Septic Endophthalmitis Following Suprachoroidal Cyclosporine Implant Placement in Two Horses With Equine Recurrent Uveitis

To describe the most common ocular abnormalities in the Icelandic horse with focus on equine recurrent uveitis (ERU) and association between ocular abnormalities and summer eczema and coat colors. A descriptive cross-sectional study. A complete physical and ophthalmic examination as well as measurement of serum titers for Leptospira serovariants was performed on Icelandic horses from Denmark (DK) and the United States (USA). One hundred and twelve Icelandic horses living in DK and 26 Icelandic horses living in the United States were included in this study (total of 138horses, 274 eyes). The three most common ocular abnormalities were follicular conjunctivitis (55.8%, 153/274 eyes), cataracts (27.4%, 75/274 eyes), and multifocal chorioretinopathy ("bullet holes"; 19%, 52/274 eyes). The prevalence for ERU among Icelandic horses aged "eight years and older" was 8% (6/75horses). The "insidious ERU" type was found in 83% of the ERU cohort (5/6horses), while "classic ERU" was found in 17% (1/6horses). A correlation between ERU and cataracts was found in the population (p<.01). Leptospiral serology results were not associated with ERU in either DK or US-Icelandic horses (p=1.00, p=1.00, respectively). ERU was not associated with summer eczema (p=.49), and no coat colors were associated with the ocular abnormalities found in the Icelandic horse (all p-values>.05). Follicular conjunctivitis, cataracts, and multifocal chorioretinopathy were the three most common ocular abnormalities findings. Icelandic horses who were 8years or older had an 8% prevalence for ERU. Summer eczema and coat color were not associated with evidence of ERU or other ocular abnormalities.

Simple SummaryEquine recurrent uveitis (ERU) is an immune-mediated disease characterized by recurrent episodes of intraocular inflammation. Despite being a major cause of blindness in horses worldwide, the exact pathogenesis of ERU remains unknown. Recently, changes in the normal balance of the gastrointestinal tract bacteria (also known as dysbiosis) have been described in several immune-mediated diseases in humans, including uveitis. As such, the objective of this study was to compare the fecal bacterial community (the fecal microbiota) of horses with ERU with that of healthy horses living on the same farms. Study results revealed no significant alterations in the fecal microbiota between horses with ERU and healthy horses housed in the same environment. In order to better determine if there is an association between dysbiosis and ERU, future investigations are warranted to more specifically compare the fecal microbiota of horses that are having active flare-ups of ERU with that of horses in a quiescent period of the disease and with healthy horses.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.

To determine the role of intraocular bacteria in the pathogenesis of equine recurrent uveitis (ERU) in horses from the southeastern United States by evaluating affected eyes of horses with ERU for bacterial DNA and intraocular production of antibodies against Leptospira spp. Aqueous humor, vitreous humor, and serum samples of 24 clinically normal horses, 52 horses with ERU, and 17 horses with ocular inflammation not associated with ERU (ie, non-ERU inflammation). Ribosomal RNA quantitative PCR (real-time PCR) assay was used to detect bacterial DNA in aqueous humor and vitreous humor from clinically normal horses (n = 12) and horses with chronic (> 3-month) ERU (28). Aqueous humor and serum were also evaluated for anti-Leptospira antibody titers from clinically normal horses (n = 12), horses with non-ERU inflammation (17), and horses with confirmed chronic ERU (24). Bacterial DNA was not detected in aqueous humor or vitreous humor of horses with ERU or clinically normal horses. No significant difference was found in titers of anti-Leptospira antibodies in serum or aqueous humor among these 3 groups. Only 2 horses, 1 horse with ERU and 1 horse with non-ERU inflammation, had definitive intraocular production of antibodies against Leptospira organisms. In horses from the southeastern United States, Leptospira organisms may have helped initiate ERU in some, but the continued presence of the organisms did not play a direct role in the pathogenesis of this recurrent disease.

