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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., (© 2022 EVJ Ltd.)

Purpose: 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., Methods: 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)., Results: 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 138 horses, 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% (6/75 horses). The "insidious ERU" type was found in 83% of the ERU cohort (5/6 horses), while "classic ERU" was found in 17% (1/6 horses). 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)., Conclusion: Follicular conjunctivitis, cataracts, and multifocal chorioretinopathy were the three most common ocular abnormalities findings. Icelandic horses who were 8 years or older had an 8% prevalence for ERU. Summer eczema and coat color were not associated with evidence of ERU or other ocular abnormalities., (© 2021 American College of Veterinary Ophthalmologists.)

Objective: To evaluate leptospiral antibody prevalence in 65 horses with ERU and compare outcome in 36 surgically treated eyes (2010-2015)., Procedures: Retrospective data analysis of horses with ERU (n = 65). C-value calculation with microagglutination assay titer (MAT) results for Leptospira spp. Evaluation of follow-up data after pars plana vitrectomy (PPV, n = 21 eyes) and suprachoroidal cyclosporine device implantation (SCDI, n = 15 eyes). Differences between groups were statistically analyzed using Fishers exact test, significance set at P < .05., Results: Positive leptospiral titers were found in 28/65 blood, 31/65 aqueous humor (AH), and 19/20 vitreal (post-PPV) samples. The most common intraocular serovars were Leptospira interrogans grippotyphosa, pomona, and bratislava. Intraocular antibody production was suspected in samples of 22 horses (c-values > 1). Mean follow-up of surgical cases was 3.8 years (PPV) and 3.4 years (SCDI). PPV was performed in 21 eyes with positive, SCDI in 15 eyes with negative leptospiral test results. Uveitis recurred less often after PPV (2/21) compared to SCDI (6/15, P = .04). Retinal detachment occurred after PPV only (5/21, SCDI 0/15, P = .06), whereas only SCDI-treated eyes were enucleated (PPV 0/21, SCDI 3/15, P = .06). Blindness or visual impairment was equally likely to occur in both treatment groups after surgery (PPV 7/21, SCDI 7/15, P = .5)., Conclusions: Leptospiral antibody prevalence is high in horses with ERU in Switzerland. Recurrence of uveitis is uncommon following PPV in the present study; an increased risk of retinal detachment exists. Enucleation is more often warranted in horses after SCDI in this study due to a higher uveitis recurrence., (© 2020 American College of Veterinary Ophthalmologists.)

Background: Equine recurrent uveitis (ERU) has been associated with Leptospira spp. infection. No information exists concerning the prevalence of Leptospira-associated ERU in Belgium and about the sensitivity of detection of Leptospira in different ocular media., Objectives: To establish the prevalence of intraocular Leptospira spp. in ERU-affected and healthy eyes of horses examined at the Equine Clinic of the University of Liège by real-time PCR and to compare the results of the aqueous and vitreous humour of the same eye., Study Design: Cross-sectional., Methods: Sixty-six eyes from 59 client-owned horses with a diagnosis of equine recurrent uveitis (ERU-group) were studied from May 2015 to December 2017. Fifty healthy eyes from 28 euthanised horses for unrelated reasons examined during the same period were included in the control group. Intraocular fluids (aqueous and/or vitreous humours) from ERU-affected eyes were sampled and analysed by real-time PCR for Leptospira spp. Aqueous and vitreous humours from the control group were processed in the same way., Results: Both groups were comparable regarding age, sex, eye sampled (OS/OD), humours sampled (aqueous/vitreous humour) but not regarding breeds, with an over-representation of Warmbloods and Appaloosas in the ERU-group. The prevalence of Leptospira spp. was 30.3% (20/66 eyes) in the ERU-group. Leptospira spp. DNA was identified in 11 aqueous and 17 vitreous humours with eight horses testing positive in both humours, nine horses testing positive for vitreous humour alone and third horses for aqueous humour alone. The phi-correlation between aqueous and vitreous humour Leptospira-PCR results is 0.47 suggesting a low association. All the control eyes were negative., Main Limitations: The diagnostic method selected for this study (lipL32 qPCR) did not allow identification of the serovars., Conclusions: Leptospirosis is a potential cause of ERU in Belgium. Testing both intraocular media is advised whenever possible. The Summary is available in Spanish - see Supporting Information., (© 2018 EVJ Ltd.)

