A molecular method for typing Herpes simplex virus isolates as an alternative to immunofluorescence methods

Background: Typing of Herpes simplex virus (HSV) isolates is required to identify the virus isolated in culture. The methods available for this include antigen detection by immunofluorescence (IF) assays and polymerase chain reaction (PCR). This study was undertaken to standardize a molecular method for typing of HSV and compare it with a commercial IF reagent for typing. Objectives: To compare a molecular method for typing HSV isolates with a monoclonal antibody (MAb) based IF test. Study design : This cross-sectional study utilized four reference strains and 42 HSV isolates obtained from patients between September 1998 and September 2004. These were subjected to testing using an MAb-based IF test and a PCR that detects the polymerase ( pol ) gene of HSV isolates. Results: The observed agreement of the MAb IF assay with the pol PCR was 95.7. Fifty four point eight percent (23/42) of isolates tested by IF typing were found to be HSV-1, 40.5 (17/42) were HSV-2, and two (4.8) were untypable using the MAb IF assay. The two untypable isolates were found to be HSV-2 using the pol PCR. In addition, the cost per PCR test for typing is estimated to be around Rs 1,300 (USD 30), whereas the cost per MAb IF test is about Rs 1,500 (USD 35) including all overheads (reagents, instruments, personnel time, and consumables). Conclusion: The pol PCR is a cheaper and more easily reproducible method for typing HSV isolates as compared to the IF test. It could replace the IF-based method for routine typing of HSV isolates as availability of PCR machines (thermal cyclers) is now more widespread than fluorescence microscopes in a country like India.