Protein A-based ELISA: its evaluation in the diagnosis of herpes simplex encephalitis.

Herpes simplex encephalitis (HSE) represents one of the most severe infectious diseases of the central nervous system. As effective antiviral drugs are available, early rapid and reliable diagnosis has become important. The objective of the present study was to develop a sensitive enzyme-linked immunosorbent assay (ELISA) protocol for herpes simplex virus (HSV) antigen detection by assessing the usefulness of hyperimmune sera isolated from HSV-seropositive patients. A total of 52 cerebrospinal fluid (CSF) and 62 serum samples of HSE patients and non-HSE persons were analyzed. An in-house ELISA protocol utilizing hyperimmune sera was developed for HSV antigen detection. To improve the specificity of the method, protein A was incorporated into the protocol for ELISA. The sensitivity (70% and 90%) of antigen detection was high in CSF and serum samples, respectively, of confirmed HSE patients. However, lower specificity (52.3% and 42.3%), respectively, was obtained, which was improved by using protein A in the ELISA protocol. The modification in the method yielded good sensitivity (80% and 70%) and specificity (85.7% and 88.4%) of HSV antigen detection in the CSF and sera, respectively, of the HSE and non-HSE groups. The ELISA method utilizing hyperimmune sera along with protein A for HSV antigen detection yielded good sensitivity and specificity in both CSF and sera, and hence can be useful for the diagnosis of HSE.