Dr. Sharon Spier is a brilliant member of the faculty at the U.C. Davis School of Veterinary Medicine in California. I recently attended one of her lectures at a veterinary conference. The subject was Pigeon Fever, a rapidly spreading disease of horses caused a bacteria, Corynebacterium pseudotuberculosis.
I never heard of this disease when I was in veterinary school in Colorado, nor when I practiced in Arizona.
However, after I moved to Southern California in 1957 I saw many hundreds of cases. Known as “Dryland Distemper” a majority of cases involved abscessation in the pectoral muscles of the chest. The huge swellings led to the term “Pigeon Fever”.
Nearly all of these cases survived, but in some cases the abscesses developed elsewhere as in the belly wall, the sheath of males, or the udder of mares. Still, most cases survived, with or without treatment. However, sometimes the abscesses were internal, as in the abdomen. If such an abscess ruptured, the patient usually died.
Back then, how the disease was spread and why it was so regional (mostly in Southern California, but some in the North) was a mystery.
I was aware of several factors:
1. Those ranches and stables that used fly repellants on their horses rarely got the disease. Most of the cases I saw were at places that did not regularly use repellants on the horses even though many of them used insecticides on the premises.
Similarly, once Fly Predators (Spalding Laboratories) became available, the users very rarely experienced the disease. So, for example, because I have always used repellants on my equines, and Fly Predators on the premises since 1979, I have never had a case of the disease in my stock.
This led me to believe that the bacteria were spread by biting flies, now a proven fact. House Flies, Stable Flies and Horn Flies have been incriminated.
2. I often saw cases in the same horse year after year. This suggested a poor immune response and it explains why, after half a century, a simple effective vaccine is not yet available. Research continues.
3. The disease has spread slowly, but progressively all over the U.S.A. and elsewhere. It is more common in warmer climates (probably because of a longer fly season) but now is seen in all climate zones.
Although not a highly fatal disease, it is a nasty, painful, and debilitating problem. For now the best preventative seems to be fly control, including the regular use of repellants on the horses, plus proper use of Fly Predators. On small properties, like mine, this necessitates convincing neighbors to use Fly Predators. I was able to do this. Many horse properties are small enough so that even if Fly Predators are used, the flies from neighboring properties negate the effectiveness of the program.
I have often thought that subdivisions zoned for horses and horse clubs would do well to adopt a Fly Predator program as a communal effort.
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