A recently purchased 16-year-old Thoroughbred mare with a history of recurrent colic and low body weight, also had lameness in 3 limbs, pain at the sacro-iliac joint, and increased corneal opacity of the right eye. Response to supportive therapy was poor and euthanasia was elected. A postmortem examination and histopathology confirmed cyathostomiasis within the large colon and cecum and chronic anterior uveitis of the right eye., Competing Interests: Use of this article is limited to a single copy for personal study. Anyone interested in obtaining reprints should contact the CVMA office (hbroughton@cvma-acmv.org) for additional copies or permission to use this material elsewhere.

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., (© 2017 The Authors. Equine Veterinary Journal published by John Wiley & Sons Ltd on behalf of EVJ Ltd.)

In the ongoing discussion regarding the aetiopathogenesis of equine recurrent uveitis (ERU) it was the aim of the present study to elucidate the relationship of leptospira infection and ERU. In a population of 225 horses leptospira were examined in vitreous humor by culture and leptospira antibody were detected in vitreous humor and serum samples. Preoperative serum samples were collected from 221/225 ERU patients of different age, gender and breed. Undiluted vitreous humor was aseptically taken from 198/225 patients that underwent pars plana vitrectomy at the beginning of surgery and from 27/225 patients' eyeball after enucleation: Serum and vitreous humor were tested for specific leptospiral antibodies by microscopic agglutination test (MAT). Furthermore, vitreous humor was examined by culture. 20 patients which were euthanized due to a live-threatening disease other than ERU served as a control group. A total of 127/221 (57.5%) horses had serum antibodies (≥ 1:100). Most frequently antibodies against L. interrogans serovar Grippotyphosa were detected (79/127), followed by L. interrogans serovar lcterohaemorrhagiae (34/127) and L. interrogans serovar Bratislava (29/127). Only 79/225 horses (35.1%) had leptospiral antibodies in vitreous humor, in which L. interrogans serovar Grippotyphosa (67/79) was identified most frequently followed by L. interrogans serovar Pomona (18/79) and L. interrogans serovar lcterohaemorrhagiae (8/79) which was identified as single or multiple reaction. Isolation of leptospira from vitreous humor was positive in 34/212 horses (16%). 10/20 control horses had a positive antibody titer against leptospira in serum and 2/20 horses in vitreous humor, whereas there was no leptospira detected in culture. The result of 84% negative cultures from vitreous humor of 212 ERU patients is decisive for the diagnosis and therapy of ERU.

Leptospirosis is a zoonotic disease of global importance, and has a worldwide distribution. Equine leptospirosis is commonly manifested by recurrent uveitis, reproductive disorders, as abortions, embryonic absorption, stillbirth and the birth of weak foals. The aim of this study was to verify the presence of Leptospira sp or its DNA in genital tract of mares with reproductive problems. A total of 38 mares with reproductive problems were studied. All the mares were sampled for blood (for serology), urine (for culturing and qPCR), vaginal fluid-VF and endometrial biopsy-EB (for culturing, qPCR and indirect immunofluorescence). PCRs products were sequenced for secY gene. Seventeen (44.7%) serum samples were reactive, predominantly against serogroups Australis (76.4%) and Pomona (23.6%). No positive culture was obtained, but DNA was detected by qPCR on urine samples (26.3%), VF (44.7%) and EB (18.4%) collected 2 months or longer following diagnosis of early fetal death and endometritis. Leptospira cell aggregations were visible by indirect immunofluorescence on 57.1% (4/7) EBs and 17.6% (3/17) VFs. A total of 18 amplicons showed interpretable sequences. Out of those 18 amplicons, 15 presented 100% of identity with the species L. interrogans (sv Bratislava and Pomona), while three were L. borgpertersenii. This study suggests the presence of leptospires in the uterus of mares with reproductive problems. Moreover, serology was shown not to be indicated for the diagnosis of presumptive Leptospira infection in early gestation. The most common agent of the genital infection in those mares was L. interrogans, most probably sg Australis., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Leptospirosis in horses has been considered a relatively uncommon infection. However, recent data suggest that the infection is widespread, with the incidence and infecting serovars varying considerably in different geographical regions. The majority of infections remain asymptomatic. Clinical signs in equine leptospirosis resemble those seen in other animal species. However, leptospirosis as a cause of acute respiratory distress is becoming more frequently recognised. A particular feature of equine leptospirosis is post infection recurrent uveitis (moon blindness or periodic ophthalmia), which appears to be mediated by autoimmune mechanisms involving cross reactivity between ocular tissues and leptospiral membrane proteins. There are no leptospiral vaccines licensed for use in horses, with no prospect for any becoming available in the foreseeable future. Accordingly, prevention of equine leptospirosis must rely on good hygiene practices, minimisation of rodent contact, and vaccination of other species of production and companion animals., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Screening of an expression library of Leptospira interrogans with eye fluids from uveitic horses resulted in identification of a novel protein, LruC. LruC is located in the inner leaflet of the leptospiral outer membrane, and an lruC gene was detected in all tested pathogenic L. interrogans strains. LruC-specific antibody levels were significantly higher in eye fluids and sera of uveitic horses than healthy horses. These findings suggest that LruC may play a role in equine leptospiral uveitis.

