Understanding Corynebacterium pseudotuberculosis and Caseous Lymphadenitis
Caseous Lymphadenitis (CLA) is a chronic, debilitating infection of the lymphatic system. It is colloquially known as 'cheesy gland disease' due to the characteristic appearance of the pus found within infected nodes. While not always immediately fatal, it causes significant economic losses and welfare concerns. Unlike Blackleg, which is an acute clostridial infection, CLA is a slow-burning, persistent disease that challenges farm management.
The External Form: Lymphadenopathy and Abscessation
The external form is the most recognizable, presenting as swellings near the head and neck. These nodes, including the parotid, submandibular, and prescapular nodes, become firm and eventually undergo liquefactive necrosis. Once these rupture, they contaminate feeders and fencing. Similar to the inflammatory complications seen in Bovine Mastitis, the primary goal is preventing environmental contamination.
The Internal Form: Visceral Abscessation
The internal form is often silent, referred to as 'thin ewe syndrome' in sheep. Abscesses develop in the lungs, kidneys, and liver. Animals suffering from the internal form often show respiratory distress, similar to the pulmonary effects observed in advanced Caprine Arthritis Encephalitis (CAE). Because the symptoms are subtle, it is often misdiagnosed until necropsy.
Transmission Dynamics and Environmental Persistence
The bacteria enter the body through wounds caused by shearing equipment, ear tagging, or abrasive thorns. It is essential to note that CLA can spread horizontally within a herd. While not as rapidly contagious as Equine Influenza, it is highly stable in dry, dusty environments. Producers should note that secondary infections, such as those seen in Foot Rot (Livestock), can exacerbate the spread if hygiene protocols are neglected.
Diagnostic Approaches and Herd Screening
Veterinarians utilize physical examination and culture to diagnose active cases. Serological testing for antibodies is available but can be complicated by cross-reactivity. Unlike the rigorous quarantine protocols used for Equine Infectious Anemia (EIA), testing for CLA is often focused on identifying and isolating carrier animals.
Management Strategies: Culling and Control
Because antibiotics are ineffective at curing the condition, culling remains the gold standard for disease eradication. Infected individuals should be isolated immediately. Rigorous cleaning of shearing equipment is mandatory to break the cycle of infection. Vaccination exists, though it is often used as a control measure rather than a total preventative.
