The amount and type of Rhodococcus equi in a farm’s soil is not an indicator of an increased likelihood of having foal pneumonia cases caused by this bug, reported researchers from Texas A&M University. Additionally, farms with a greater density of mares and foals on the property are more likely to have cases of foal pneumonia attributable to Rhodococcus equi than farms with fewer horses.

Rhodococcus equi (R. equi) is a bacterium that causes pneumonia in foals. In North America the pathogenic (disease-causing) form of R. equi is endemic on some farms and approximately 10-20% of foals on endemic farms develop clinical signs of pneumonia.

“To date, it is unclear why some foals on some farms develop pneumonia caused by the pathogenic strain of R. equi and not others,” explained Noah Cohen, VMD, MPH, PhD, Dipl. ACVIM, of Texas A&M’s Department of Large Animal Clinical Science, and lead author on this study. “We performed this study to determine if an association existed between soil concentrations of the pathogenic strain of R. equi and the number of foals with R. equi-associated pneumonia.”

Investigators obtained soil samples from 37 farms in Central Kentucky and measured the concentrations of both total R. equi and the disease-causing form of R. equi in January, March, and July of 2006.

Sixteen of the 37 farms had foals affected with R. equi-associated pneumonia in 2006, while the remaining 21 farms were free of the disease.

Soil concentrations of total or pathogenic R. equi did not differ between the farms during the study per