Equine recurrent uveitis: A review of clinical assessment and management

Equine recurrent uveitis (ERU) is a vision‐threatening ocular disease that practitioners must be able to identify and manage. Although not every case of acute uveitis will develop into ERU, if 2 or more episodes of uveitis are observed, a diagnosis of ERU can be made. Patient outcomes improve with early diagnosis, appropriate therapy and client education. Recent advances in surgical options and treatment of horses with ERU have improved success in managing this condition. New therapeutic strategies under investigation may further enhance results and reduce the development of complicating factors.     

Equine recurrent uveitis: A clinical manifestation of leptospirosis

Leptospirosis is a zoonosis of worldwide distribution affecting domestic animals, wildlife and man. The bacterial disease is caused by pathogenic Leptospira spp., which are transmitted from reservoir hosts to accidental hosts. Horses are accidental hosts and can become susceptible to leptospiral infections. Widespread exposure to leptospires exists and is significantly more common than clinical disease. Leptospirosis can have different clinical manifestations including abortion, still birth, systemic disease with hepatic or renal dysfunction, and equine recurrent uveitis (ERU). ERU is the most frequently encountered clinical manifestation and this article will focus on the review of leptospira‐associated ERU. Equine recurrent uveitis is the most common cause of vision impairment and blindness in horses. The pathogenesis of leptospira‐associated ERU involves direct bacterial effects and immune‐mediated responses. Clinical signs vary between the acute and chronic phases of the disease and progress over time. The diagnosis of leptospira‐associated ERU can be difficult and usually requires a combination of diagnostic tests. Medical and surgical treatments have been described with varying outcomes. The prognosis for sight is usually poor, although core vitrectomy may improve the outcome. Avoidance of leptospiral exposure of horses is the only reliable prevention of leptospira‐associated disease.     

Equine uveitis.

Uveitis (inflammation of the iris, ciliary body, or choroid) is a potentially blinding condition with a significant economic impact on the horse industry. Variable symptoms are described, as well as a considerable range of structural and functional sequelae. Known causes of initial episodes include bacterial, viral, traumatic, and parasitic insults, with recurrence by immunologic mechanisms. Treatment strategies and management recommendations that may reduce the incidence or severity of episodes are discussed.     

Equine recurrent airway obstruction: pathogenesis, diagnosis, and patient management.

Recurrent airway obstruction is a condition that affects some older horses maintained in confinement. Clinical signs range from exercise intolerance with occasional cough to dyspnea at rest. Bronchoalveolar lavage cytology is characterized by neutrophilic leukocytosis (15%-85%) and is recommended for making the diagnosis in horses with mild to moderate disease. Environmental management combined with periodic bronchodilator and antiinflammatory corticosteroid therapy yields the best prognosis for disease remission.     

Surgical management of equine recurrent uveitis with single port pars plana vitrectomy

Current information suggests that equine recurrent uveitis (ERU) is an immune-mediated reaction to infectious agents or to autologous ophthalmic tissue. Recurrences are associated with progression of irreversible ocular damage. This report describes the intraoperative technique, complications, and long-term results of 38 eyes in 35 horses with ERU that underwent pars plana vitrectomy. The majority of the horses were warm-blooded. Recurrence of ERU was prevented in 35 of the 38 eyes. Some horses, especially in patients with incipient cataracts, developed vision loss in postoperative, quiescent eyes which was usually associated with cataract formation. Vision was stable in 85% of all eyes that underwent vitrectomy. Pars plana vitrectomy in horses appears successful in interrupting the cycle of repeated episodes of ERU, and the subsequent globe destruction in the majority of eyes. Removal of uveitis-induced 'immunologic memory' in the vitreous by vitrectomy may reduce adverse interaction between the vitreous and the uveal tract, and therefore reduce the recurrence of ERU.     

Ocular immunology in equine recurrent uveitis

Equine recurrent uveitis (ERU) is a disease with high prevalence and relevance for the equine population, since it results in blindness. Over the last decade, important advancements have been made in our understanding of the underlying immune responses in this disease. ERU is mediated by an autoaggressive Th1 response directed against several retinal proteins. Interphotoreceptor-retinoid binding protein (IRBP) and cellular retinaldehyde-binding protein (CRALBP) are capable to induce ERU-like disease in experimental horses, with the unique possibility to activate relapses in a well-defined manner. Further, proteomic evidence now suggests that retinal Mueller glial cells (RMG) may play a fatal role in uveitic disease progression by directly triggering inflammation processes through the expression and secretion of interferon-γ. Ongoing relapses in blind eyes can be associated with stable expression of the major autoantigens in ERU retinas. This review briefly summarizes the most significant developments in uveitis immune response research.     

