An important part of responsible animal care is familiarizing yourself with some of the common health challenges your residents may face. If you care for small ruminants, caseous lymphadenitis (CL, or sometimes abbreviated as CLA) is one of the diseases you should take time to learn about because it is quite common in sheep and goats worldwide. By having a basic understanding of this disease, you will be able to provide the best care possible to CL positive individuals while also reducing the risk of transmission to other residents.
What Is Caseous Lymphadenitis?
Caseous lymphadenitis is a contagious and chronic disease that affects both sheep and goats, and is caused by the bacterium Corynebacterium pseudotuberculosis. C. pseudotuberculosis can also cause disease in other species such as cows, horses, llamas, and alpacas. The external form of CL manifests as abscesses in, or close to, peripheral lymph nodes, while the internal form manifests as abscesses in internal lymph nodes or internal organs. Sheep and goats can be affected by either form, but the external form tends to be more common in goats and the internal form tends to be more common in sheep.
Common sites for external CL abscesses include under or along the jaw, in the area below the ear, near the shoulder, or in front of the hind leg, though these are not the only areas they can occur. Pus from CL abscesses will be odorless and is usually very thick. In sheep, the pus is often white, while in goats it tends to have a greenish hue. Individuals with the external form rarely have other symptoms or become clinically ill. The internal form, on the other hand, typically causes chronic weight loss, with other symptoms depending on the area of the body affected. Lung abscesses, for example, can result in respiratory signs such as coughing, thick nasal discharge, and fever. Clinical signs of disease typically increase with age for both internal and external forms.
C. pseudotuberculosis spreads most often through discharge from external abscesses, though individuals with the internal form could spread the pathogen in their nasal discharge or while coughing. The bacteria can survive for two months on bedding, wood, and other fomites, and can survive for eight months in the soil. Individuals become infected if the bacteria enters the body through skin wounds and abrasions, or less commonly, via the mucous membranes.
CL should always be considered a possibility if a sheep or goat develops an unexplained abscess, but not all lumps are abscesses, and not abscesses are caused by C. pseudotuberculosis. If an individual has an external abscess, a suspected diagnosis can be made based on the location of the abscess and by observing the appearance and lack of odor of the pus. However, diagnostics are necessary to confirm that the cause is CL.
Though blood tests are available, a bacterial culture is necessary for a definitive diagnosis, which can make diagnosis of the internal form more difficult. Your veterinarian may recommend performing an ultrasound or radiograph to detect internal lesions, and depending on the location, further diagnostics may be recommended. Blood testing can be used as a screening tool for asymptomatic individuals, but false-negatives are possible and tests may not be able to differentiate between a true positive and a vaccinated individual (more on vaccination below). There are a few different blood tests available, so be sure to talk to your veterinarian or the diagnostic lab about what tests they offer and the limitations of the test.
Currently, there is no cure for CL, but your veterinarian may recommend certain treatments based on the form, location of lesions, and the severity of the disease. For individuals with external abscesses, your veterinarian may recommend surgical removal; lancing, draining, and flushing; or injecting medication directly into the abscess. Some studies suggest that injecting tulathromycin (Draxxin) into lesions can cause them to resolve without having to lance them. In some cases, systemic antibiotics may also be recommended, and depending on the size, location, and other interventions recommended by your veterinarian, an NSAID may be recommended as well. CL is potentially zoonotic, so be sure to wear gloves when working with someone with an abscess and carefully collect and dispose of any pus to prevent environmental contamination.
Treatment of individuals with the internal form of CL is highly dependent on location and severity. Your veterinarian may recommend a systemic antibiotic treatment such as tulathromycin or a combination of pencillin G and rifampin (penicillin on its own is not likely to penetrate a developed abscess).
Preventing Disease Spread
Because of the prevalence of CL, it is highly likely that sanctuaries that regularly welcome new sheep and goats will eventually have a positive resident. Therefore, it’s important to identify ways to prevent the spread of disease to other residents. Incoming individuals should be thoroughly checked for external abscesses and, as mentioned above, blood testing can be used as a screening tool, but make sure you talk to your veterinarian about the limitations of available tests. Because of the potentially long incubation period, repeat testing may be recommended.
