LEPTOSPIROSIS
up infected insects, or they may drink contaminated water.
• Take special precautions when insect populations are at their highest. Finally, be aware of when populations of local aquatic insects are likely to peak. In some areas, insects that carry PHF may hatch and emerge by the thousands to mate and die within hours. Your local agricultural extension office may be able to help warn you of impending hatches. At those times, you’ll want to take extra precautions to protect your horse, perhaps by keeping him inside with the lights off. A bacterial infection caused by Leptospira spp. spirochetes , leptospirosis is found in many species of animals worldwide. The spirochetes are shed in the urine of infected animals, and horses may pick up the infection through physical contact with co soil. “W the mo skin ca leptosp membr h h wa by ar fro ing into the eyes.”
Leptospira spp. spirochetes are subdivided into multiple species with hundreds of serovars, which are variants within a species that produce different surface antigens. Six different serovars affect horses in North America, but the one that causes the most equine disease is Leptospira interrogans serovar Pomona, usually shortened to L. pomona.
“Certain types are host-adapted to a specific species of animal. They are ‘normal’ in that species; those animals can carry and shed it, but it doesn’t cause illness. If that type gets into another species, it does cause infection and illness,” says Grenager. “[ L. pomona] can be carried in other animals, particularly skunks. The skunk is one of the most common maintenance hosts for L. pomona in the horse’s environment, and the horse gets it by accident.”
But skunks aren’t the only potential source of L. pomona, which can also be carried by pigs, cattle, dogs, rodents and other domestic and wild species. “The horse is always an accidental infection,” says Grenager. “Skunks, rodents and other wild animals urinating in feed or water or in a barn stall can spread lepto to horses. Infected cattle or other farm animals can spread it as well, in a shared environment.”
When a horse is first infected with L. pomona, the bacteria multiply and circulate in the bloodstream. As he develops antibodies, he may have a fever, go off his feed and be depressed and lethargic. These signs can be subtle and easy to miss. After the initial infection, most horses never develop further signs of illness. However, if the horse’s immune system doesn’t control the bacteria, they may colonize specific organs---usually the eyes, the kidneys or the uterus--producing signs weeks or months after the exposure.
In the eyes, leptospirosis causes equine recurrent uveitis (ERU), also called “moon blindness,” an autoimmune disease that causes repeated inflammation of the uveal tract, the middle layer of the wall of the eyeball. “We often see recurrent uveitis and immune-mediated keratitis---eye