Scientists have characterized the bacterial culprit behind nocardioform placentitis, a reproductive disease of Thoroughbred racehorses that's caused hundreds of cases of weakened or stillborn foals on farms in Kentucky's Bluegrass region since 1986.
Genetic analysis of the bacterium led scientists to conclude it is a new species in the genus Crossiella, named C equi. The accomplishment narrows down the list of potential suspects that veterinary scientists have to check when diagnosing the disease in horses or researching the nature of the disease for clues on how it might be prevented using antimicrobials, new animal husbandry practices, or other measures.
There were 144 U.S. cases of nocardioform placentitis reported in 1999 and 48 in 2000, all on central Kentucky farms. The disease is characterized by lesions that compete for nutrients flowing across the placenta to the developing fetus from the mare's uterus. This can result in an aborted fetus during late gestation, or a weak or stillborn foal.
In 1999, microbiologist J. Michael Donahue, PhD, and colleagues at the University of Kentucky's Livestock Disease Diagnostic Center in Lexington noticed that portions of C equi's genetic code matched those of other bacterial strains in a collection maintained by microbiologist David P. Labeda, PhD, of the National Center for Agricultural Utilization Research, Peoria, Ill. Dr. Labeda oversees the Actinobacterial Germplasm Collection.
Through analysis of the genetic sequences and comparison with another closely related species, C cryophila, the scientists determined that the isolates from the horses were indeed of the genus Crossiella—albeit a new species, equi—and one of the few actinomycetes known to cause animal disease.
But there's much still to learn about C equi, Dr. Labeda notes. One critical piece of intelligence in the fight against nocardioform placentitis will come from studies revealing where and how the bacterium lives in the environment, and at what life stage.
"I've collected some environmental samples. ...We're still trying to evaluate the best way to isolate the organism," Dr. Labeda said. "Right now we have no idea how it's getting into horses; it's a sporadic infection."