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“Doc, My Horse Has A Big Swollen Chest...”

By Wade Tenney, DVM

Published in Bay Area Equestrian Network February 2008

It seems that mother nature always likes to keep horse owner’s on their toes. She’s constantly bringing a different equine disease to the forefront, forever making horse owners keep vigilant watch over their equine friends. A few years ago it was West Nile Disease, last year it was Equine Herpes Virus. Now the current “hot topic” is Pigeon Fever, which has recently made a resurgence in California. Pigeon Fever, also known as Dryland Distemper, is a bacterial disease caused by Corynebacterium pseudotuberculosis. The disease is endemic in California, but has now also made its way through most of the western states. The disease is most commonly seen in the fall, but don’t let your guard down, as it can occur at any time during the year. The organism is transmitted by flies and enters the horse’s body through wounds, broken skin or mucous membranes. The organism can survive as a surface contaminant on stalls halters, feed troughs, hay etc. for up to 55 days, but lives in the soil for a very long time. The early signs of Pigeon Fever are vague and include lameness or reluctance to move, fever, inappetance and depression. Infection typically results in abscesses that eventually drain a thick, white/yellow pus material.

Abscesses most commonly appear in the chest region, giving the horse the classic pigeon-like appearance. Abscesses are also commonly seen on the underside of the horse’s abdomen, in the groin area and occasionally along the back. The disease is not limited to external body parts, but can also affect internal organs. We recently had two horses at our clinic that had external pigeon fever abscesses but also developed focal abscesses within the lung. This is important to remember as the development of internal abscesses may occur months to years after the external abscesses are resolved. So if your horse then has medical problems down the road, don’t forget to tell your veterinarian that your horse had pigeon fever at one time as this information may help in the workup.

The diagnosis of the disease is generally very easy. In many cases where the signs and timing are right, it may be an obvious diagnosis of Pigeon Fever. In other cases, your veterinarian may need to collect a sample to culture in the laboratory.

If your horse has developed a pigeon fever abscess, the area should be treated with hot packs or poultices to bring the abscess to the surface so it can drain. Some infections may be very deep and have a large painful swelling for weeks or months before it comes to the surface. Once the abscess develops a soft, fluctuant center it is ready to be lanced and drained by your veterinarian. The abscess should then be flushed with saline and Betadine. If the abscess and drainage site are particularly large, the area may be packed with antiseptic soaked gauze. Non-steroidal anti-inflammatories such as Bute may be helpful in reducing the inflammation and making your horse more comfortable. There is still considerable debate about the use of antibiotics to treat Pigeon Fever. Some people believe that if antibiotic therapy is initiated too early, you may increase the likelihood of developing internal abscesses. The general policy at our clinic is to allow the abscess to come the surface and drain without the use of antibiotics. Antibiotics are only started if the horse is clinically ill, is known to have internal abscesses or has been chronically affected for a long time. When treating horses with internal abscesses, antibiotic therapy generally ensues for several months!

This disease is contagious and so reasonable diligence and care should be taken when treating an affected horse. The horse should be somewhat isolated and not have direct contact with other horses. Buckets should be used to collect pus from a draining abscess to prevent unnecessary contamination of the soil where the organism likes to live. Remember that the organism can live on the surface of stalls, tack and cleaning supplies for up to 55 days, so these items should be disinfected to minimize spread of the disease. Fly control is also an important factor in containing the disease. Pigeon Fever cannot be spread to humans; however it can be carried to another horse on our hands and feet, so we need to be careful especially when dealing with an actively draining abscess.

So for those of you who may notice an abnormal swelling on your horse, consider having your veterinarian examine the horse for Pigeon fever. For those of you currently dealing with an abscess that may be taking a long time to drain – hang in there! The good news is that most horses go on to complete recovery. Hopefully we will someday develop a vaccine for pigeon fever and lay this disease to rest!!!


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