Caseous lymphadenitis (CL) is a chronic bacterial disease that primarily affects small ruminants, such as goats and sheep, and is found globally. The infection is caused by the bacterium Corynebacterium pseudotuberculosis, a hardy organism capable of long-term survival in the environment. This disease is characterized by the formation of abscesses in the lymph nodes and internal organs of the affected livestock. Given the disease’s high prevalence in goat populations and close contact between animals and humans, CL has the potential to cross species lines.
Understanding the Zoonotic Risk
CL is recognized as a zoonotic disease, meaning humans can contract it from goats, although human cases are uncommon. The bacterium, Corynebacterium pseudotuberculosis, is a facultative intracellular pathogen, meaning it can survive and multiply inside host cells, which makes it challenging to treat. Transmission usually occurs when the bacteria enters the human body through a break in the skin, such as a cut, scratch, or abrasion.
The most common route of infection is direct contact with pus or drainage from an infected animal’s ruptured abscess. This material contains high concentrations of the bacteria and can contaminate the environment, including soil and equipment. People in occupations that involve frequent, close interaction with infected goats, such as farmers, veterinarians, shearers, and slaughterhouse workers, face the highest risk of exposure. A less common route of human infection is the consumption of raw, unpasteurized milk from an infected animal.
Signs of Infection in Humans
When a human contracts C. pseudotuberculosis infection, the typical presentation is a localized infection that is generally milder than the disease seen in goats. The infection most often presents as lymphadenitis, which involves the swelling and tenderness of one or more lymph nodes. These swollen nodes can form abscesses, which are painful and filled with pus.
The lymph nodes most commonly affected are those closest to the site where the bacteria entered the body, such as the nodes in the neck, armpit (axillary), or groin (inguinal). Systemic infection, where the bacteria spreads throughout the body causing severe symptoms like fever, chills, and organ abscesses, is extremely rare and primarily a concern for immunocompromised individuals.
Preventing Human Exposure
Minimizing the risk of C. pseudotuberculosis transmission requires consistent biosecurity measures when handling goats. The use of personal protective equipment (PPE) is paramount, especially when working with animals known or suspected to have abscesses. Handlers should wear disposable gloves, and ideally, protective clothing and eye protection when draining abscesses or handling potentially contaminated materials.
Contaminated materials, such as pus, bandages, or disposable gloves, must be properly disposed of, often through incineration, to prevent environmental contamination. Strict hygiene protocols are also necessary, including thorough handwashing with soap and water after any contact with goats, their housing, or equipment. Because the bacteria can survive in the environment for months, proper management of the animal’s surroundings is important. This includes regularly disinfecting equipment like tattoo tools and ear taggers, and cleaning barns and pens to remove organic debris that could harbor the bacteria.
Diagnosis and Management
If a person who has had goat contact develops a swollen, painful lymph node, they should seek medical attention and inform the provider about their animal exposure history. Diagnosing human CL involves a medical evaluation, which may include culturing the bacteria from the pus of an abscess or an affected lymph node. Identifying the specific bacterium, C. pseudotuberculosis, is crucial for confirming the infection.
Management of human CL typically involves a combination of treatment methods. Surgical excision or drainage of the affected lymph nodes and abscesses is often the primary approach for localized infections. Antibiotic therapy is generally used as a supplementary treatment, but full recovery can sometimes be slow or the clinical course protracted.