outreach

For further Information about CLA please see Moredun Newssheet 6.5 – Caseous Lymphadenitis (CLA) in Sheep: