Back from the Vet: Caseous Lymphadenitis in Goats
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Preventing the spread of contagious disease in livestock has become increasingly more important, as livestock owners strive to ensure the health of their charges. Insidious diseases such as caseous lymphadenitis are having increasing ramifications for health and production within herds. In order to appropriately manage a goat herd for this disease, it is imperative to understand the disease process as well as the current diagnostics available.
Caseous lymphadenitis is caused by bacteria, Corynebacterium pseudotuberculosis. This bacteria has two different groups. One that causes caseous lymphadenitis in sheep and goats, and one that causes pigeon fever in horses. While it is the same organism, they are of a different strain, or biotype. This bacteria can enter the body of a goat through any skin injury, from dehorning and castrating to a simple scratch. It can also enter the body across mucous membranes such as those in the mouth and airways. Inside the body, the bacteria have a predilection for infecting lymph nodes, but they can also infect the internal organs, such as lungs or liver. This infection can take several months to establish before forming the characteristic abscess. In animals where this abscess is in an external lymph node, like those around the throat or neck, it is termed the external form of caseous lymphadenitis. In animals who form abscesses in their internal organs, it is termed the internal form. Goats more commonly experience the external form of caseous lymphadenitis. The lymph nodes most commonly affected are those around the throat, such as the submandibular and parotid, and the superficial cervical in the shoulder area. Though goats less commonly have the internal form of disease, they can still have abscesses on their internal organs, such as the liver or lungs. These are much more difficult to identify. The abscesses caused by Corynebacterium pseudotuberculosis are characterized by their non-odorous discharge which may range from pasty to thick and chunky.
Corynebacterium pseudotuberculosis is a very hardy bacteria in the environment. This makes transmission easy, once the bacteria is present on a farm. Infected animals shed the bacteria from their abscesses. In the external form of caseous lymphadenitis, once the abscess matures, it will break through the skin and begin to drain. The draining material contains excessive amounts of bacteria which then contaminate the environment. Depending upon the conditions, it can survive up to eight months. It prefers areas with increased moisture, shade, and excessive organic material, such as manure. On hard surfaces, the bacteria can easily be inactivated with common disinfectants.
To definitively diagnose an animal with Corynebacterium pseudotuberculosis it is necessary to culture the bacteria within the abscess. However, if a goat has external abscesses, it should be highly suspicious for caseous lymphadenitis.
Often, animals with caseous lymphadenitis are very easy to identify, as the classic abscess of peripheral lymph nodes are readily seen bulging under the skin. Those with internal disease are much more difficult to identify. They can appear to be chronic poor doers, often with signs of pneumonia, as lung abscesses are common. As the animals age and the bacteria replicates, they are more likely to show signs of the disease. Animals with external disease can have abscesses break open and heal, however, they often recur. Any animal with an external abscess should be suspected of having caseous lymphadenitis, especially if it is found near a lymph node.
To definitively diagnose an animal with Corynebacterium pseudotuberculosis it is necessary to culture the bacteria within the abscess. However, if a goat has external abscesses, it should be highly suspicious for caseous lymphadenitis. In animals with internal disease, it can be difficult to identify the abscess for culture. In these cases, advanced imaging such as ultrasound and radiography can be helpful. One of the most common tests for caseous lymphadenitis is a blood titer test. While these tests can be useful in certain conditions, they should be used cautiously as a diagnostic tool. Titers can be affected by age of the animal, exposure to the bacteria, vaccination, and chronicity of infection. Animals with well-walled abscesses may have a low or negative titer, while vaccinated or exposed animals may have more elevated titers. In animals in which disease is suspected but abscesses cannot be identified, paired titer tests, two to four weeks apart, may be more useful than a single titer test.
Once an animal has been confirmed to have caseous lymphadenitis, it is imperative to control the infection within the herd. Ideally, the infected animal should be immediately removed from the herd. If this is not possible, isolation from the rest of the herd should be implemented immediately. If an animal is confirmed to be infected, but it is desirable to keep them in the herd, then treatment to control the disease is possible. However, it must be clear that treatment will only decrease possible shedding of the bacteria and slow the progression of disease. The most recent studies indicate that Draxxin can help resolve abscesses. This is not a labeled use of Draxxin and requires a veterinary prescription to be used legally. Even when using Draxxin, however, there is a high likelihood of recurrence of abscesses.
If an animal is confirmed to be infected, but it is desirable to keep them in the herd, then treatment to control the disease is possible. However, it must be clear that treatment will only decrease possible shedding of the bacteria and slow the progression of disease.
Control of caseous lymphadenitis within an infected animal is not nearly so imperative as control within the herd. The goal of any caseous lymphadenitis program should be elimination of the disease from the herd. Once caseous lymphadenitis is identified in an animal in your herd, working closely with your herd veterinarian will help establish the best plan for control and eradication. If the infected animals cannot be immediately removed from the flock, they should be isolated away from all healthy animals. Kids should also be removed from affected does and fed pasteurized colostrum or replacer. Care should be taken to keep medical and grooming equipment clean, and pens free from material that can cause injury to skin, as the bacteria can enter the animal’s system through even small defects. In instances of a widespread infection, it may be advisable to begin use of a caseous lymphadenitis vaccine. There are vaccines available for both sheep and goats. They should only ever be given to the label indicated species. While these vaccines can be helpful in control programs, they are not 100% effective at preventing the contraction of disease. They will also affect the use of titers to test for disease.
As with most diseases, prevention is much more preferable to control. If you are just beginning your goat herd endeavor, purchasing animals with low likelihood of disease is ideal. Animals should be purchased from herds that do not have disease and have negative blood titer tests. It is most preferable if the seller can provide negative titers for the entire herd. If you are unsure of the status of your herd, the best place to begin is with testing. While titer testing is readily available, care should be taken with interpreting results. For animals suspected to have caseous lymphadenitis, culture of a lesion is much more accurate. Working closely with your herd veterinarian can help you establish the status of your herd, and your intake process for new animals.
Sources:
Dr. Katie Estill DVM is a veterinarian consultant for Goat Journal, Countryside & Small Stock Journal, and Countryside online. She works with goats and other large livestock at Desert Trails Veterinary Services in Winnemucca, Nevada.
Originally published in the September/October 2020 issue of Goat Journal and regularly vetted for accuracy.
