Effect of vaccination against leptospirosis on the frequency, days to recurrence and progression of disease in horses with equine recurrent uveitis

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.