Scientist Sleuths in Pursuit of Racehorse Disease

By Jan Suszkiw
December 13, 2001

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 veterinary scientists have to check when diagnosing horses or researching the nature of the disease for clues on how it might be prevented using antibiotics, new animal husbandry practices, or other measures.

There were 144 U.S. cases of nocardioform placentitis 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, J. Michael Donahue and colleagues at the University of Kentucky's Livestock Disease Diagnostic Center in Lexington noticed portions of C. equi's genetic code matched those of other bacterial strains in a collection maintained by microbiologist David Labeda at the Agricultural Research Service.

Labeda oversees the Actinobacterial Germplasm Collection at ARS' National Center for Agricultural Utilization Research, Peoria, Ill. Through careful analysis of the genetic sequences, and comparison with another closely-related species, C. cryophila, the scientists determined that the equine isolates were indeed a member of the genus Crossiella—albeit a new species (C. equi)—and one of the few actinomycetes known to cause animal disease.

But there's much still to learn about C. equi, notes Labeda. 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. Also important is determining how the bacterium finds its way into the mare's uterus and causes infection. A more detailed story appears in the December issue of Agricultural Research magazine.

ARS is the U.S. Department of Agriculture's chief scientific agency. In Peoria, Labeda works in the ARS center's Microbial Genomics and Bioprocessing Research Unit.