What is Pigeon Fever?
Pigeon fever, otherwise known as dryland distemper or Colorado strangles, is a highly contagious condition characterized by massive swelling in the pectoral muscles that gives a bulging appearance. While the name suggests an infection transmitted by birds, pigeon fever is instead thought to spread via flies, in particular cattle horn flies. Horn flies are persistent, tiny grey flies that feed on large mammals such as cattle, bison, buffalo, and horses. These insects are blood-feeders whose frequent, painful bites lead to infections such as mastitis (inflammation of the mammary glands), and conjunctivitis (pink eye) in their hosts. While cattle are primarily affected by horn flies, horses also fall victim to their attacks. These flies carry a specialized, resistant bacterium, Corynebacterium pseudotuberculosis, that leads to the formation of subcutaneous (beneath the skin) abscesses in cattle and equids. These large abscesses lead to the puffed-up appearance of the horse’s pectoral muscles. Though humans cannot catch pigeon fever, those who work with horses can easily transfer the infection from horse to horse by hand-body contact, or by using nonsterilized equipment that encountered fluid or drainage from an abscess. Bacteria from the abscess is then transmitted through the bite of the fly, which may cause a systemic or local infection. In and of itself, pigeon fever is not life-threatening; however, infections place any mammal at risk of tissue damage, bone infection, organ failure, even death. The horse should see the veterinarian for diagnosis of the abscess (bacterial culture), as well as controlled drainage to avoid sudden, painful rupture.
Horses are impacted by the disease in various ways, including visible swelling of the belly, chest, the groin, and the udders. Upon introduction of the infection, a horse may suddenly appear lame and stiff, and become reluctant to walk or exercise. In the absence of other symptoms, the horse’s condition often baffles horse owners who are unfamiliar with pigeon fever. Though the disease originated and has primarily affected horses in California, it is rapidly encroaching upon other areas of the United States such as Texas and the South. Alberta and British Columbia, Canada, have also experienced small outbreaks. Unfortunately, the associated bacterium, Corynebacterium pseudotuberculosis, is proving difficult to eliminate, a problem that is causing growing concern among the veterinary community.
Pigeon fever, otherwise known as dryland distemper or Colorado strangles, is a highly contagious condition characterized by a swelling of the pectoral muscles that gives a pigeon-like appearance.
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Symptoms of Pigeon Fever in Horses
- Swelling in pectoral muscles
- Visible large abscess that gives a pigeon like appearance
- Subcutaneous pus pockets
Pigeon fever has three types:
- External – The most common type causes abscesses on the chest and belly
- Internal – The bacteria affect the liver, lungs, kidneys and other organs, and internal abscesses may form
- Ulcerative lymphangitis – This type affects the lymphatic system, and poses the most serious threat to the horse; this type is rarely found in the U.S.
Causes of Pigeon Fever in Horses
- C. pseudotuberculosis enters cut, abrasion, fly bite
- Horn fly spreads bacteria from horse to horse
- Unsterile equipment used on infected and uninfected horses
- Hand to horse contact after exposure to infection
- C. pseudotuberculosis in soil
Diagnosis of Pigeon Fever in Horses
After an all over body evaluation, the veterinarian will assess your horse for skin condition. Blood tests may be suggested to rule out underlying disease or infection, and in order to assess organ function. Additionally, ultrasound has been found to be the best way to look for the source of infection. Veterinarians will run cultures on the pus to determine if the abscess is caused by C. pseudotuberculosis or another bacterium. Such testing helps to confirm cases in different areas of the country.
Treatment of Pigeon Fever in Horses
Veterinarians recommend the surgical lancing of the pus as opposed to letting the abscess rupture on its own. Controlled drainage is preferable because it allows for an examination and cleaning of the wound, culture and diagnosis, pain care, and the prevention of drainage entering the soil and infecting more horses. Penicillin and an anti-inflammatory will typically be administered to the horse. There is currently no vaccine for pigeon fever.
Recovery of Pigeon Fever in Horses
The caretaker’s primary responsibilities are to maintain a clean and sanitary wound site, flush the wound, disinfect and maintain a sanitary environment and equipment for the horse, and to develop a plan for better fly control. It is also particularly important for horse caretakers to frequently wash their hands, as well as wear disposable gloves when administering care to each horse.