PURPOSE The goal of this study was to use multiple quantitative disease measures to evaluate the effect of various viral inocula on the development of vaccinia keratitis in rabbits.
METHODS Trephined eyes of female rabbits were infected with 10(4), 10(5), 10(6), or 10(7) plaque-forming units (pfu) of the Dryvax strain of the vaccinia virus and scored daily for disease for 14 days according to a modification of the MacDonald-Shadduck scoring system. Ocular viral titers and vaccinia-specific antibody titers were determined by plaque assay and ELISA, respectively.
RESULTS The amount of virus used for infection affected the severity of disease, with 10(4) pfu eliciting milder keratitis after delayed onset compared with higher amounts of virus. At inocula above 10(5) pfu the course and severity of corneal disease was not significantly different. The time to reach peak titers was delayed in the 10(4) group but peak titers were similar in all groups. Severe conjunctival chemosis interfered with scoring in animals infected with 10(6) or 10(7) pfu. Virus-specific antibody titers were similar in all groups at day 14. Body weights decreased less than 10% in all groups.
CONCLUSIONS The course of vaccinia keratitis in rabbits paralleled that in humans. A viral inoculum of 10(5) pfu/eye was determined to be optimal for use in further studies of vaccinia keratitis.