Equine uveitis: a UK perspective

Risk factors for a first episode of primary uveitis in the UK and proportion of cases that experience recurrence following this first episode

BACKGROUND

Risk factors for a first episode of primary uveitis in horses have not been determined. In addition, disease progression and the proportion of horses that develop recurrence following the original episode are not known.

OBJECTIVES

To determine the risk factors for the development of a first episode of primary uveitis in horses in the UK and to document the proportion of cases that experience recurrence following this first episode.

STUDY DESIGN

Prospective case-control longitudinal study.

METHODS

Horses with a first episode of primary uveitis between July 2014 and August 2018 were recruited to the study. For each case, two controls were selected. A questionnaire was completed for each horse and multivariable logistic regression analysis was carried out to identify associations between horse and management-level variables and the risk of uveitis. Each case was then followed longitudinally to determine the rate of recurrence of uveitis.

RESULTS

Twenty-three cases and 46 controls were recruited. Being close to a pig farm (OR 27.8, CI 1.31-592.06) and a recent history of flooding of the pasture (OR 15.43, CI 2.80-84.98) was associated with increased risk of uveitis. Being in the same owner's possession for a longer amount of time had a protective effect (OR 0.79, CI 0.68-0.93). Horses recovered uneventfully following treatment and showed no evidence of recurrence in 59.1% of the cases (n = 13). In five horses (22.7%), the initial episode of uveitis could not be controlled and required surgical therapy. Recurrence was observed in four horses (18.2%).

MAIN LIMITATIONS

Small sample size. Recall bias from owners for some of the data. Possibility of selection bias.

CONCLUSIONS

Clinicians can use this information to identify horses with increased risk of uveitis and provide advice to the owners of these horses. The proportion of cases that experience recurrence appears low in the UK.

Infectious Uveitis in Horses and New Insights in Its Leptospiral Biofilm-Related Pathogenesis

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.

Serological Survey of Leptospira Infection in Arabian Horses in Poland

Leptospirosis is one of the most common zoonotic infections worldwide, including in most livestock, some companion animals, horses, wildlife, and humans. Epidemiological estimation of its prevalence in all species is difficult due to the variety of clinical presentations and challenges regarding laboratory diagnosis. The purpose of this study was to measure the seroprevalence of leptospiral infection in Arabian horses kept in the largest breeding farms in Poland, representing over 15% of the Polish Arabian horse population. Leptospira antibodies were detected by MAT (cut-off 1:100) in 33.2% of serum samples (204 of 615 animals) (CI 95%: 29.6–37.0%), most frequently reacting with the serovar Grippotyphosa, similar to previous reports in populations of randomly selected horses. These results indicated high Leptospira seropositivity, thus, although any form of clinical leptospirosis is rare, it may be postulated that the leptospiral exposure is widespread.

The prevalence of uveitis in a population of donkeys in the UK

BACKGROUND

Uveitis is reported to be a leading cause of blindness in horses. Little work has been undertaken to date to investigate whether donkeys are affected by a similar disease prevalence.

OBJECTIVES

To investigate the disease prevalence of uveitis in a population of donkeys in the UK.

STUDY DESIGN

Descriptive observational study.

METHODS

An ophthalmic examination was performed on each donkey, in a darkened stable. Each donkey underwent slit lamp biomicroscopy, and direct and/or indirect ophthalmoscopy. Fluorescein staining, STT1 and IOPs were measured when deemed clinically necessary. Pharmacological pupillary dilation was achieved using 1% tropicamide.

RESULTS

A total of 207 donkeys were examined: 139 males (67.1%) and 68 females (32.9%). Age range was 2-37 years (median: 17 years, interquartile range: 9-25 years). Three donkeys (1.5%) were blind in one eye, and one was monocular at the time of examination. Signs consistent with either previous or current uveitis were identified in eight eyes of six animals (2.9%). Clinical signs included are as follows: miosis (n = 1), corpora nigra atrophy (n = 6), anterior lens capsule pigment (n = 2), cataract (n = 8), posterior synechiae (n = 3), lens subluxation (n = 1), vitreal changes (n = 2), peripapillary scarring (n = 3) and phthisis bulbi (n = 1). Significant ocular pathology precluded fundic examination in three eyes. Three out of eight eyes (37.5%) were blinded by the pathology. The risk of uveitis was found to increase with age (OR 1.1, CI: 1.01-1.25) on univariable analysis (P = .046.).

MAIN LIMITATIONS

Fluorescein staining, tonometry and Schirmer tear test measurements were not performed on all donkeys.

CONCLUSIONS

The disease prevalence reported here is comparable to that reported for horses in the UK. Larger prospective studies are necessary to determine whether there is a similar trend in disease prevalence in the donkey population worldwide. In addition, further investigations should aim to establish whether uveitis in donkeys is similar to the ERU syndrome seen in horses.