Cytokine and chemokine profiles of aqueous humor and serum in horses with uveitis measured using multiplex bead immunoassay analysis

Purpose: To evaluate the outcome of pars plana vitrectomy (PPV) in eyes with clinical signs of equine recurrent uveitis (ERU) testing positive or negative for intravitreal antibodies against various serovars of Leptospira interrogans. 47 eyes of horses with ERU in which intraoperative vitreous samples were tested by microagglutination (MAT) for various serovars of Leptospira interrogans between 2001 and 2009 were included in a retrospective study. The presence or absence of postoperative ERU was evaluated by repeated ocular examinations, as well as by interrogation of referring veterinarians and owners. The absence of recurrent episodes of active uveitis was considered a success irrespective of the visual performance of the operated eyes. 85% of eyes of horses with ERU had antibodies against L. interrogans in their vitreous. The most common serovar was L. grippothyphosa. The majority of horses testing positive for antibodies against L. interrogans (40/47; 82.5%) showed no further episodes of ERU, while 6/7 (85.7%) of horses testing negative continued to experience episodes of ERU. This difference is statistically significant. It appears that PPV is an effective treatment for Leptospira-associated ERU but not for eyes testing negative for antibodies against L. interrogans. Vitreal and aqueous humor samples of horses suffering from ERU should be tested by MAT before performing a PPV. Keywords: Equine recurrent uveitis, vitrectomy, Leptospira interrogans, antibodies, ophthalmology

Pars Plicata in Equine Recurrent Uveitis

Uveitis is a sight-threatening eye disease in equids known worldwide that leads to considerable pain and suffering. By far the most common type of uveitis in Germany and neighboring countries is classical equine recurrent uveitis (ERU), which is caused by chronic intraocular leptospiral infection and is the main cause of infectious uveitis in horses. Other infectious causes are extremely rare and are usually clinically distinguishable from ERU. ERU can be treated very effectively by vitreous cavity lavage (vitrectomy). For proper indications of this demanding surgery, it is necessary to differentiate ERU from other types of uveitis in which vitrectomy is not helpful. This can be conducted on the basis of anamnesis in combination with ophthalmologic findings and by aqueous humor examination. During vitrectomy, vitreous material is obtained. These vitreous samples have historically been used for numerous etiologic studies. In this way, a chronic intraocular leptospiral infection has been shown to be the cause of typical ERU and, among other findings, ERU has also been recognized as a biofilm infection, providing new insights into the pathogenesis of ERU and explaining some thus far unexplainable phenomena of ERU. ERU may not only have transmissible aspects to some types of uveitis in humans but may also serve as a model for a spontaneously occurring biofilm infection. Vitreous material obtained during therapeutically indicated vitrectomy can be used for further studies on in vivo biofilm formation, biofilm composition and possible therapeutic approaches.

Despite extensive clinical research, the etiology of equine recurrent uveitis (ERU) is still unknown. After an immunologic pathogenesis was established in recurrent uveitis in humans, a similar pathogenic mechanism was assumed to exist in ERU. To investigate whether immunopathologic mechanisms are involved in ERU, 20 eyes of 15 horses with ERU were examined immunohistochemically with a T cell marker, B cell marker, and anti-major histocompatibility complex (MHC) class II antibodies. Twenty-six eyes of 20 horses were used for investigation of MHC class II antigen expression in normal equine eyes. In 18 eyes of 14 horses, the number of T cells in the inflammatory cell population within the uvea was assessed. In 16/18 eyes (89%), the T lymphocyte fraction was > 70%. This cell population was distributed mostly in a diffuse manner throughout the uvea and also within the mantle zone of follicular lymphocytic aggregates. Foci of B lymphocytes could be found within the center of follicular aggregates in three eyes. The expression of MHC class II antigen on resident ocular cells was evaluated in 10 eyes of six horses with ERU. An increase of MHC class II antigen expression in the trabecular meshwork and on the nonpigmented ciliary epithelium was noted as was a deviant expression on proliferating Müller cells and retinal pigment epithelial cells. The predominance of T cells in the inflammatory infiltrates supports the central role of a cell-mediated immune response. Furthermore, the observation of a deviant MHC class II expression on resident ocular cells suggests that aberrant immune regulation may play a role in the pathogenesis of ERU.