Equine acupuncture methods and applications: A review

This review discusses the applications of acupuncture (AP) and its eastern medical philosophy in equine health, and the main techniques used to stimulate acupoints in equine practice. These methods include dry needling, electroacupuncture (EA), moxibustion, laser therapy, haemopuncture, aquapuncture, pharmacopuncture, acupressure and gold implants.     

Equine recurrent airway obstruction and insect bite hypersensitivity: understanding the diseases and uncovering possible new therapeutic approaches

Recurrent airway obstruction (RAO) and insect bite hypersensitivity (IBH) are allergic conditions that are commonly encountered in the horse. Whilst complete allergen avoidance is an effective management strategy for both diseases, this may not be achievable in all cases and treatment options are therefore required. The inflammatory response is the main therapeutic target for glucocorticoids given to horses with RAO and severe cases of IBH, whilst the bronchodilators used in RAO primarily target airway smooth muscle. Such drugs are effective in most but not all individuals and there may be unwanted adverse effects. This article will review how knowledge of drug action and the pathogenesis of RAO and IBH can be utilised to identify potential targets for novel therapeutic agents that, in the longer term, may be safer and/or more effective in managing the allergic horse.     

Equine emergency upper airway management

Respiratory distress due to acute upper respiratory tract obstruction is an uncommon emergency in equine practice. However, clinicians should be confident with the approach to this truly life-threatening scenario. Clinical signs are obvious at rest and include increased respiratory effort, loud respiratory noise and recumbency as asphyxiation progresses. Many cases of upper respiratory tract obstruction involve the pharynx or larynx, though obstruction in other regions of the upper respiratory tract and other causes of respiratory distress should be considered. Generally, the obstruction can be bypassed by placing a nasotracheal tube under endoscopic guidance or by making a temporary tracheotomy to ensure a patent airway. Following this stabilisation, further investigation into the cause of airway obstruction can be performed. Endoscopy is usually the most valuable diagnostic tool, though other imaging modalities can be useful. Further empirical treatment is often required, though the specific management will vary depending on the pathology present.     

Welfare and management of decreased visual capacities and pain in a pony suffering from equine recurrent uveitis: A clinical case

This clinical case describes a 14-year-old Gypsy Cob gelding presented for suspected impaired vision. Given the apparently insidious presentation, bilateral equine recurrent uveitis (ERU) was strongly suspected. ERU management was addressed both clinically and from a welfare point of view. Treatment using ointment was preferred to eye drops to reduce the frequency of administration. Clicker training was used to facilitate treatment administration by eliciting positive emotions. In response to the progressive bilateral blindness, social and physical environments and new relational practices were adapted to reduce stress on the pony by increasing predictability and controllability of his situation. This case is to our knowledge the first to include detailed welfare management strategies as a part of a more comprehensive medical approach to ERU.     

Equine urine pH: normal population distributions and methods of acidification

Our investigation of the urine of grazing horses at the University of Kentucky shows that the mean pH level is about 7.9, and if their diet is supplemented with grain, it is about 7.4. There appears to be no significant effect of time of day or year on urine pH levels in horses. However, horses taken from pasture and supplemented with grain in a stalled environment show a slight decrease in urine pH. Additionally, we investigated the effects of storage on pH levels. Equine urine samples appear to be quite stable with regard to pH for 48h, but then show a marked increase. Urine pH can have a great effect on the urine concentration of some drugs and therefore, uncertainties can arise when data generated in grazing horses are compared or extrapolated to racing horses whose urine pH can be quite low. In an effort to simulate the drop in urine pH seen in some racing horses, we examined the effects of ammonium chloride, ascorbic acid, lactic acid and methionine on urine pH in research horses. Both oral and intravenous routes of administration were used. Although all agents tested showed varying degrees of efficacy, oral administration of ascorbic acid proved to be the safest and most effective agent to model the rapid acidification of urine seen in post race samples.