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Association of perinatal exposure to airborne Rhodococcus equi with risk of pneumonia caused by R equi in foals

Noah D. CohenEquine Infectious Disease Laboratory, Department of Large Animal Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX 77843.

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M. Keith ChaffinEquine Infectious Disease Laboratory, Department of Large Animal Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX 77843.

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Kyle R. KuskieEquine Infectious Disease Laboratory, Department of Large Animal Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX 77843.

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Melissa K. Syndergaard6666 Ranch, 1102 Dash For Cash Rd, Guthrie, TX 79236.

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Glenn P. Blodgett6666 Ranch, 1102 Dash For Cash Rd, Guthrie, TX 79236.

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Shinji TakaiDepartment of Animal Hygiene, School of Veterinary Medicine and Animal Sciences, Kitasoto University, Towada, Aomori 034-8628, Japan.

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Abstract

Objective—To determine whether the concentrations of airborne virulent Rhodococcus equi in stalls housing foals during the first 2 weeks after birth are associated with subsequent development of R equi pneumonia in those foals.

Sample—Air samples collected from foaling stalls and holding pens in which foals were housed during the first 2 weeks after birth.

Procedures—At a breeding farm in Texas, air samples (500 L each) were collected (January through May 2011) from stalls and pens in which 121 foals were housed on day 1 and on days 4, 7, and 14 after birth. For each sample, the concentration of airborne virulent R equi was determined with an immunoblot technique. The association between development of pneumonia and airborne R equi concentration was evaluated via random-effects Poisson regression analysis.

Results—Some air samples were not available for analysis. Of the 471 air samples collected from stalls that housed 121 foals, 90 (19%) contained virulent R equi. Twenty-four of 121 (20%) foals developed R equi pneumonia. Concentrations of virulent R equi in air samples from stalls housing foals that developed R equi pneumonia were significantly higher than those in samples from stalls housing foals that did not develop pneumonia. Accounting for disease effects, air sample concentrations of virulent R equi did not differ significantly by day after birth or by month of birth.

Conclusions and Clinical Relevance—Exposure of foals to airborne virulent R equi during the first 2 weeks after birth was significantly (and likely causally) associated with development of R equi pneumonia.

Abstract

Objective—To determine whether the concentrations of airborne virulent Rhodococcus equi in stalls housing foals during the first 2 weeks after birth are associated with subsequent development of R equi pneumonia in those foals.

Sample—Air samples collected from foaling stalls and holding pens in which foals were housed during the first 2 weeks after birth.

Procedures—At a breeding farm in Texas, air samples (500 L each) were collected (January through May 2011) from stalls and pens in which 121 foals were housed on day 1 and on days 4, 7, and 14 after birth. For each sample, the concentration of airborne virulent R equi was determined with an immunoblot technique. The association between development of pneumonia and airborne R equi concentration was evaluated via random-effects Poisson regression analysis.

Results—Some air samples were not available for analysis. Of the 471 air samples collected from stalls that housed 121 foals, 90 (19%) contained virulent R equi. Twenty-four of 121 (20%) foals developed R equi pneumonia. Concentrations of virulent R equi in air samples from stalls housing foals that developed R equi pneumonia were significantly higher than those in samples from stalls housing foals that did not develop pneumonia. Accounting for disease effects, air sample concentrations of virulent R equi did not differ significantly by day after birth or by month of birth.

Conclusions and Clinical Relevance—Exposure of foals to airborne virulent R equi during the first 2 weeks after birth was significantly (and likely causally) associated with development of R equi pneumonia.

Contributor Notes

Supported by the American Quarter Horse Foundation and the Link Equine Research Endowment, Texas A&M University.

The air sampler used for this project was purchased with a grant from the Grayson-Jockey Club Research Foundation.

The authors thank Stephanie Buntain, Stephanie Standridge, Grant Wicks, and Kyle Wicks for technical assistance.

Address correspondence to Dr. Cohen (ncohen@cvm.tamu.edu).