Prevalence of equine ulcerative keratomycosis in Colorado and association of environmental factors: A retrospective and descriptive study (2002–2017)

Abstract

SummaryEquine ulcerative keratomycosis is relatively commonly presented to teaching hospitals in North America, with a prevalence from 24 to 86%. Horses in Colorado may have lower risk due to the dry mountain climate, but data are lacking. This study aimed to determine the prevalence of ulcerative keratomycosis amongst horses with ulcerative keratitis presented to Colorado State University Veterinary Teaching Hospital (CSU‐VTH) ophthalmology service and to evaluate environmental factors (season, temperature, humidity, wind speed and elevation) associated with ulcerative keratomycosis in Colorado. A database search identified horses with ulcerative keratitis presented to the ophthalmology service at CSU‐VTH from January 2002 to August 2017. Sixty‐one horses met the inclusion criteria of a corneal cytology and/or culture or histopathology at the time of diagnosis; cases lacking that were excluded. Environmental factors at the boarding sites, including season, temperature, humidity, wind speed and elevation and clinical outcomes for fungal cases, were recorded. Prevalence of fungal infection amongst equine ulcerative keratitis was 16.4% (10/61), suggesting that CSU‐VTH has considerably fewer ulcerative keratomycosis cases than other veterinary teaching hospitals in North America. Spring (50%, 5/10) and fall (40%, 4/10) had the highest prevalence of fungal ulcerative keratitis in Colorado. Only one case was reported in summer (10%, 1/10); no horses were positive (0%, 0/10) in winter. Only wind speed seemed to influence the development of ulcerative keratomycosis with higher wind speeds associated with greater rates of fungal involvement (P = 0.047). Other environmental factors did not show a detectable association (all P‐values >0.05). Outcomes were variable. It was concluded that horses from the area of CSU‐VTH appear to be at lower risk for ulcerative keratomycosis than from the areas around other North American veterinary teaching hospitals that have reported data. Most horses with keratomycosis in this area present in the spring and fall.