A 7 yr old castrated male Australian shepherd dog was examined for acute change in iris color, lethargy, and anorexia. Uveitis, acute renal failure, and presumed cholecystitis were diagnosed. Based on clinical findings, leptosporosis was suspected, and the dog was treated with antibiotics and supportive care. The dog made a complete recovery, and leptospirosis was confirmed on convalescent titers. Due to the zoonotic potential, leptospirosis should be considered in cases of uveitis, as well as possible cholecystitis.

Reason for Performing Study: Information on antibiotic concentrations in the equine eye following systemic therapy is limited. Reports that Leptospira spp. are frequently present in the eyes of horses with recurrent uveitis, emphasises a need for studies on ocular concentrations of specific antibiotics., Hypotheses: 1) Enrofloxacin, administered i.v. at 7.5 mg/kg bwt q. 24 h, results in aqueous humour concentrations greater than the reported minimum inhibitory concentration (MIC) for Leptospira pomona. 2) Aqueous humour paracentesis sufficiently disrupts the blood-aqueous humour barrier (BAB) to cause an increase in aqueous humour protein and enrofloxacin concentrations., Methods: Aqueous humour enrofloxacin and total protein concentrations were determined in 6 healthy, mature horses after i.v. administration of enrofloxacin. Paracentesis was performed on the left eye on Days 3 and 4, 1 h following enrofloxacin administration, to determine enrofloxacin concentrations in healthy eyes and in eyes with mechanical disruption of the BAB. Paracentesis was also performed on the right eye 23 h after enrofloxacin administration. Blood samples were collected from the horses at identical times to determine enrofloxacin aqueous humour:plasma ratios., Results: Mean +/- s.d. enrofloxacin concentration in the aqueous humour 1 h post administration on Day 3 was 0.32 +/- 0.10 mg/l (range 0.18-0.47); and aqueous humour enrofloxacin, total protein and aqueous humour:plasma enrofloxacin ratios were higher on Day 4 than Day 3., Conclusions and Potential Relevance: Following disruption of the BAB, enrofloxacin concentrations were above the reported MIC for Leptospira pomona.

This study documents the examination of 17 horses (both sexes, 3-18 years old) suffering from spontaneous equine recurrent uveitis (ERU). Vitreal samples obtained by pars plana vitrectomy were examined macroscopically and ultrastructurally, and in most cases also by cultural examination, by microscopic agglutination test (MAT) and by polymerase chain reaction. In 24% (4/17) of the animals, ultrastructural examination by electron microscopy revealed intact leptospiral bacteria in the vitreous. The leptospires were detected freely in the vitreous and also incorporated by a phagocyte. They were surrounded by a rim of proteinaceous material which was reduced around a phagocytosed leptospira. Ninety-four per cent (16/17) of the vitreal samples presented significant antibody levels in the MAT, mostly against leptospiral serovar Grippotyphosa. Seventy-five per cent (9/12) of bacterial culture examinations were positive for leptospira. Polymerase chain reaction was positive in all (16/16) examinations performed. Our findings support previous reports suggesting that leptospires play an important role in the pathogenesis of ERU. Interestingly, this study found leptospires after secondary and later acute episodes. A persistent leptospiral infection is therefore suggested as the cause of ERU.