Equine recurrent uveitis (ERU) is a spontaneous disease that is the most common cause of blindness in horses, affecting up to 15% of the horse population. Th17 cells are a major cell population driving the pathogenesis in several mouse models of autoimmune inflammation, including experimental autoimmune uveitis. The purpose of this study is to investigate the role a Th17 cell-mediated response plays in the pathogenesis of ERU. Banked, Davidson's-fixed equine globes histopathologically diagnosed with ERU (n = 7) were compared immunohistochemically with healthy control globes (n = 7). Immunohistochemical staining was performed using a pan-Leptospira antibody and antibodies against IL-6, IL-17, and IL-23. Additionally, immunostaining was performed for T-cell (CD3) and B-cell (CD79α) markers. Specificity of immunoreactivity was confirmed by western blot analysis. Immunohistochemical staining was positive for IL-6, IL-17, and IL-23 within the cytoplasm of nonpigmented ciliary epithelial cells and mononuclear inflammatory cells infiltrating the iris, and ciliary body of ERU horses (n = 7) but negative in controls (n = 7). ERU-affected eyes were CD3 positive (n = 7) and CD79α negative (n = 7). Staining for Leptospira was negative in all ERU and control globes. Strong immunoreactivity for IL-6, IL-17, and IL-23, in conjunction with the fact that T lymphocytes are the predominating inflammatory cells present in ERU, suggests that IL-17-secreting helper T-cells play a role in the pathogenesis of ERU. These findings suggest that horses with ERU may serve as a naturally occurring animal model for autoimmune uveitis.

Equine recurrent uveitis (ERU) is an autoimmune disease defined by inflammation of the uveal tract of the eye. The cause of ERU is thought to be complex, involving both genetic and environmental factors. The purpose of this study was to investigate potential genetic risk factors for ERU in the Icelandic horse. Fifty-six Icelandic horses (11 affected with ERU and 45 controls) living in Denmark and the USA, eight years or older, were included in the study. A case-control GWAS was performed using the GGP Equine 80K array on the Illumina Infinium HD Beadchip using 40 horses. A mixed linear model analysis identified a single SNP on ECA 11 (BIEC2_141650; NC_009154.3:g.3817009A>G) that reached genome-wide significance (p=1.79×10-7 ). This variant was within an intron of tissue inhibitor of metalloproteinase 2 (TIMP2), a gene previously implicated in ERU. Sanger sequencing identified a single coding variant in this gene; however it was a synonymous mutation (NC_009154.3:g.3858193C>T) and was not perfectly concordant with ERU phenotype (p=0.68). Further investigation of TIMP2 is warranted. Additional horses and markers are needed to identify other potential loci worthy of further investigation as contributors to ERU risk in Icelandic horses.

Role of Intraocular Leptospira Infections in the Pathogenesis of Equine Recurrent Uveitis in the Southern United States

To investigate the role of intraocular leptospiral infections in horses with Equine Recurrent Uveitis (ERU), ocular fluid samples were collected from donated and client-owned horses with a history and ocular findings consistent with chronic ERU. Additionally, eyes were harvested from horses with normal ophthalmic examinations as a control group. Blood samples were obtained for Leptospira serology using microscopic agglutination test (MAT). Aqueous and vitreous humor samples were aseptically obtained and submitted for aerobic culture and Leptospira culture, PCR and MAT. Twenty-one control horses (40 eyes) and 31 ERU horses (46 eyes) were available for study. Serology results were available for 48/52 horses: 16/21 control and 23/27 affected horses were positive for at least one serovar; Bratislava was the most common serovar for both groups. Bacillus sp. and Micrococcus sp. were cultured from one control eye; Streptococcus sp. (n=1) and Leptospira (n=6) from eyes with ERU. Leptospira isolated belonged to serogroup pomona (n=4) and grippotyphosa (n=2). PCR results were positive in 14/31 (45%) horses diagnosed with ERU; no control horses were positive by PCR (p=0.0001). MAT was positive for 17/24 of ERU horses (71%) and 1/21 (4.7%) of normal horses (p<0.0001). Horses with ERU had a high prevalence of Leptospira infection based on PCR and MAT results from intraocular fluids compared to controls. Leptospira infection should be considered as a cause of ERU in the southern United States. The diagnosis of these intraocular infections was not aided by serology and required specific, invasive sampling of ocular fluid.

