Caseous Lymphadenitis (CLA)
Caseous lymphadenitis (CLA) is a bacterial disease of sheep and goats caused by Corynebacterium pseudotuberculosis. This organism belongs to a family of related bacteria, several of which are pathogenic for man and/or animals. Once an animal becomes infected with C. pseudotuberculosis, the bacterium is able to survive and replicate within cells of the immune system that would normally be associated with the killing of invading bacteria.
The infection leads to the formation of the lymph node abscesses with fibrous capsules which are typical of CLA. When superficial lymph nodes are affected these abscesses are visible as swellings beneath the skin, which may rupture and discharge pus. These abscesses can also act as reservoirs for the spread of bacteria to other sites within the body, most notably the lungs. Current treatment of diseased animals is limited as antibiotics cannot penetrate the pus-filled swellings effectively.
C. pseudotuberculosis can survive in the environment for several months and is highly infectious. Monitoring of disease status is compounded by the fact that animals may be infected without showing obvious clinical symptoms. As there is neither a commercially available diagnostic test nor vaccine for CLA in the UK at the moment, existing control of the disease depends on good management and strict quarantining of animals being brought onto farms. In addition to CLA, C. pseudotuberculosis also causes infections in horses (caseous lymphangitis) and mastitis in dairy cows.
Research at Moredun has determined the relationships between UK C. pseudotuberculosis strains and those from across the world. Significantly, all strains have been shown to be highly-related, suggesting that common control measures may be effective.
The development and commercialisation of a CLA diagnostic blood-test in conjunction with SAC has been a major achievement, providing a powerful tool to allow the identification of animals with CLA. Concurrently, preliminary assessment of several experimental vaccines has been undertaken. The results of these studies have been significant in that they have confirmed that better alternatives to currently available CLA vaccines exist.
In addition to continuing existing efforts to understand the mechanisms by which C. pseudotuberculosis causes disease in sheep, future work will seek to develop our experimental vaccines further in an effort to realise the potential for control of CLA in the UK.
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