Chronic Intraocular Leptospiral Infection Relying on Biofilm Formation inside the Vitreous Cavity Leads to Recurrent Uveitis in Horses

Abstract

Equine recurrent uveitis (ERU) is a disease known and feared for centuries, as it almost always leads to blindness even with careful and meticulous conservative treatment of the individual episodes of uveitis. In about one-third of horses, both eyes are affected, often necessitating euthanasia. A link between ERU and leptospiral infection has been suspected for nearly 80 years. Vitreous lavage (vitrectomy) can preserve vision in affected eyes. After surgery, no further episodes of uveitis occur in up to more than 95% of operated eyes. With routine performance of vitrectomies, numerous vitreous samples could be used for further investigations. Intraocular anti-Leptospira antibody production was proven, leptospires could be cultured from the vitreous samples, and the LipL32 gene could be detected in the vitreous samples by PCR. Thus, there was convincing evidence of a chronic intraocular leptospiral infection, which can be eliminated most reliably by vitrectomy. Recently, it has been shown that the intraocular leptospires produce biofilm in the equine vitreous. Biofilm formation explains not only the success of vitrectomy, but also the survival of leptospires in the vitreous cavity for many years despite the presence of high intraocular antibody titers and immunocompetent cells, as well as the high tolerance to antibiotics.