Neutrophil Extracellular Traps in the Pathogenesis of Equine Recurrent Uveitis (ERU)

Equine recurrent uveitis (ERU) is considered one of the most important eye diseases in horses and typically appears with relapsing inflammatory episodes without systemic effects. Various disorders have been described as an initial trigger, including infections. Independent of the initiating cause, there are numerous indications that ERU is an immune-mediated disease. We investigated whether neutrophil extracellular traps (NETs) are part of the ERU pathogenesis. Therefore, vitreous body fluids (VBF), sera, and histological sections of the eye from ERU-diseased horses were analyzed for the presence of NET markers and compared with horses with healthy eyes. In addition, NET formation by blood derived neutrophils was investigated in the presence of VBF derived from horses with healthy eyes versus ERU-diseased horses using immunofluorescence microscopy. Interestingly, NET markers like free DNA, histone-complexes, and myeloperoxidase were detected in higher amounts in samples from ERU-diseased horses. Furthermore, in vitro NET formation was higher in neutrophils incubated with VBF from diseased horses compared with those animals with healthy eyes. Finally, we characterized the ability of equine cathelicidins to induce NETs, as potential NET inducing factors in ERU-diseased horses. In summary, our findings lead to the hypothesis that ERU-diseased horses develop more NETs and that these may contribute to the pathogenesis of ERU.

Equine uveitis in the UK: a retrospective study (2008-2018)

BACKGROUND

Uveitis appears to be less prevalent in the UK compared with other parts of the world and studies characterising the disease in the UK are lacking. The objectives of this retrospective study were to describe acute and recurrent cases presenting for management of uveitis in a referral hospital on the North West of England and compare the signalment of horses presenting with uveitis with the equine hospital population during the same period.

METHODS

Medical records of horses presented to the referral Equine Hospital, University of Liverpool with signs of uveitis between 2008 and 2018 were reviewed and clinical details extracted.

RESULTS

Seventy horses presented with uveitis; 33 were classified as acute and 37 as recurrent cases. Sixteen of the horses were affected bilaterally. More bilateral cases were classified as recurrent than acute (P=0.04). No differences in age or sex were noted between acute and recurrent cases, or between cases and the general hospital population. Warmbloods and Appaloosas were over-represented when compared with the general hospital population (P<0.001). Twenty-one horses (30 per cent, 95 per cent CI 20.5 to 41.4) underwent surgery for the control of the uveitis. Fourteen of the 70 horses (20.0 per cent, 95 per cent CI 12.3 to 30.8) underwent enucleation.

CONCLUSION

While relatively uncommon in the UK, uveitis can affect horses from a relatively young age. The disease appears to have a relatively higher frequency than expected in Warmbloods and Appaloosas. It is more likely that a recurrent case will have both eyes affected.

The prevalence of ocular diseases in polish Arabian horses

Background

Equine ocular diseases pose a medical challenge due to long-lasting and cost-consuming therapies as well as economic issues associated with potential decrease in value of affected horses. The scale of the problem is significant but difficult to precisely define because epidemiological data is limited and lacks consistency in presentation. To date, no retrospective studies specifically investigating Arabian horses have been published.

Results

The aim of this cross-sectional study was to investigate the prevalence of ocular lesions and define the ocular diseases present in Arabian horses from breeding farms in Poland. Clinical and ophthalmic examination of 615 Arabian horses at Polish breeding farms (15% of Arabian population in Poland) were performed and medical history from the previous 5 years was analyzed. Data was obtained from review of veterinary archives and epidemiological interview of the resident veterinarian at each farm. The prevalence of ocular diseases was 9.75%. The following pathologies were diagnosed (with their respective prevalence): equine recurrent uveitis (ERU; 5.5%); cataract not related to ERU (3.3%); non-visual eyes (1.13%); posttraumatic lesions (0.8%); glaucoma (0.16%).

Conclusions

In this study, ERU was the most common ocular disease identified in Arabian horses in Poland. Its prevalence was lower than usually reported in Europe and the United States. There was no sex or farm predisposition but ocular disease prevalence increased with age. Other severe ocular pathologies were also observed, confirming that ocular diseases remain an important clinical problem.

Electronic supplementary material

The online version of this article (10.1186/s12917-017-1252-8) contains supplementary material, which is available to authorized users.

The role of Leptospira spp. in horses affected with recurrent uveitis in the UK

BACKGROUND

Equine recurrent uveitis (ERU) is a common cause of ocular pain and blindness in horses. Leptospira spp. have been commonly implicated in the pathophysiology of ERU in mainland Europe and the USA. No recent studies have been carried out in the UK, but Leptospira is reported not to be a major factor in the aetiology of ERU in the UK.

OBJECTIVES

To establish the prevalence of Leptospira-associated ERU in the UK and to identify the serovars involved in these cases; to compare serum vs. aqueous humour antibody levels in cases and controls in order to confirm the diagnosis of Leptospira-associated ERU, and to assess the usefulness of serology alone as a confirmatory test for Leptospira-associated ERU in the UK.

