Leptospirosis Getting an Early Start this Year

Erin Ryder
Researchers at the University of Kentucky's Livestock Disease Diagnostic Center have reported numerous early cases of leptospirosis, a bacterial disease that can cause a variety of equine problems, including abortion, a flu-like illness, and uveitis (moon blindness). Leptospirosis can spread from horses to humans.

Craig Carter, DVM PhD, a professor of epidemiology at the university, said the center has seen 10 cases of leptospirosis in Kentucky since October, compared to zero cases in the same timeframe last year.

With the upcoming Kentucky breeding and foaling season closing in, Carter said he believes there will be many more leptospirosis cases.

"It feels like we're maybe shifting a little earlier, maybe a couple of months, of when we see cases," Carter said. "Whether that's due to the rainfall or not, who knows, but it looks like a shift."

Carter said the Leptospira bacteria are particularly fond of wet weather, and are killed by drying or freezing, and as Kentucky transitions from a soggy fall into a wet winter, the conditions are just right for increased infection rates.

Carter said that the infected horses brought in to the diagnostic center so far have been mostly mid- to late-term abortions, with one weak neonate, and one older horse that died and was confirmed to be a carrier.

The Diagnostic Center has verified leptospirosis via a fluorescent antibody test performed on kidney and liver samples combined with pathology on the affected horses.

These tests considered in conjunction with the clinical signs of leptospirosis exhibited are diagnostic for the disease.

However, identifying living carrier horses isn't easy. Carter said the clinical signs can vary greatly, and some horses carrying the disease might not show signs at all while infecting other horses.

If a horse is suspected of having leptospirosis, a veterinarian can perform serologic and PCR tests on the horse's urine to see if it is possibly carrying the disease, but identifying such carriers within a herd is a challenge.

"(Testing is) kind of a shot in the dark because a lot of the time you'll have perfectly healthy animals walking around (that are carriers); you can't afford to just test everything to see if they're shedding," Carter noted.

Carter suggests that, if possible, horses should be kept away from rodents and other wildlife vectors, including deer and raccoons. Cows and dogs can also carry the bacteria.

There is no vaccine for leptospirosis for horses, but there are vaccines for dogs and cattle.

Leptospirosis is caused by spiral-shaped Leptospires. The bacteria can also cause azotemia (excess urine production), neonatal disease, and liver disease. The Leptospira bacteria are spread through urine and tend to set up shop in the horse's renal tubules.

Leptospira can cause what is known as equine recurrent uveitis which is an infection of the eye also known as moon blindness. An ophthalmologic exam should be done by a veterinarian when leptospirosis is suspected.

"(Leptospirosis is) always something you think about when we see (abortion) numbers like this at the diagnostic lab... our lab only sees the tip of the iceberg, so it makes us concerned," Carter said.

He added that the diagnostic laboratory is in the process of putting out informational bulletins on the disease and is building an automated statewide animal health surveillance system for the early detection of disease clusters in the horse.

"Timely alerting of practicing veterinarians regarding outbreaks of disease is crucial to bringing a fitting medical response to the farms in the area," Carter noted.