Caseous lymphadenitis is primarily an infection of sheep and goats. However, the bacteria that causes the infection can be spread to horses, cattle, camelids, wild ruminants, primates, pigs and birds. Corynebacterium pseudotuberculosis causes abcesses to occur in many different areas on horses. Also known as pigeon fever, pigeon breast, dryland distemper, dryland strangles, false strangles, caseous lymphadenitis and breastbone fever, C. pseudotuberculosis appears mostly in the western areas of the United States during the late fall.
According to the Colorado State University's Equine Science Department, C. pseudotuberculosis can live in the soil, be transmitted by flies or through contact with an infected animal. It enters the horse's body through broken skin, wounds, eyes, nose or mouth. The disease is highly infectious, easily infecting multiple horses on a single property. The bacterium in the pus drained from an infected abscess can live up to 55 days in faeces, hay, straw or wood shavings. The colder the temperature, the longer the bacterium can survive outside the body.
Early indicators of a C. pseudotuberculosis infection include fever, lameness, depression, lethargy and weight loss. Small, mild abscesses may be present. However, a severe case may present with multiple massive abscesses. The abscesses are generally located on the chest, midline, leg and groin area. However, the disease may take the form of internal abscesses, displayed by a slight swelling on the outside of the horse.
C. pseudotuberculosis is easily mistaken for distemper, strangles or other infections. According to the Merck Veterinary Manual, isolation of the bacterium within a lesion is necessary to confirm the infection. Samples can be taken from the abscess drainage or through punch biopsies.
The proper treatment ensures horse recovery from infection within a 77 day period. Hot packs are applied to abscesses to encourage opening and drained. Open abscesses should be regularly cleaned out and flushed with sterile saline. The veterinarian may choose to surgically lance the abscess if the capsule is especially thick. Ultrasounds aid in locating deep abscesses that present internally. Pain and swelling can be controlled through the usage of a non-steroidal anti-inflammatory drug, such as phenylbutazone. When abscesses are deeply internal, a prolonged treatment of procaine penicillin G is administered intramuscularly.
According to the Colorado State University's Equine Science Department, proper care must be taken to reduce infection on a premise. Pests should be controlled through proper cleaning and disinfecting of stalls, paddocks and pastures. Any containers used to collect pus should be disinfected or disposed of properly. Pus should never be drained directly onto the ground. Infected bedding, hay, straw or other stall materials should be removed and destroyed by burning. All utensils and tack should be disinfected. Infected horses should be quarantined away from healthy animals.