STUDY DESIGN

Case-control study.

METHODS

Eyes enucleated for clinical reasons in ERU-affected horses were collected. Blood and aqueous humour were obtained to determine antibody levels against a variety of Leptospira serovars and C-values (aqueous humour value/serum value) were calculated. In addition, eyes, blood and aqueous humour were obtained from control cases for comparison. Histopathology was performed in all eyes to confirm uveitis in each case. Differences in seroprevalences between ERU and control cases and between Leptospira- and non-Leptospira-associated ERU cases were calculated.

RESULTS

A total of 30 ERU and 43 control eyes were analysed. Of the ERU eyes, only two had a C-value of >4 (prevalence of Leptospira-associated uveitis: 6.7%). Serovars hardjo and javanica were detected. There was no difference in seroprevalence between horses with uveitis and control cases (65.5% and 41.9%, respectively; P = 0.11) or between Leptospira- and non-Leptospira-associated uveitis cases (100% and 63.0%, respectively; P = 0.52).

MAIN LIMITATIONS

The study was limited by low case numbers. Eyes were presented at different stages of disease. The only test used to detect Leptospira was the microscopic agglutination test.

CONCLUSIONS

Leptospira-associated ERU is uncommon in the UK. Serology alone may not help to definitively diagnose Leptospira-associated uveitis in this country.

Medical and Surgical Management of Equine Recurrent Uveitis

Equine recurrent uveitis (ERU) is characterized by recurrent bouts of inflammation interrupted by periods of quiescence that vary in duration. There is little consensus on the clinical manifestations, the underlying causes, or the management. The 3 commonly recognized syndromes of ERU (classic, insidious, and posterior) do not accurately separate the clinical manifestations of disease into distinct categories. An accurate diagnosis and early intervention are essential to minimizing the effects of disease and preserving vision. There are multiple medical and surgical options for controlling ERU as long as the disease is recognized early and targeted treatment is initiated immediately.

Multiple etiologies of equine recurrent uveitis--A natural model for human autoimmune uveitis: A brief review

Equine recurrent uveitis (ERU) has various etiologies, with Leptospira infection and genetic predisposition being the leading risk factors. Regardless of etiology, expression of ocular proteins associated with maintenance of the blood-ocular barrier is impaired in ERU. The recurring-remitting cycle of ERU repeatedly disrupts the blood-ocular barrier, allowing the previously immune-privileged ocular environment to become the site of a progressive local autoimmune pathology that ultimately results in tissue destruction and vision loss. The immune-mediated process involves humoral and cellular mechanisms. Intraocular antibodies either produced in the eye or that leak through the blood-ocular barrier, are often present at higher levels than in serum and react with antigens in ocular tissue of horses with ERU. Ocular infiltration of auto-aggressive lymphocytes occurs with each uveitis episode and is the most crucial contributor to inflammation and eye damage. Recurring uveitis episodes may be initiated when epitopes of an ocular antigen become visible to the immune system (intramolecular spreading) or another autoantigen (intermolecular spreading), resulting in a new inflammatory reaction.

Equine recurrent uveitis: Human and equine perspectives

Equine recurrent uveitis (ERU) is a spontaneous disease characterised by repeated episodes of intraocular inflammation. The epidemiology of ERU has not been fully elucidated, but the condition appears to be much more common in horses than is recurrent uveitis in humans, especially in certain breeds and geographical regions. Both humans and horses show a similarly altered immune response and a marked autoimmune response as the primary disease pathophysiology. However, an inciting cause is not always clear. Potential inciting factors in horses include microbial agents such as Leptospira spp. Microbial factors and genetic predisposition to the disease may provide clues as to why the horse appears so susceptible to this disease. The aim of this review is to discuss the immunology and genetics of ERU, compare the disease in horses with autoimmune anterior uveitis in humans, and discuss potential reasons for the increased prevalence in the horse.

A genome-wide association study identifies risk loci to equine recurrent uveitis in German warmblood horses

Equine recurrent uveitis (ERU) is a common eye disease affecting up to 3-15% of the horse population. A genome-wide association study (GWAS) using the Illumina equine SNP50 bead chip was performed to identify loci conferring risk to ERU. The sample included a total of 144 German warmblood horses. A GWAS showed a significant single nucleotide polymorphism (SNP) on horse chromosome (ECA) 20 at 49.3 Mb, with IL-17A and IL-17F being the closest genes. This locus explained a fraction of 23% of the phenotypic variance for ERU. A GWAS taking into account the severity of ERU, revealed a SNP on ECA18 nearby to the crystalline gene cluster CRYGA-CRYGF. For both genomic regions on ECA18 and 20, significantly associated haplotypes containing the genome-wide significant SNPs could be demonstrated. In conclusion, our results are indicative for a genetic component regulating the possible critical role of IL-17A and IL-17F in the pathogenesis of ERU. The associated SNP on ECA18 may be indicative for cataract formation in the course of ERU.