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Temporal clinical exacerbation of summer pasture-associated recurrent airway obstruction and relationship with climate and aeroallergens in horses

Lais R. R. Costa MV, MS, PhD1, Jill R. Johnson DVM, MS2, Matthew E. Baur PhD3, and Ralph E. Beadle DVM, PhD4
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  • 1 Equine Health Studies Program, Departments of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803-8410; Pathobiological Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803-8410.
  • | 2 Equine Health Studies Program, Departments of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803-8410.
  • | 3 Department of Entomology, Agriculture Center, Louisiana State University, Baton Rouge, LA 70803-8410.
  • | 4 Equine Health Studies Program, Departments of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803-8410.

Abstract

Objective—To describe the seasonal pattern of clinical exacerbation of summer pasture-associated recurrent airway obstruction (SPA-RAO) in relation to climate and aeroallergens in horses.

Animals—19 horses with SPA-RAO and 10 nonaffected horses.

Procedures—Daily examinations were performed on all horses while they were kept on pasture for 3 years. Onset and progression of clinical exacerbation based on a clinical score of respiratory effort were evaluated in relation to changes in maximum temperature, minimum temperature, mean temperature, maximum dew-point temperature, minimum dew-point temperature, and delta dew-point temperature. Seasonal pattern of clinical exacerbation was evaluated in relation to aeroallergen counts (20 types of fungal spores and 28 types of pollen).

Results—Seasonal pattern of clinical exacerbation of SPA-RAO was associated with increases in temperature (heat) and dew-point temperature (humidity), counts of fungal spores, and counts of grass pollen grains. Seasonal pattern of clinical exacerbation paralleled and was associated with increases in counts of specific types of fungal spores, particularly Basidiospore, Nigrospora, and Curvularia spp.

Conclusions and Clinical Relevance—Although a causal relationship could not be determined, the seasonal pattern of clinical exacerbation of SPA-RAO was associated with hot and humid conditions and high environmental counts for fungal spores and grass pollen grains. It is not known yet whether these are aeroallergens that cause clinical exacerbation of the disease.

Abstract

Objective—To describe the seasonal pattern of clinical exacerbation of summer pasture-associated recurrent airway obstruction (SPA-RAO) in relation to climate and aeroallergens in horses.

Animals—19 horses with SPA-RAO and 10 nonaffected horses.

Procedures—Daily examinations were performed on all horses while they were kept on pasture for 3 years. Onset and progression of clinical exacerbation based on a clinical score of respiratory effort were evaluated in relation to changes in maximum temperature, minimum temperature, mean temperature, maximum dew-point temperature, minimum dew-point temperature, and delta dew-point temperature. Seasonal pattern of clinical exacerbation was evaluated in relation to aeroallergen counts (20 types of fungal spores and 28 types of pollen).

Results—Seasonal pattern of clinical exacerbation of SPA-RAO was associated with increases in temperature (heat) and dew-point temperature (humidity), counts of fungal spores, and counts of grass pollen grains. Seasonal pattern of clinical exacerbation paralleled and was associated with increases in counts of specific types of fungal spores, particularly Basidiospore, Nigrospora, and Curvularia spp.

Conclusions and Clinical Relevance—Although a causal relationship could not be determined, the seasonal pattern of clinical exacerbation of SPA-RAO was associated with hot and humid conditions and high environmental counts for fungal spores and grass pollen grains. It is not known yet whether these are aeroallergens that cause clinical exacerbation of the disease.

Contributor Notes

Dr. Costa's present address is the Department of Clinical Sciences, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA 01536.

This report represents a portion of a dissertation submitted by the first author to the graduate school, Louisiana State University as partial fulfillment of the requirements for the PhD degree.

Supported by a grant from the Louisiana State University Equine Health Studies Program.

The authors thank Kevin Robbins, Jay Grimes, Dr. O. Huh, Susan Sturm, Dr. Powlin Manuel, Frank Garza, Kimberly Cousey, Jesse McClure, Dr. Paul Hollier, and Dr. Thomas Seahorn for their assistance.

Address correspondence to Dr. Costa.