Chronic ocular Chlamydia trachomatis infection in rabbits: clinical and histopathological findings in the posterior segment.

Purpose: To investigate clinical and histopathologic manifestations of Chlamydia trachomatis (CT)-induced chronic posterior segment (PS) inflammation in rabbits.
Methods: Fifteen rabbits were divided into three equal groups of CT subconjunctival-only (SC) and subconjunctival plus intravitreal (SC+IV) inoculation, and controls. Both noncontrol groups received a bilateral SC injection (BSI) and the SC+IV group additionally received a unilateral IV injection (UII) of CT L2 culture, whereas the controls received a BSI+UII of phosphate-buffered saline. During 6 months post injection, the animals were investigated for PS inflammation and infection clinically and microbiologically (cell culture, ELISA, and real-time PCR). Hematoxylin-eosin staining and direct immunofluorescence in situ reaction were used to reveal the signs of tissue inflammation and infection.
Results: In the SC group, mild PS disorders (eight eyes) involving vitreal infiltration, the following posterior vitreous detachment and chorioretinitis, and severe PS disorders (two eyes) in the form of panuveitis, were developed. In the SC+IV group, mild (three and three eyes that received SC-only and SC+IV injections, respectively) and severe (two and two eyes that received SC-only and SC+IV injections, respectively) PS disorders were developed. A high titer (1:32-1:128) of CT-specific IgM antibody was present in sera from all the noncontrol animals. The CT antigen was detected in the conjunctiva and PS structures (the vitreous, retinal pigment epithelium, and choroid) in 100% and 40% to 75% of all the noncontrol animals, respectively.
Conclusions: Conjunctival or intraocular inoculation with CT may result in invasion of the PS structures and durable persistence thereof, with the development of inflammatory and then degenerative changes. These data might advocate for expanding the role of chronic CT infection in etiology and pathogenesis of vitreoretinal disorders.