Equine recurrent uveitis (ERU) is caused by persistent intraocular leptospira, which appear to use the vitreous body as a refuge. The detection of leptospira in the vitreous body of horses with spontaneous ERU by histological methods has not yet been described. Thirty eight vitreous body samples from 36 horses with ERU (collected during vitrectomy), and 10 vitreous body samples obtained from 5 horses without ocular disease (control group) were examined by transmission electron microscopy. Prior to sample collection, 2 ml of a leptospira culture suspension were injected into the vitreous body of 2 eyes enucleated from horses of the control group. The detection of leptospira in samples, experimentally inoculated with these bacteria was uncomplicated; in vitreous body samples from horses with spontaneous ERU the detection was successful in only a few cases (3/38). The morphologically varying envelope of leptospira in vitreous body samples of horses which developed ERU spontaneously suggests the existence of a bacterial masquerade in vivo.

Objective: To evaluate the effect of vaccination against leptospirosis on frequency and days to recurrence of uveitis and progression of disease in horses with equine recurrent uveitis (ERU)., Animals: Forty-one horses with ERU., Procedure: Horses were randomly assigned to experimental (vaccinated) or control groups. Vaccine containing six serovars of Leptospira or placebo was administered, an ophthalmic examination performed and blood samples drawn on days 0, 28, 180 and 365. Antibody titers were measured against each serovar. Recurrence of uveitis was verified by ophthalmic examination. Results of the initial and final ophthalmic examinations were compared and progression of disease defined as an increase in extent of synechiae, or development of new or progression of an existing cataract., Results: Vaccination increased the average geometric mean serum antibody titer from 225 on day 0, to 4077 and 593 on days 28 and 180, respectively. After the second vaccination, days to first recurrence was significantly longer (median 126 days; range 24-231 days) when compared with controls (median 86 days; range 14-192 days, P=0.04). Recurrence of ERU was observed among 7/20 (35%) vaccinated horses and 12/21 (57%) controls; however, this difference was not statistically significant (P=0.061, OR 0.25, 95% CI 0.06, 1.07). More horses in the experimental group 13/20 (65%) experienced progression of disease when compared with controls 12/21(57%); however, this difference was statistically nonsignificant (P=0.35)., Conclusions: Vaccine significantly increased days to recurrence, but failed to slow the progression of disease. These data do not support the use of vaccination against leptospirosis as adjunct therapy for the routine treatment of horses with ERU.

A 2-year-old Thoroughbred filly presented with ocular pain and epiphora of the left eye. The pupil was miotic and the cornea edematous near the ventro-temporal limbus, but did not retain any fluorescein. The topical antibiotics and atropine and diclofenac, and systemic flunixin meglumine and antibiotic therapy did not resolve the condition. A pink and fleshy infiltrate developed near the limbus indicating nonulcerative keratouveitis. The anterior uveitis deteriorated as manifested by the presence of dyscoria, hypopyon, and organized fibrin in the anterior chamber. Ocular signs were improved by topical and subconjunctival corticosteroids, but repeatedly deteriorated as the frequency of medication was reduced. The horse was seropositive to three serovars of Leptospira interrogans. The animal was diagnosed as blind on day 91 by the absence of pupillary light and menace reflexes, and donated for histopathologic diagnosis. The corneal opacity was histologically fibrotic and infiltrated predominantly by lymphocytes with Descemet's membrane partially disrupted by macrophages. The choroid was infiltrated by lymphocytes, eosinophils and basophils, and was positive to IgG and C3. There were filamentous or spiral structures positive to Warthin-Starry stain in the renal cortex. There was also polymerase chain reaction amplification of the leptospiral gene in the kidney. From these findings nonulcerative keratouveitis was believed to be caused by systemic infection with Leptospira.

