Objective: To determine the ACV susceptibility in Thai HSV clinical isolates.

Material and Method: One hundred thirty HSV isolates from the Virology Laboratory Unit, King Chulalongkorn
Memorial Hospital, Bangkok, Thailand had typing done by immunofluoresent assay using monoclonal antibody
specific to either HSV-1 or HSV-2. Their sensitivity to ACV (IC50) was determined by plaque reduction assay.

Results: The IC50 of 77 HSV-1 isolates ranged from 0.07-0.97 μg/ml and that of 53 HSV-2 isolates was 0.13-1.66
μg/ml. The standard HSV-1 (KOS) and HSV-2 (Baylor 186) were included in each run. The mean + standard
deviation (SD) of ACV IC50 among HSV-1 and HSV-2 isolates were 0.38 + 0.23 and 0.50 + 0.32 μg/ml while
that of standard HSV-1 and HSV-2 were 0.45 + 0.13 and 0.57 + 0.04 μg/ml. Statistically significant difference
between IC50 of HSV-1 and HSV-2 isolates was indicated (p = 0.02).

Conclusion: No ACVr HSV has been detected and ACV susceptibility of HSV-2 has more resistance than that of
HSV-1.

Keywords: HSV, Acyclovir susceptibility, King Chulalongkorn Memorial Hospital