Caseous Lymphadenitis (CL) is an infectious disease caused by the bacterium Corynebacterium pseudotuberculosis (C. pseudotuberculosis). CL is prevalent on all continents and is known to affect sheep, goats, horses, dogs, rabbits and deer. CL is a zoonotic disease, meaning that it can be transmitted from animals to humans.
The C. pseudotuberculosis bacteria enter the body through wounds, through inhalation, or by contact with contaminated equipment or enclosures. Once inside the body, the bacterium travels to all major organs via the bloodstream. An animal’s immune system will attempt to contain the infection, thus creating the most noticeable symptom of CL-- large, thick-walled abscesses containing a large amount of thick, yellowish-green pus. Abscesses are most commonly found on the head or neck, but can also appear in other areas; internal abscesses can also be present. External abscesses are more commonly found in goats, while sheep are more prone to internal abscesses. CL should be suspected in sheep with unexplained weight loss, or a chronic cough unrelated to a respiratory infection. There is a blood test for CL, but the results are not reliable, especially in younger animals, according to the Alabama Cooperative Extension System at www.aces.edu. At this time, the only way to definitely diagnose CL is through lab testing of the external abscess exudate. Internal abscesses are diagnosed at necropsy. The incubation period for CL is 2-6 months. Some animals are carriers, which means they are infected but do not develop any signs. Carriers can infect other animals although they appear healthy themselves.
Management of CL involves regularly checking animals for any lumps or swellings, quarantine of animals with abscesses, and having a veterinarian drain and test abscesses for the CL bacterium. Not all abscesses are caused by C. pseudotuberculosis, so having the exudate tested is essential to a correct diagnosis.
Treatment involves draining and flushing external abscesses. All materials used for treatment of CL abscesses should be burned, and infected animals should be quarantined until the abscess has completely healed. It is important to drain an abscess before it ruptures in the field and spreads the bacteria to pastures or fences. Goatworld at www.goatworld.com is a good source for more information on treatment and management of CL.
There is no cure for CL; therefore, it is important to ensure a herd does not become infected. Any prospective additions to the herd should be checked carefully for lumps or scars from previous abscesses. Male animals should be checked around the scrotal sac and females should have the area around the udder inspected because abscesses can be hidden in those areas. Avoid purchasing animals with a cough or unthrifty appearance, as these symptoms can be indicative of internal abscesses.