CLINICAL AND PATHOLOGICAL FEATURES OF EXPERIMENTAL ACANTHAMOEBA KERATITIS IN RABBITS

Experimental Acanthamoeba keratitis was induced in 24 female Dutch rabbits to examine the clinical effects of infecton in the eye and to study the usefulness of a new histopathological technique for evaluating rabbit models of this infection. One eye of each animal in group A or B received an instillation of 1.3 X 104 (group A) or 1.3 X 105 (group B) amoeba cysts/eye; phosphate-buffered saline (PBS) solution was instilled into the contralateral eye as the control; animals in groups C and D received intrastromal injections of 5.0 X 103 (group C) or 1.5 X 104 (group D) cysts/eye in one eye and injection of an equal volume of PBS in the contralateral eye. Animals were observed daily for 5 to 84 days. Two rabbits in group D were killed on day 5 and enucleated eyes were embedded in paraffin and stained with hematoxylin-eosin or iodine-potassium iodide. In groups A and B, clinical signs of corneal injury disappeared by 4 hours after inoculation and signs of infection disappeared by day 2. In contrast, all eyes that had been injected with Acanthamoeba (groups C and D) developed severe keratitis, including keratoneuritis and corneal ulcer, followed by neovascularization or corneal perforation. Histologic examination showed infiltrates of leukocytes, lymphocytes, eosinophils, plasmacytes and spindle-shaped cells. The most extensive cell infiltration, and also exocytosis, liquefaction degeneration and intrastromal trophozoites, were seen in the limbic conjunctiva and palpebral conjunctiva. In addition, there was evidence of migration of inflammatory cells to the ciliary body and intravitreal space. This study showed that injection of Acanthamoeba into corneal stroma causes severe infection of the cornea and other eye tissues and that iodine-potassium iodide staining of paraffin embedded specimens is useful to detect Acanthamoeba trophozoites and cysts.