Caseous lymphadenitis

Caseous lymphadenitis (CLA) is a chronic bacterial infection that primarily affects sheep and goats. It is caused by the bacterium Corynebacterium pseudotuberculosis. The disease is characterized by the formation of abscesses in the lymph nodes and internal organs, leading to significant economic losses in the livestock industry due to decreased productivity and increased culling rates.

Etiology

The causative agent of caseous lymphadenitis, Corynebacterium pseudotuberculosis, is a Gram-positive bacterium. It is a facultative intracellular pathogen that can survive and multiply within macrophages. The bacterium enters the host through skin wounds or mucous membranes and spreads to the regional lymph nodes.

Clinical Signs

The clinical signs of CLA vary depending on the location of the abscesses. In the external form, abscesses are typically found in the superficial lymph nodes, such as the submandibular, prescapular, and prefemoral lymph nodes. These abscesses are often visible and palpable. In the internal form, abscesses may develop in internal organs such as the lungs, liver, kidneys, and spleen, leading to more severe systemic signs such as weight loss, decreased milk production, and respiratory distress.

Diagnosis

Diagnosis of CLA is based on clinical signs, bacteriological culture, and polymerase chain reaction (PCR) testing. Fine needle aspiration of abscesses followed by culture and identification of Corynebacterium pseudotuberculosis is a common diagnostic method. Serological tests such as the enzyme-linked immunosorbent assay (ELISA) can also be used to detect antibodies against the bacterium.

Treatment and Control

Treatment of CLA is challenging due to the intracellular nature of the bacterium and the thick, caseous material within the abscesses. Antibiotic therapy is often ineffective, and surgical drainage of abscesses is commonly performed. Control measures include strict biosecurity practices, culling of affected animals, and vaccination. Vaccines are available and can reduce the incidence of the disease but do not provide complete protection.

Prevention

Preventive measures are crucial in managing CLA. These include:

• Implementing strict biosecurity protocols to prevent the introduction and spread of the bacterium.
• Regularly inspecting animals for signs of abscesses and isolating affected individuals.
• Maintaining good hygiene and wound care practices to reduce the risk of infection.
• Using vaccination programs to enhance herd immunity.

Economic Impact

Caseous lymphadenitis has a significant economic impact on the livestock industry. The disease leads to reduced productivity, increased veterinary costs, and higher culling rates. Infected animals may have reduced growth rates, lower milk production, and decreased wool quality. The presence of abscesses can also result in carcass condemnation at slaughter, further increasing economic losses.

See Also

• Sheep diseases
• Goat diseases
• Bacterial infections in animals
• Livestock management