Summary Background There is little information on the correlation between equine recurrent uveitis (ERU) and leptospiral infection status as it relates to ocular examination findings and testing recommendations. Objective To evaluate the role of leptospiral testing in horses with ERU by correlating results to signalment, clinical findings and visual outcome. Study design Retrospective case series. Methods Records of horses presenting for ERU at NC State University Veterinary Health Complex (NCSU‐VHC) between 2014 and 2019 were reviewed. Signalment, initial visual status, ocular examination findings, treatments and visual outcome were collected. Serum and aqueous humour (AH) leptospiral titres were assessed for six different leptospirosis serovars and polymerase chain reaction (PCR) testing. Goldmann‐Whitmer (C) values were calculated. Results Records of 63 horses and 78 eyes with ERU were evaluated. Horses with a positive aqueous humour PCR were significantly younger in age (mean 9.25 ± 1.14) than PCR negative horses (mean 13.3 ± 0.95) ( p = 0.01). A positive aqueous humour titre of any serotype was significantly correlated to blindness at presentation ( p = 0.04). A positive serum titre was significantly correlated to presence of ocular posterior segment disease ( p = 0.01). Positivity to L. bratislava in the serum correlated to posterior segment disease ( p = 0.04) and AH positivity correlated to blindness at presentation ( p = 0.002). Main limitations Limitations of this study include that it is a retrospective and information gathered relies on data included within medical records. Conclusions Positive leptospiral testing results were associated with younger horses and ocular posterior segment clinical disease. Horses with aqueous humour titres to any leptospiral serotype, especially L. bratislava serovar, were correlated to poor prognosis for vision.

To report concurrent clinical intraocular findings in horses with depigmented punctate chorioretinal foci and to document any correlation with equine recurrent uveitis (ERU). Records of 131 horses (241 eyes) examined at the University of Georgia Veterinary Teaching hospital from 2001 to 2010 were reviewed with either clinically normal fundi or depigmented punctate chorioretinal foci in the absence of other fundic pathology. Data collected included patient signalment, concurrent clinical ocular findings and follow-up information. Sex, presence of no other intraocular findings, presence of ERU, presence of cataracts, and presence of vitreal disease were compared between normal and foci groups using chi-squared analysis. Age and length of follow-up time were compared using a student's t-test. Ninety-one horses (167 eyes) with chorioretinal foci and forty horses (74 eyes) with clinically normal ocular fundi were examined. Fifty-eight (64%) horses with chorioretinal foci and 20 (50%) horses with clinically normal fundi had a normal intraocular examination. There was no significant difference in any of the criteria examined between groups. Horses with depigmented punctate chorioretinal foci, in the absence of other fundic pathology, are not more likely to have intraocular disease or ERU than horses with clinically normal ocular fundi. These findings suggest that depigmented punctate fundic foci in horses are not indicative of or associated with ERU.

Equine recurrent uveitis (ERU), a chronic, immune-mediated intraocular inflammatory disease, is a common cause of blindness in horses. The severity and recurrent nature of ERU makes it difficult to treat with current therapeutics leading to a poor visual prognosis. The suprachoroidal space (SCS), a potential space between the choroid and sclera surrounding the ocular posterior segment, offers a promising alternative site for drug application to the eye. Corticosteroid administration within this space is hypothesized to be safe and effective at controlling intraocular inflammation, especially in horses with poorly responsive ERU. Horses with active, poorly responsive ERU. A retrospective study was performed with 29 horses (36 total eyes) that received SCS injection of triamcinolone acetonide (TA) with ERU not well controlled with standard uveitis treatment. A standardized ocular inflammation score (OIS) was used to assess inflammation at the time of injection and at follow-ups. Standardized OIS revealed a significant decrease in ocular inflammation over time after SCS TA administration (p<.004). Adverse effects after injections occurred in <20% of the horses at follow-up, but some of these effects were attributed to chronic inflammation prior to effective treatment, long-term topical corticosteroid use, or complications from hospitalization rather than the SCS injections. Most horses (86.7%) in this study remained visual greater than 3months after SCS injection. Based on these results, SCS TA injections appear to be a safe and possible effective treatment modality for managing poorly responsive ERU; further clinical study is warranted.