Establish CL Positive And Negative Herds
Some sanctuaries choose to house positive and negative individuals in separate herds in order to lessen the likelihood of negative individuals being exposed to the disease. This may not be an option for everyone, especially smaller sanctuaries or those that only have one positive individual, but can be a good way to prevent disease spread. However, it is important to make sure you are offering both your positive and negative individuals with the same standards of care including ample space, an enriching environment (indoors and out), healthy social dynamics, and companionship.
You should still plan on isolating individuals with draining abscesses, and will need to take measures to prevent environmental contamination or spread via fomites, but by keeping positive individuals separate, the risk of exposing negative individuals to the bacteria will be reduced.
Reduce The Risk Of Exposure In Mixed Groups
If establishing separate herds is not feasible, it is possible to house positive and negative individuals together while still reducing the risk of disease spread. Because the disease primarily spreads through drainage from an abscess, in this situation your goal should be to ensure individuals are not exposed to anyone with a draining abscess and that their environment and objects they come into contact with do not become contaminated. Therefore, you must closely watch for external abscesses, making sure to isolate individuals before abscesses rupture. Individuals should be isolated prior to the abscess rupturing and should remain in isolation until the abscess has stopped draining and has healed over, but it’s important to remember that resolution of an abscess does not mean the individual no longer has CL, and they may develop more abscesses in the future.
If you care for CL positive individuals, talk to your veterinarian about the potential benefits of a vaccination program. While vaccination does not eliminate or cure the disease, it can offer your residents a certain degree of protection, and in CL positive individuals, vaccination can reduce the instance of clinical signs. Studies of sheep have shown that vaccination has resulted in fewer abscesses, and anecdotally, the same has been seen in vaccinated sanctuary goat residents.
There are commercial vaccines available, but it is important to only use them for the species they are labeled for- there have been instances of goats having severe reactions to CL vaccines labeled for sheep. According to Roberson, Baird, and Pugh, anecdotal information suggests that goats do better with autogenous CL vaccines (custom-made vaccines using samples from your sanctuary’s CL positive residents), rather than commercial vaccines, though adverse reactions are still possible and have been reported by at least one large sanctuary.
Other Preventative Strategies
In addition to establishing protocols aimed at identifying and isolating individuals with abscesses before they rupture, eliminating hazards in the environment that could result in skin trauma can also help reduce the chance of spread (though even minor breaks in the skin, such as those that result from headbutting, can be a point of entry of the pathogen).
If you work with a shearer who uses their own equipment, ask that equipment be disinfected prior to use on your residents, and make sure they know you value the individual’s comfort and safety over speed. If you are able to thoroughly check individuals for external abscesses prior to shearing, this will reduce the likelihood of accidentally rupturing an abscess during the shearing process. Some shearers may have concerns about shearing individuals in a CL positive herd, or may even flat out refuse, so it’s a good idea to have a conversation with them ahead of time. In the event that an abscess ruptures during shearing, equipment should be thoroughly disinfected prior to shearing anyone else.
Though CL is a chronic disease, individuals can live a long, happy life with it, especially if they only develop external abscesses. It’s important to provide all of your residents, including those who are CL-positive, with compassionate, individualized care while responsibly protecting other residents from becoming infected. Different strategies will work best for different sanctuaries, but the important thing is to understand how the disease is spread and enact protocols that reasonably reduce the risk of transmission.
Caseous Lymphadenitis Of Sheep And Goats | Merck Veterinary Manual (Non-Compassionate Source)
Sheep And Goat Medicine, Second Edition (Non-Compassionate Source)
Large Animal Internal Medicine, Fifth Edition (Non-Compassionate Source)
Caseous Lymphadenitis Of Sheep and Goats | Washington Animal Disease Diagnostic Laboratory (Non-Compassionate Source)