Objective: To measure antibody titers against Leptospira interrogans in serum and vitreous humor and determine the prevalence of L interrogans in vitreous humor of horses with recurrent uveitis., Design: Cross-sectional study., Animals: 242 horses (270 eyes) with recurrent uveitis undergoing vitrectomy and 39 control horses (54 eyes) without any history or clinical signs of recurrent uveitis undergoing euthanasia or enucleation for unrelated reasons., Procedure: Serum and vitreous humor were tested for antibodies against 13 serovars of L interrogans. Vitreous humor was submitted for leptospiral culture; isolates were typed to the serogroup level., Results: Leptospira interrogans was isolated from vitreous humor from 120/229 (52%) horses (126/252 [50%] eyes) with recurrent uveitis but was not isolated from vitreous humor from 36 eyes of 21 control horses. Duration of recurrent uveitis was > or = 1 year for 45 of the 120 (38%) horses from which the organism was isolated. Geometric mean antibody titers against L interrogans in the vitreous humor and serum of horses with recurrent uveitis were 1:1,332 and 1:186, respectively. Only 91 of 120 (76%) horses from which the organism was isolated had a 4-fold or greater difference between serum and vitreous humor antibody titers., Conclusions and Clinical Relevance: Results suggest that persistent ocular infection with L interrogans is common in horses with recurrent uveitis. A 4-fold increase in vitreous humor versus serum antibody titers may not be a sensitive test for the diagnosis of L interrogans-induced recurrent uveitis. We hypothesize that the immune component of recurrent uveitis can be directly induced and maintained by persistent infection of the eye with L interrogans.

Leptospiral organisms have long been presumed to be associated with the presence of equine recurrent uveitis. This project was undertaken to determine the presence of Leptospira spp. in the aqueous humor of horses with uveitis to determine if there was an association with inflammation. Thirty horses were determined to have recurrent uveitis based on clinical evaluation or history. Sixteen horses were judged clinically and historically to be free of uveitis and were used as controls. Aqueous humor samples were cultured and evaluated by PCR for the presence of Leptospira DNA. Serum was collected and evaluated for the presence of antibodies against five serovars in a leptospirosis panel. Twenty-one of 30 horses with recurrent uveitis and one of 16 uveitis-free horses were positive by PCR for the presence of Leptospira DNA. Six of these 21 horses with uveitis were culture positive for leptospires from the aqueous humor. Serologic results did not correlate well with the presence of Leptospira DNA or organisms in the aqueous humor. Leptospira spp. are present in a high percentage of horses with naturally occurring recurrent uveitis.

130 vitreous samples, systematically collected in 1998 from 117 horses during vitrectomy, were cultured for the presence of leptospires. All horses suffered from equine recurrent uveitis (ERU), also known as periodic ophthalmia or moon blindness, and were treated surgically to combat painful attacks, and to preserve vision. In 35 out of 130 vitreous samples (35/130 = 26.9%), leptospires could be isolated. These isolates belong to the grippotyphosa serogroup (n = 31) and to the australis serogroup (n = 4). So, for the first time, leptospires were recovered from eyes in vivo in a large number of horses with ERU. Vitreous samples and one serum sample from each horse were also tested for leptospiral antibodies using the microscopic agglutination test (MAT). In 92 vitreous samples (92/130 = 70.7%) and 96 serum samples (96/117 = 82.0%) leptospiral antibodies were detected at a dilution of > 1:100. The presence of intact leptospires and specific antibodies in eyes affected with ERU demonstrates a local antibody production to leptospiral antigen. These results indicate an important etiological role of leptospires in equine recurrent uveitis.

