Christine Navarre | 7/30/2018 9:50:07 PM
Caseous lymphadenitis, commonly referred to as CL, is a contagious disease of sheep and goats caused by the bacterium Corynebacterium pseudotuberculosis. It is manifested by abscesses of the lymph nodes and occasionally of the internal organs.
Caseous lymphadenitis is spread through contact with an infected animal or contaminated environment. Once in the environment, this bacteria can survive for long periods of time and infect other animals.
The disease can be found in any age animal, but the incidence increases with age in both sheep and goats. There are two forms of the disease: a superficial form and an internal (or visceral) form. The superficial form involves abscesses of the lymph nodes closest to the skin surface, most commonly affecting those around the head and at the origins of the limbs. The internal form involves abscesses of internal lymph nodes and organs and is usually associated with chronic weight loss and debilitation (“thin ewe” and “thin doe” syndromes). The superficial form is the most common. The following drawing indicates the common locations of abscessed lymph nodes seen in animals with caseous lymphadenitis.
The source of infection is discharge from ruptured abscesses. It can drain directly into the environment or onto other animals from superficial abscesses, or it can drain from lung abscesses into the airways and become aerosolized.
These bacteria can survive in the environment for months. Infection is more likely if there are breaks in the skin, but the bacteria can enter through intact skin or be inhaled. Examples of contaminated environmental sources that can continually transmit the organism include soil, shearing equipment, shearing shed boards, holding pens, hay and straw, plunge or shower dipping solutions and dust from contaminated sheds and yards.
The presence of abscessed lymph nodes and culture of C. pseudotuberculosis from the contents confirms the diagnosis of superficial caseous lymphadenitis. A blood test is available, but it is a better herd screening test than one for individual animals.
There are no antibiotics that can effectively penetrate the wall of the abscess, so treatment consists of lancing the abscesses or surgical removal of affected lymph nodes. These treatments are not a cure and abscesses can still occur later.
Any treatment attempts should be accompanied by adequate control measures to prevent spread. All affected animals should be immediately isolated, and options should be discussed with a veterinarian.
Once the animal is isolated, the abscess can be lanced, drained, and flushed daily with a disinfectant. The drained pus should be burned along with any contaminated bedding. Another option is lymph node removal, which reduces spread to the environment and to other lymph nodes in the animal’s body. This requires veterinary expertise due to dangers associated with anesthesia and dissection near large blood vessels and major nerves. It is expensive and does not guarantee a cure.
Control and Eradication
Eradication is very difficult and involves initial culling of all animals showing clinical signs followed by culling of all remaining animals that test positive using an enzyme-linked immunosorbent assay. (Pregnant females can be isolated and allowed to give birth before culling.) Couple the culling protocol with rigorous disinfection, removal of bedding and topsoil and isolation of uninfected individuals from the previously used areas for at least six months. Continue culling and repeat testing every six months to one year as directed by a veterinarian. Care should be taken not to reintroduce the disease through herd or flock additions.
Public Health Significance
C. pseudotuberculosis can infect people, especially those who are occupationally exposed, such as farmers, abattoir workers and shearers, but human cases are rare. Infection through breaks in the skin can be prevented by wearing disposable gloves when handling infected animals. Infection can also spread to people drinking raw milk from infected animals. Only adequately pasteurized milk should be consumed.
Christine B. Navarre, DVM, MS
School of Animal Sciences
Louisiana State University Agricultural Center
M.S. Gill, DVM, MS
Kate Camp, DVM