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

Abstract

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.

A global one health perspective on leptospirosis in humans and animals

“…This was based on an apparent lack of detectable spirochetes in the eye, evidence of molecular mimicry in some studies, poor response to antimicrobial therapy, and response to glucocorticoid treatment. 37 However, a 2021 study 38 from Germany that examined equine eyes after vitrectomy indicated that biofilm formation within the eye may explain resistance to systemic antimicrobial therapy.…”

Analysis of 1840 Equine Intraocular Fluid Samples for the Presence of Anti-Leptospira Antibodies and Leptospiral DNA and the Correlation to Ophthalmologic Findings in Terms of Equine Recurrent Uveitis (ERU)—A Retrospective Study

“…The preliminary report and a careful clinical and ophthalmologic examination allow an etiologic diagnosis of uveitis in most cases [1]. In addition to traumatic uveitis, which typically occurs only once [2,3], there is also chronic insidious uveitis (e.g., uveitis in leopard coat pattern horses [3][4][5], phacogenic uveitis [6], chronic iritis [1,7] or tumor-associated uveitis [8][9][10], therapy-resistant uveitis (e.g., in intraocular parasitosis [11,12]) or septicemia-associated uveitis (most frequently in foals with rhodococcosis [13]). Regardless of etiology, each acute uveitis episode requires well-aimed and meticulous conservative therapy [3,10].…”

“…In chronic uveitis, various therapeutic options have been described to prevent progressive damage to intraocular structures and further relapses (e.g., subscleral cyclosporine implants [14] or intravitreal gentamicin injections [15][16][17][18][19]), which, however, should be applied selectively and depending on the etiology of the uveitis [1].…”

“…Typical equine recurrent uveitis (ERU) is characterized by painful recurrent episodes of uveitis at unpredictable intervals [3,20] and is caused by a chronic intraocular leptospiral biofilm infection [1,21]. Most equine eyes affected with ERU will lose vision over time unless further episodes of uveitis can be prevented [3,22].…”

“…Most equine eyes affected with ERU will lose vision over time unless further episodes of uveitis can be prevented [3,22]. In about one-third of horses, both eyes are affected [1,23]. The incidence of ERU in Europe is reported to be 7-10% [24,25].…”