R. Equi and Extrapulmonary Disorders, AAEP 2008

Rhodococcus equi bronchopneumonia is a prevalent cause of disease in foals, said M. Keith Chaffin, DVM, MS, Dipl. ACVIM, a professor of medicine at Texas A&M University's vet school, at the 2008 American Association of Equine Practitioners convention, which was held Dec. 6-10 in San Diego, Calif. (The lead author of the paper was Sarah M. Reuss, VMD, of Texas A&M, but she was unable to attend and Chaffin made the presentation.)

Chaffin said the problem with R. equi goes deeper than that because the bacterium is also associated with extrapulmonary disorders (EPDs).

These extrapulmonary disorders, Chaffin said, often are difficult to recognize clinically, but they can affect the outcome of a sick foal. A study was launched at Texas A&M to describe the frequency, types, and outcome of extrapulmonary disorders and to identify risk factors.

After reviewing medical records of foals diagnosed with R. equi infections at Texas A&M between 1987 and 2007, it was decided that 150 foals met the criteria for inclusion in the study.

Of that number, 74% had at least one of 39 different extrapulmonary disorders. Listed as the most commonly identified extrapulmonary disorders were diarrhea, immune-mediated polysynovitis (similar to rheumatoid arthritis in humans), ulcerative enterotyphlocolitis (small erosions and abscesses in the wall of the small or large intestines), intra-abdominal abscessation, abdominal lymphadenitis (inflammation in one or more lymph nodes), uveitis (moon blindness), and pyogranulomatous hepatitis (microscopic abscesses in the liver).

The researchers had this to report in conclusion: "Risk factors significantly associated with the presence of extrapulmonary disorders included referral status, duration of clinical signs before admission, increased heart rate, leukocytosis (undue increase in the number of white blood cells), neutrophilia (more than the normal number of neutrophils, which are specialized white blood cells capable of engulfing and destroying bacteria and other disease agents), and increased blood urea nitrogen concentration. Survival rate was significantly higher among foals without EPDs (82%) than among foals with EPDs (43%), but many EPDs were only recognized post-mortem.

"There was a wide variety of EPDs, and some of these seemed to have a negative impact on outcome," the researchers noted. "All foals with R. equi, especially those with profound leukocytosis and/or azotemia (an excess of urea or other nitrogenous bodies in the blood), warrant a thorough diagnostic assessment for EPDs."

About the Author

Les Sellnow

Les Sellnow is a free-lance writer based near Riverton, Wyo. He specializes in articles on equine research, and operates a ranch where he raises horses and livestock. He has authored several fiction and non-fiction books, including Understanding Equine Lameness and Understanding The Young Horse, published by Eclipse Press and available at www.exclusivelyequine.com or by calling 800/582-5604.

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