Pigeon Fever – Not just for Pigeons?
Late summer, a time for last chance for romance, BBQ’s in the fading light, and getting that last trail ride in before the fall and winter routine of the school year begins. It is also the time however, when we most commonly see Pigeon Fever in our equine companions. Also known as “Dryland Distemper”, pigeon fever is an infection of the lymph nodes caused by the bacteria Corynebacterium pseudotuberculosis. This soil-borne organism is common in dry arid regions like Lake County.
An infection is usually seen as swollen, abscessed pectoral lymph nodes which produce the characteristic “pigeon-breasted” appearance in affected horses. The infected nodes rupture and drain thick, tan-colored pus, leaving large open sores in the chest and between the front limbs. Abscesses can also occur along the belly and between the hind legs. You may even see a large flat swelling along the belly. This particular swelling is not an abscess, but edema: an accumulation of fluid in the tissues as a result of the local inflammation incited by the abscesses. Rarely, abscesses and sores can occur in other regions, such as within the abdomen or chest.
Affected horses are usually bright and alert but signs of systemic illness can be seen as well. These signs include anorexia (refusal to eat), fever, and lethargy. Varying degrees of pain and lameness can be seen depending on the size and location of the abscess present; occasionally deep infections will occur in the muscles of the shoulder and groin. This rare manifestation is often seen as non-specific lameness which does not originate from the lower limbs and does not respond to typical therapies.
The infection is transmitted to horses through scrapes and abrasions and by flies which carry the bacteria from the surrounding soil and manure, then infecting the horse when they bite. The bacteria are carried in the blood stream to the local lymph nodes where they multiply, resulting in cell damage and the formation of an abscess. This occurs 1-3 weeks after the actual infection. Barring complications, horses will usually recover completely within 2-4 weeks depending of the severity of the infection.
A small percentage of horses have developed internal abscesses following initial infection and apparent resolution. This is a rare complication and produces non-specific symptoms which will vary according to where the abscess has developed. Signs that can be seen may include gradual weight loss, loss of appetite, fever, lethargy, and signs of respiratory or gastrointestinal illness. These symptoms are nonspecific and seen in many other disease conditions so consult with you veterinarian if your horse shows these or any other symptoms which you suspect may be caused internal pigeon fever abscesses. We have had two horses die from this condition in the last year.
If you notice suspicious swellings or abscesses and you suspect that your horse may have pigeon fever, call your local veterinarian. He or she will best be able to tell you whether or not your horse is infected through a careful physical exam and diagnostics such as blood work, ultrasound, and culture of abscess contents. Treatment is then tailored to each individual case but is largely supportive, consisting of NSAIDS for pain and hot-packing to encourage the abscesses to mature. In some instances, your veterinarian may prescribe antibiotics if deemed necessary. As with all infectious illnesses, strict cleanliness and confinement away from unaffected animals is imperative in preventing spread. Work with your veterinarian to figure out how this can best be addressed if you are dealing with a pigeon fever outbreak. There is no vaccine to prevent illness or infection, however, affected horses are rarely re-infected and it is thought that there is some natural immunity as a result.
The most effective way to combat pigeon fever, however, is through prevention. Conscientious fly-control and pasture management with frequent and regular removal of wastes can greatly reduce the likelihood of your horse becoming infected. The average stable fly will lay up to 800 eggs in its lifetime, the average 1000# horse can produce twice its own body weight in manure per month. If you consider that horse manure is a major food source and breeding ground for flies, you can just begin to imagine how many flies actually come into contact with your horse every single day! You can also begin to imagine how important it is to have a waste management plan in place. Removal of all manure and organic matter from confined areas such as stalls and small paddocks should be carried out at least once daily. Manure should not be allowed to collect in areas near where your horses are housed. Excess manure can be spread on pastures and fields to allow it to dry, thereby becoming less attractive as a food sources for flies. Other methods of fly control include fly traps and zappers for barns, and fly predators for smaller pastures. Sprays, roll-ons and lotions should also be used as often as directed to prevent flies from landing and biting. Masks and sheets are also good methods for keeping your horse fly-free!
The overall prognosis for affected horses is good and they will generally go on to heal quite well in spite of the alarming appearance of the infection. Adhering to the basic tenants of fly control outlined above however, can greatly reduce your horse’s risk, as well as bring you peace of mind!