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In order to investigate the mechanism of recurrence in herpes simplex keratitis, it is very important to establish an animal model. As a first step, mice were examined with the slit-lamp biomicroscope to determine whether they spontaneously showed recurrent epithelial keratitis after healing of primary herpetic keratitis. Among 90 eyes of 45 inbred C57BL/6 mice, recurrent epithelial keratitis stained with fluorescein was observed in 10 eyes of 9 mice during the observation period up to 50 days after the primary corneal infection with herpes simplex virus (HSV) type I Amakata strain (virulent strain). Recurrent epithelial keratitis was observed in 17 eyes of 15 mice among 116 eyes of 58 ddy mice infected with HSV-I Ska strain (avirulent strain). The epithelial lesions showed punctate or dendritic patterns and continued for one to 7 days. HSV antigen was detected by the fluorescent antibody technique in the cornea of 5 out of 8 eyes which showed recurrent epithelial keratitis using another ddy mice group tested. It was limited in the epithelium of the cornea. These results show that mice herpetic keratitis recurs spontaneously.

Thirty-five clinical isolates of herpes simplex virus type 1 (HSV-1) from 34 patients (35 eyes) with herpetic keratitis were examined in vitro for 5-iodo-2'-deoxyuridine (IDU) and acyclovir (ACV) sensitivity. In addition, the effect of clinical treatment with these two drugs in herpetic keratitis was also investigated. The viral effective dose50 (ED50) was defined as the concentration that inhibited the plaque count by 50% compared to the count of the no drug controls. The viral ED50 of IDU ranged from 0.073 to 0.77 micrograms/ml (0.33 +/- 0.16; Mean +/- SD) and that of ACV from 0.0032 to 0.33 micrograms/ml (0.13 +/- 0.11). No virus with markedly diminished sensitivity to IDU and ACV was found. These results suggest that all HSV-1 strains isolated from patients have good sensitivity in vitro to antiviral agents.