Pigeon Fever is the common name for syndromes in horses caused by infection with the bacterium Corynebacterium pseudotuberculosis. This Gram-positive organism is a soil-dwelling microbe with a worldwide distribution, though it is more frequently seen in certain regions. The disease is primarily a concern for livestock, but the question of whether humans can contract this infection from horses is a valid health concern for those who work closely with equines. Understanding the nature of this bacterial infection is the first step in assessing any potential risk to people.
The Disease in Horses
In horses, infection with Corynebacterium pseudotuberculosis typically manifests in three distinct forms, with severity varying depending on the location. The most frequent form is the development of external abscesses, often found in the pectoral region or along the ventral midline. This accumulation of pus in the chest area historically led to the name “Pigeon Fever,” as the swelling resembles a pigeon’s breast. These external abscesses are usually well-encapsulated and contain tan, odor-free purulent material.
A less common, but more serious, manifestation is internal infection, where abscesses form within the thoracic or abdominal cavity, affecting organs like the liver or spleen. The third form is ulcerative lymphangitis, which involves severe swelling and infection of the lymphatic vessels, most often in the limbs. The bacteria persists in the environment, surviving in soil for many months, and cases are often seasonal in endemic areas.
Zoonotic Potential and Transmission
The central concern for horse handlers is the possibility of the infection passing from the horse to a human. While rare, this transmission is possible because Corynebacterium pseudotuberculosis is classified as a zoonotic agent. The primary route of infection is not through casual contact, but through direct inoculation of the bacteria into a break in the skin.
The highest risk occurs when a person has direct contact with the pus or drainage from an equine abscess. The bacteria is present in high concentrations within this purulent material and can readily enter the body through a cut, scrape, or abrasion. Exposure can also occur through contaminated soil, as the bacteria is a natural inhabitant of the ground and can survive there for up to eight months.
Contaminated flies, such as horn flies and stable flies, can also act as mechanical vectors, transferring the bacteria from an infected horse or contaminated surface. Human cases are infrequent and often linked to occupational exposure. The risk is predominantly associated with poor hygiene when managing open or draining abscesses in horses.
Symptoms and Human Manifestation
When a human contracts Corynebacterium pseudotuberculosis infection, the resulting condition is most frequently a localized infection known as lymphadenitis. This presents as swollen, tender, and painful lymph nodes near the site where the bacteria entered the body. Lymph nodes in the head and neck region are commonly affected, though any lymph node can become infected.
The localized infection can progress to form an abscess within the affected lymph node, which may need to be drained. Individuals may experience general symptoms, including fever, chills, and malaise. In extremely rare instances, the bacteria can spread beyond the lymph nodes, leading to a more severe, systemic infection involving internal organs or sepsis, particularly in individuals with compromised immune systems.
Diagnosis relies on culturing the bacteria from a sample of the pus or affected tissue. Treatment for localized lymphadenitis often involves surgical drainage or excision of the infected lymph nodes. Antibiotic therapy is generally used as a supplementary measure, as the thick capsule surrounding the abscess can limit the penetration of the medication.
Prevention for Horse Handlers
Horse handlers can significantly reduce their risk of contracting this infection by adopting consistent biosecurity protocols. The most effective measure is to minimize direct contact with pus from draining abscesses or with any contaminated soil or equipment. Always wear disposable gloves when examining or managing a horse with a suspected or confirmed case of Pigeon Fever, especially when treating an open lesion.
Proper wound care is also an important preventive step, involving covering any cuts, scrapes, or abrasions on your own skin before handling horses or working in the barn environment. Rigorous personal hygiene, including washing hands thoroughly with soap and water immediately after handling the horse, its equipment, or the surrounding area, must be a standard practice. The use of dedicated tools and equipment for the affected horse helps limit the spread of the bacteria within the stable environment.