Caseous lymphadenitis
Caseous lymphadenitis is a chronic disease of sheep and goats. It is characterized by abscess formation in lymph nodes and sometimes in lungs and other organs. The causal organism is Corynebacterium ovis which is also known as Preisz Nocard bacillus. The organism is gram-positive coccobacillary and shows a beaded appearance due to the presence of metachromatic granules. It produces a toxin which is an important virulence factor. The organism also causes suppurative lymphangitis of cattle and horses, suppurative orchitis and epididymitis in rams and suppurative lesions in monkeys. The disease has also been observed in goats.

Transmission: The source of infection is the discharge from ruptured lymph nodes. Infection gains entry in the body through shearing wounds or through naval and docking wounds.

Symptoms: In sheep, there is an enlargement of one or more superficial lymph nodes like submaxillary, prescapular, prefemoral, supermammary and popliteal nodes. The abscesses commonly rupture and thick green pus is discharged. In rare cases chronic pneumonia, polynephritis and paraplegia may be present. Ulcerative lymphangitis occurs as a chronic infection in horses and rarely in cattle. Lymphatic vessels become enlarged; ulcers may develop and discharge purulent material.

Lesions: Caseous abscesses filled with greenish-yellow pus occur chiefly in lymph nodes and to a lesser extent in internal organs. Diffuse bronchopneumonia with more fluid greenish-yellow pus may be present.

Diagnosis: The nature of lesions and their distribution may be suggestive of infection with Corynebacterium ovis. Confirmatory diagnosis may be made at by isolation and identification of the organisms from the lesions.

Treatment: is not usually undertaken although the organism is sensitive to penicillin. Control: It depends upon elimination of all sheep with enlarged lymph nodes. Shearing and docking should be carried out in clean surroundings. All docking
implements and shears should be dipped in a strong disinfectant before their use.