Understanding Caseous Lymphadenitis (CL) in Sheep and Goats

Caseous Lymphadenitis (CL), caused by the bacterium Corynebacterium pseudotuberculosis, is a chronic and highly infectious disease affecting sheep and goats worldwide. While prevalent on all continents, CL often goes underestimated, largely due to its non-reportable status in many countries, including the United States. This zoonotic disease poses significant economic losses to livestock industries due to various factors such as decreased marketability of breeding stock, condemnation of carcasses, and animal deaths. In this blog post, we will delve into the diagnosis, prevention, treatment, and biosecurity measures necessary to combat this debilitating disease.

Transmission

CL spreads primarily when Corynebacterium pseudotuberculosis enters the body through breaks in the skin after contact with pus from active abscesses. The bacteria may also spread less commonly through mucous membranes by inhalation or ingestion. Once established on a farm, CL is maintained largely through environmental contamination from draining lesions and infected animals. C. pseudotuberculosis can survive in the environment for up to 2 months on fomites such as bedding and wood and up to 8 months in soil, especially in the presence of organic material, shade, and moisture. This makes transmission possible through contaminated equipment, facilities, and other surfaces. It is important to note that CL is a chronic infectious disease, and infected animals may remain a source of infection within the herd or flock.

Clinical Signs

The presence of external abscesses, typically located in the region of peripheral lymph nodes such as beneath the jaw, near the ears, at the shoulder, or in the rear flank region, is often the first visible indicator of CL infection. These abscesses are important sources of disease transmission, particularly once they rupture and begin draining. Internal abscesses may also occur in lymph nodes and organs and are more commonly associated with chronic weight loss, ill thrift, and reduced productivity. If the lungs are affected, animals may also show cough, purulent nasal discharge, fever, tachypnea, and abnormal lung sounds. The incubation period generally ranges from 1 to 3 months. Some infected animals may appear clinically normal for a period of time despite carrying the bacteria.

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Testing options

Diagnosis of CL is based on clinical signs in addition to serology and PCR testing. Serology testing is a useful screening tool as a way to identify a potential problem early. To confirm that an abscess is CL, you can submit a sample of abscess content to Delta Livestock Diagnostics for polymerase chain reaction or PCR testing.

Unfortunately, there is no cure for CL, there is only prevention and management. When a potential abscess has been identified the following steps should be followed:

1. Isolate the animal from the herd immediately.
2. Place the infected animal on a surface that facilitates disinfection, like a concrete floor.
3. Wear gloves when draining abscesses to avoid contamination.
4. Use a disposable scalpel to cut and drain the abscess.
5. Thoroughly drain the abscess, collecting pus for lab analysis.
6. Clean the abscess cavity.
7. Keep the infected animal separated from the herd until fully healed.
8. Disinfect the area where infected animals were housed.
9. Maintain records of abscess cases.
10. Incinerate disposable items used during the procedure.

With the verified PCR results in hand, the producer can make informed decisions about their herd health.

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While CL has no effective treatment, certain management practices can minimize its impact:

1. Conduct frequent visual examinations of the herd, particularly in wool sheep and fiber goat breeds where abscesses may be hidden by long hair.
2. Avoid purchasing animals with visible abscesses or abscess scars.
3. Examine males before introducing them to the doe herd, as they can contaminate females.
4. Administer injections with new needles for every animal to prevent the spread of disease.
5. Disinfect equipment that may break the skin of animals, such as ear taggers, tattooing needles, and shearing equipment.
6. Cull infected animals to reduce the risk of CL infection.
7. Consider maintaining a closed herd to limit exposure to outside sources of infection.

Caseous Lymphadenitis is a chronic infectious disease of significant economic importance in sheep and goats. It can lead to abscess formation, chronic weight loss, carcass losses, and premature culling. Because the disease is difficult to eliminate once established, control depends on a combination of early recognition, laboratory confirmation, strict biosecurity, careful management of infected animals, and appropriate herd or flock health practices. These steps can help reduce the impact of CL on productivity and animal well-being.