Acquired immunity after primary caseous lymphadenitis in sheep

Area of Science:

• Veterinary Immunology
• Bacterial Pathogenesis
• Sheep and Goat Diseases

Background:

• Caseous lymphadenitis (CLA) is a significant worldwide disease in sheep and goats, caused by Corynebacterium pseudotuberculosis.
• CLA is characterized by pyogranulomas in lymph nodes and lungs, posing challenges for disease control.
• Vaccination strategies for CLA remain controversial, despite the availability of some commercial toxoid vaccines.

Purpose of the Study:

• To investigate the efficacy of acquired immunity in controlling CLA.
• To determine the effect of a primary infection on subsequent challenge exposure to Corynebacterium pseudotuberculosis.
• To provide experimental support for the development of more effective CLA vaccines.

Main Methods:

• Adult seronegative ewes were used in the study.
• Primary inoculation with a streptomycin-sensitive strain of C pseudotuberculosis was administered to the external left ear.
• Ewes were subsequently challenge-exposed with a streptomycin-resistant strain (19R) in the right ear.

Main Results:

• Primary infection with at least 10(7) viable bacteria induced strong protection against challenge exposure.
• Ewes with primary infection did not develop lesions upon challenge, unlike immune-naive controls.
• Immune-naive ewes developed numerous pyogranulomas in the challenged ear, draining lymph nodes, and lungs.
• Ewes with primary infection, however, remained carriers of the disease.

Conclusions:

• Acquired immunity from primary infection confers significant protection against CLA challenge in sheep.
• The study model demonstrates that sheep with primary infection can serve as positive controls for vaccine efficacy testing.
• Further development of effective vaccination strategies is crucial for controlling CLA in sheep and goats.