Detection of Leptospira interrogans DNA and antigen in fixed equine eyes affected with end-stage equine recurrent uveitis.

Equine recurrent uveitis (ERU) is the most frequent cause of blindness in horses worldwide. Leptospira has been implicated as an etiologic agent in some cases of ERU and has been detected in fresh ocular tissues of affected horses. The objective of this study was to determine the presence of Leptospira antigen and DNA in fixed equine ocular tissues affected with end-stage ERU. Sections of eyes from 30 horses were obtained. Controls included 1) 10 normal equine eyes and 2) 10 equine eyes with a nonrecurrent form of uveitis. The experimental group consisted of 10 eyes diagnosed with ERU based on clinical signs and histologic lesions. Sections were subjected to immunohistochemical staining with an array of rabbit anti-Leptospira polyclonal antibodies. DNA extractions were performed by using a commercial kit designed for fixed tissue. Real-time PCR analysis was completed on extracted DNA. The target sequence for PCR was designed from alignments of available Leptospira 16S rDNA partial sequences obtained from GenBank. Two of 10 test samples were positive for Leptospira antigen by immunohistochemical assay. Zero of 20 controls were positive for Leptospira antigen. All test samples and controls were negative for Leptospira DNA by real-time PCR analysis. Leptospira was detected at a lower frequency than that previously reported for fresh ERU-affected aqueous humor and vitreous samples. Leptospira is not frequently detectable in fixed ocular tissues of horses affected with ERU when using traditional immunohistochemical and real-time PCR techniques.