The Fecal Bacterial Microbiota in Horses with Equine Recurrent Uveitis

Abstract

The objective of this study was to describe and compare the fecal bacterial microbiota of horses with equine recurrent uveitis (ERU) and healthy horses using next-generation sequencing techniques. Fecal samples were collected from 15 client-owned horses previously diagnosed with ERU on complete ophthalmic examination. For each fecal sample obtained from a horse with ERU, a sample was collected from an environmentally matched healthy control with no evidence of ocular disease. The Illumina MiSeq sequencer was used for high-throughput sequencing of the V4 region of the 16S rRNA gene. The relative abundance of predominant taxa, and alpha and beta diversity indices were calculated and compared between groups. The phyla Firmicutes, Bacteroidetes, Verrucomicrobia, and Proteobacteria predominated in both ERU and control horses, accounting for greater than 60% of sequences. Based on linear discriminant analysis effect size (LEfSe), no taxa were found to be enriched in either group. No significant differences were observed in alpha and beta diversity indices between groups (p > 0.05 for all tests). Equine recurrent uveitis is not associated with alteration of the gastrointestinal bacterial microbiota when compared with healthy controls.

A review of investigated risk factors for developing equine recurrent uveitis

“…[102][103][104] A recent investigation comparing microbiota in ERU affected and unaffected horses did not identify a significant difference in gut microbe diversity or composition, suggesting that dysbiosis may not be a risk factor for ERU. 105 However, the study did not distinguish between the different forms of ERU among the affected horses, and further investigations of ERU and gut microbiota should evaluate affected horses with a specific classification of ERU (posterior, classic, or insidious) or use a breed-specific analysis. Additionally, a possible role of gut microbiota in distinguishing between active and quiescent phases of the recurrent forms of ERU (posterior and classic) remains to be investigated.…”

“…In humans, investigations into diet, obesity, activity level, and microbiome composition have not identified any other prominent environmental characteristics affecting uveitis onset, although some results suggest that these factors may have a role in disease progression 102–104 . A recent investigation comparing microbiota in ERU affected and unaffected horses did not identify a significant difference in gut microbe diversity or composition, suggesting that dysbiosis may not be a risk factor for ERU 105 . However, the study did not distinguish between the different forms of ERU among the affected horses, and further investigations of ERU and gut microbiota should evaluate affected horses with a specific classification of ERU (posterior, classic, or insidious) or use a breed‐specific analysis.…”

Alterations of the bacterial ocular surface microbiome are found in both eyes of horses with unilateral ulcerative keratitis

“…It is possible that intrinsic factors, such as sex, age or genetic deficiencies, as well as extrinsic factors, such as environment (climate, season, weather, housing) may play a role in the pathogenesis of disease [14,45,46], although a recent study investigating the microbiome and mycobiome in healthy horses did not identify age, breed or sex as risk factors [17]. Gut dysbiosis has been associated with immune-mediated diseases in humans [7,42]. Some authors have proposed that specific gut bacteria may contribute to modulation of T-regulatory cells, resulting in an increased susceptibility to immune-mediated processes [7].…”

“…Gut dysbiosis has been associated with immune-mediated diseases in humans [7,42]. Some authors have proposed that specific gut bacteria may contribute to modulation of T-regulatory cells, resulting in an increased susceptibility to immune-mediated processes [7]. The investigation of gut microbiota composition in human patients with acute anterior uveitis (AAU) had a unique fecal metabolic phenotype compared with controls [47].…”

“…This methodology can identify microbes that would previously remain undetected [2]. In recent years, 16S rRNA gene sequencing has become a viable option for identifying a diverse population of ocular microorganisms within veterinary species, such as cats [3,4], horses [5][6][7], and dogs [8][9][10][11]. This modality within veterinary medicine has similarly proven advantageous in revealing bacterial microorganisms that do not grow well in laboratory conditions and would otherwise go unidentified with culture-based methods.…”