Background: The incidence and clinical significance of herpes simplex virus type 1 (HSV-1) acyclovir resistance were determined in patients with recurrent herpetic keratitis (RHK). Methods: Sequential corneal isolates (np39) from 15 immunocompetent patients with RHK were assayed for acyclovir susceptibility and genotyped by analyzing the hypervariable regions of the HSV-1 genes US1 and US12. The thymidine kinase (TK) gene of each isolate was sequenced, and the proportion of acyclovir-resistant viruses within isolates was determined. Results: Uniform acyclovir-resistant or acyclovir-sensitive sequential isolates were identified in 4 and 2 patients, respectively. Notably, the acyclovir susceptibility of sequential isolates changed from acyclovir sensitive to acyclovir resistant (5 patients) or from acyclovir resistant to acyclovir sensitive (3 patients). The acyclovir-resistant phenotype of the isolates correlated with the patients unresponsiveness to acyclovir therapy. Combined analyses of the TK gene and genotype of sequential isolates showed that acyclovir-sensitive isolates contained multiple acyclovirresistant variants of the same virus and that an identical acyclovir-resistant HSV-1 strain reappeared in the patients cornea during RHK episodes. Conclusions: Corneal HSV-1 isolates are mixtures of acyclovir-sensitive and acyclovir-resistant viruses that share the same genotype but have different TK sequences. Recovery of the same acyclovir-resistant virus during consecutive herpetic keratitis episodes suggests that acyclovir-resistant HSV-1 establishes latency and reactivates intermittently to cause acyclovir-refractory RHK. 2009 by the Infectious Diseases Society of America.

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Duan, R, de Vries, R.D, van Dun, J.M, van Loenen, F.B, Osterhaus, A.D.M.E, Remeijer, L, & Verjans, G.M.G.M. (2009). Acyclovir susceptibility and genetic characteristics of sequential herpes simplex virus type 1 corneal isolates from patients with recurrent herpetic keratitis. The Journal of Infectious Diseases, 200(9), 1402–1414. doi:10.1086/606028