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In the News: Tails of Marin

By Marina Eisenzimmer

Pigeon Fever in Marin County a problem for horses

Many barns in Marin County have confirmed cases of Pigeon Fever. According to a number of local veterinarians, at least 200-300 horses have recently been affected. Surprisingly, the hotter and drier the location, the more likelihood there is for outbreaks. Novato, in particular, is a hotbed for Pigeon Fever. Dr. Myron Hinrichs of Sonoma-Marin Veterinary Services reports that, in his 38 years of veterinary practice, this year is the worst. His clinic has treated more than 100 horses in Marin County alone; luckily, few have died.

Horses in their mid-20s are more vulnerable to Pigeon Fever because they cannot mount an immune response and fight off the infection. And some horses have had internal abscesses that are more difficult to treat. The disease is not spread by horses touching each other – the culprit is flies. Flies find the small cuts and wounds on a horse and cause infections and abscesses. Fly control is crucial for prevention.

According to Bay Area veterinarian Dr. Douglas Novick, the bacteria involved are called Corynebacteria Pseudo tuberculosis. There are two reasons that it goes by the name Pigeon Fever. The first reason is that only five people in the United States can pronounce Corynebacteria Pseudo tuberculosis. The second reason stems from the behavior of the disease. Pigeon Fever tends to cause abscesses in the chest area of the horse. As the abscess develops the chest swells much like the prominent chest of a pigeon. Thus the name.

However, the chest is not the only place abscesses can form. It can occur in the girth area, and other parts of the horse’s body. The disease starts with a firm diffuse swelling over the affected region. The hard swelling enlarges and then softens like a water balloon as the abscess comes to a head. At this point the abscess either pops by itself or is lanced by your veterinarian. It is not uncommon for affected horses to have a mild temperature of 102 to 103 degrees.

Veterinary treatment usually consists of hot packing the swelling until an abscess has formed and is ready to lance. Once the abscess is lanced the open wound is cleaned daily and the horse is put on antibiotics for an extended period of time. The problem with Pigeon Fever is that it can cause multiple abscesses in a given horse. About one in five cases will have another abscess once the antibiotics are stopped. In very rare cases a horse can even get an internal abscess which can result in peritonitis when it breaks open. At the first signs of swelling it is tempting to put your horse on antibiotics right away. However, doing so may increase the risk of internal abscesses forming. It is for this reason that most cases require waiting until the abscess has formed and been lanced before instituting antibiotic treatment.

There is no vaccination for Pigeon Fever. It does follow a pattern of having one or two years when many horses in an area will get the disease. Then several years will follow without any cases being seen. This implies that horses in an area will develop a resistance on their own which gradually diminishes with time. Because it is spread by flies, on a given ranch if one horse becomes affected, it is likely that a small number of additional cases will be seen. However, unlike strangles, it is not likely that you will see more than a small percentage of horses on any one farm come down with the disease.

Pigeon Fever is not fatal but requires much care. Contact your Vet if you suspect Pigeon Fever. 

Marina Eisenzimmer is Vice President of the Marin Horse Council, which works with the Marin Humane Society to promote responsible horse care. The Marin Humane Society contributes Tails of Marin articles. Write to Tails of Marin, 171 Bel Marin Keys Blvd. Novato, CA 94949. For more information, call 883-4621 or visit MarinHumaneSociety.org.

Tails of Marin appears every Saturday in the Home & Garden section of the Marin Independent Journal