Caseous lymphadenitis (CL) is a chronic, recurring disease in goats. A slowly enlarging, localized, and nonpainful abscess may develop either at the point of entry into the skin or in the regional lymph node (superficial or external form), from which it may spread via the blood or lymphatic system and cause abscessation of internal lymph nodes or organs (visceral or internal form). Initial infection may cause no clinical signs or may be accompanied by high fever, anorexia, anemia, and cellulitis at the infection site. Superficial abscesses enlarge and may rupture and discharge infectious pus.
This caseous (damaged or necrotic tissue; cheese-like) abscessation of lymph nodes and internal organs caused by Corynebacterium pseudotuberculosis occurs worldwide. It is an important endemic infection in regions with large sheep and goat populations. Economic losses result from reduced weight gain, reproductive efficiency, and wool and milk production, as well as from condemnation of carcasses and devaluation of hides. Although principally an infection of sheep and goats, sporadic disease also occurs in horses, cattle, water buffalo, wild ruminants, primates, pigs, and fowl.
Infection may occur after C pseudotuberculosis penetrates through unbroken skin or mucous membranes; however, in most cases it probably begins when superficial skin wounds are contaminated with purulent material from ruptured abscesses from other sheep and goats. Ruptured superficial and lung abscesses are the primary sources of environmental contamination. Contaminated dipping vats and shearing, handling, and feeding equipment are responsible for spread of the organism. The pus contains large numbers of bacteria that can survive for months in hay, shavings, and soil. The disease is commonly introduced into a flock by entry of an apparently healthy carrier from an infected flock, by contact on shared pastures, or via contaminated shearing equipment.
In housed goats and sheep, superficial abscesses develop mainly in the head and neck region due to transmission by contaminated feed, feeders, and other fomites. Animals with superficial abscesses show no obvious ill effects unless the location of the abscess interferes with functions such as swallowing or breathing. Abscessation may recur at the same site. Pulmonary, hepatic, and renal abscesses commonly cause “thin ewe syndrome.” Other manifestations include caseous bronchopneumonia, arthritis, abortion, CNS abscessation, scrotal abscessation, and mastitis. The visceral form is usually more extensive in sheep than in goats, with a preponderance of pulmonary involvement. The incidence steadily increases with age; clinical disease is more prevalent in adults, and up to 40% of animals in a flock can have superficial abscesses. In goats, the exudate is usually soft and pasty.