Is Caseous Lymphadenitis Contagious to Humans?
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CL can be found all over the world and affects many animals, but is caseous lymphadenitis contagious to humans?
Caseous lymphadenitis (CL) is a chronically infectious disease in goats (and sheep) caused by the bacterium Corynebacterium pseudotuberculosis. It affects the lymphatic system and causes abscesses on the internal organs and lymph nodes, as well as superficial (external) abscesses. It can be found all over the world and affects animals as diverse as cows, pigs, rabbits, deer, horses, cattle, llamas, alpacas, and buffalo. But is caseous lymphadenitis contagious to humans?
The primary mode of infection is through direct contact with pus or other secretions from abscesses that contain the bacteria or by coming in contact with contaminated equipment (feed and water troughs, facilities, pastures). Goats become infected when the bacteria enter through an open wound (such as a nail scratch or combat injury) or mucous membranes (eyes, nose, mouth).
When external abscesses rupture, they release huge amounts of bacteria onto the skin and hair, which results in contamination of the immediate environment. The CL bacteria can exist in contaminated soil for a long time, in some cases over two years.
CL does not pass in semen, vaginal fluids, or saliva, and not in milk unless abscesses are present in the udder. External abscesses are frequently, but not always, adjacent to lymph nodes. Most often, abscesses present on the neck, jawline, under the ears, and on the shoulders. Incubation periods range from two to six months. Left untreated and allowed to run rampant, herd morbidity rates can reach 50%.
Older animals (four years and older) more frequently experience CL abscesses. Lactating does can transmit CL to their kids through milk if a CL abscess is found in the mammary gland.
CL abscesses must be treated to prevent further contamination of other animals as well as facilities and environments. Determine whether an abscess is caused by CL to rule out other disease processes that mimic CL, such as intestinal parasites or Johne’s disease. Take a sample of the pus to a lab for analysis.
Meanwhile, practice strict biosecurity. Isolate the animal from its herdmates until its external abscesses heal. Clean all environmental areas and disinfect with bleach or chlorhexidine. Burn bedding, loose feed, and other waste.
Unfortunately, there is no cure for CL in goats, and antibiotics are ineffective. A toxoid vaccine (made with killed germs) for controlling CL is available for sheep and seems to be effective in decreasing both the incidence and severity in flocks, but is not approved for use in goats and does not appear to prevent CL in caprines. A vaccine to prevent CL in goats was permanently withdrawn from the market in 2021.
According to the Ohio State University Sheep Team, “Autogenous vaccines (vaccines made from bacteria strains isolated from a specific herd) are another source of available immunization in sheep and in goats. However, a reputable, certified laboratory must produce the vaccine. Before using an autogenous vaccine, test it in several animals for adverse side effects. Goats seem to be more sensitive to the side effects of these types of vaccines.”
Once infected, an animal is a carrier for life. External signs of infection (in the form of abscesses) can appear within two to six months, but internal abscesses (which can affect many organs, including lungs, kidneys, liver, mammary glands, and spinal cord) can spread invisibly. The external abscesses are responsible for disease transmission, but internal abscesses can be fatal.
However, while CL is not curable in goats, it is manageable and considered mostly a nuisance disease. Infected animals should be quarantined and treated but not necessarily culled unless the animal is too sick to save.
The best means of prevention is avoidance (keeping the infection off the farm) through a closed herd. If bringing in new animals, avoid goats with swollen glands, and always put a new animal in quarantine for two months. Animals with CL should be isolated immediately. Goats infected with CL should be milked last, and all equipment cleaned and sanitized after use. Severely ill animals may have to be culled.
Some people have used unauthorized treatments for CL, such as injecting 10% buffered Formalin into the abscesses. However, it should be noted these treatments are unofficial and off-label. If the condition is misdiagnosed — if the abscesses are NOT caused by CL — then such treatments can do far more harm than good. It’s always best to involve a veterinarian if you believe your animal has CL.
Is Caseous Lymphadenitis Contagious to Humans?
Yes. CL is considered zoonotic, and humans can get CL through exposure to infected animals. The mainstay of (human) management is the surgical removal of affected lymph glands as well as antibiotic therapy.
Fortunately, goat (or sheep)-to-human transmission is rare. Australia has millions of sheep and perhaps as many as two dozen cases of transmission to humans each year (statistics vary). However, it’s worth noting the transmissibility may be underestimated because CL is not a reportable disease in many countries, including the United States.
The best preventative for avoiding goat-to-human transmission of CL is personal protective equipment (PPE). Prior to the coronavirus pandemic, few people saw the need to keep PPE on hand. That attitude has largely changed, and now PPE is far more common in homes. On the farm, use PPE (including gloves, long sleeves and pants, and shoe coverings) when handling zoonotic conditions with livestock.
Most animal-to-human transmission of CL occurs through skin-to-skin contact, which is why gloves and long sleeves are crucial. CL is not considered an airborne disease, though wearing a mask while handling sick animals is always wise. The chances of contracting CL from a sick animal while wearing PPE are extremely low.
Like any bacterial infection, the symptoms of CL in humans include fever, headaches, chills, and muscle aches. If the infection is especially severe and left untreated, symptoms could worsen to include abdominal pain, vomiting, jaundice, diarrhea, rashes, and even worse. It goes without saying that you should seek immediate health care if these symptoms are present, especially if you suspect you came in contact with CL.
Having said that, you should neither panic nor ignore a caseous lymphadenitis outbreak. Work with a veterinarian and take precautions to contain the spread of the disease among your herd and to prevent zoonotic transmission to humans. While the best treatment is prevention, sensible management practices just might save your herd.
Originally published in the May/June 2023 issue of Goat Journal and regularly vetted for accuracy.