Vitreous samples from 43 horses which underwent vitrectomy because of equine recurrent uveitis (ERU) were cultured for leptospires. Out of 4 vitreous samples (4/43 = 9%), leptospires could be isolated. In 3 cases, serovar grippotyphosa, and in one case, a serovar out of the serogroup Australis were identified. So for the first time, in several horses with ERU in vivo cultures of vitreous material were positive for leptospires. A strong evidence of association between leptospiral infection and uveitis is discussed for many years. In this investigation the leptospiral etiology is confirmed. Vitreous material from 42 and serum samples from 40 horses were tested for specific antibodies to leptospira by microagglutination test (MAT). In 34 vitreous samples (34/42 = 81%), leptospiral antibody titers of 1:50 or higher were detected. In 33 horses (33/40 = 83%) leptospiral antibody titers of 1:50 or higher could also be detected in the serum. Altogether, leptospiral antibodies were detected by the MAT in the serum and in the vitreous material of 39 of 43 horses (= 91%) subjected to vitrectomy. These results indicate, that ERU is probably often a sequel to systemic Leptospira interrogans infection. The presence of intact leptospires and specific antibodies in eyes affected with ERU indicates a local antibody production to leptospira organisms and/or their antigens.

Recurrent uveitis, a leading cause of blindness in horses, often develops as a sequela to systemic leptospirosis. Over a 7-year period, 63 of 112 (56%) horses with uveitis were seropositive for Leptospira interrogans serovar pomona, but only 23 of 260 (9%) horses without uveitis were seropositive. Odds-ratio analysis revealed that seropositive horses were 13.2 times more likely to have uveitis than were seronegative horses. Of the 63 seropositive horses with uveitis, 59% developed blindness, compared with only 24% in the 49 seronegative horses with uveitis that lost vision in 1 or both eyes during the same period. Odds-ratio analysis revealed that seropositive horses with uveitis were 4.4 times more likely to lose vision than were seronegative horses with uveitis. Of the 112 horses with uveitis, 28 (25%) were Appaloosas, compared with only 10 of the 260 (4%) horses without uveitis (odds ratio, 8.3). In addition, 19 of the 28 (68%) Appaloosas with uveitis developed blindness, compared with only 30 of the 84 (36%) non-Appaloosas with uveitis that lost vision in 1 or both eyes (odds ratio, 3.8). This field study therefore confirmed a strong positive relationship between uveitis and leptospiral seroreactivity in horses. Furthermore, the data suggested that seropositive horses with uveitis were at increased risk of losing vision, compared with that in seronegative horses with uveitis, and that Appaloosas were at increased risk of developing uveitis and associated blindness, compared with that in non-Appaloosas.

Equine clinical leptospirosis has been primarily related to uveitis and the often recurrent sequelae of ocular changes. Reports of equine hepatic and renal involvement are sporadic. More recently, serovar bratislava has been identified as a host-adapted serovar in the horse. More significantly, reports of equine abortion and stillbirth have become more frequent in the literature. This is more than likely a result of improved diagnostic techniques, not of increased prevalence of disease. In addition to abortion, equine neonatal disease is becoming more frequently recognized in association with leptospira infection. Whether leptospiral infection results in abortion or diseased foals may depend upon the stage of gestation when the mare is exposed and host immune status. Antibiotic of choice for treatment of equine leptospirosis remains speculative, as specific equine studies have not been performed. Extrapolation from other species suggests that the use of streptomycin remains a good choice of therapy for the chronic shedding state and may be used in combination with other antimicrobials for treatment of acute disease. Penicillin or potentiated penicillins and tetracycline at appropriate to high end dosages are logical choices for the treatment of acute leptospirosis.

C3 was detected bound in vivo to the opaque cornea of horses inoculated with killed Leptospira interrogans. Employing epithelial corneal cells isolated from a monolayer in tissue culture, we proved that C3 is fixed in vitro to the intact cell surface after incubation with a fresh equine anti-Leptospira serum. These findings, in addition to the infiltration of cornea with neutrophils and lymphocytes, may explain the mechanisms of tissue damage in recurrent uveitis of horses with leptospirosis.

The antigenic relationship between Leptospira interrogans, equine cornea and lens was previously noted in our studies. Serum antibodies from horses inoculated with serovars wolffi, pomona, icterohaemorrhagiae, and tarassovi, were able to bind to five antigenic fractions from both cornea and lens, as demonstrated by immunoblotting. These antigens seem to be made up of protein and carbohydrates. After treatment with periodate for cleavage of glycoside ring structures, those fractions kept their condition of target for anti-Leptospira antibodies. Nevertheless, all fractions lost that condition after being subjected to peptide hydrolysis.