Usefulness of RT-PCR for the diagnosis of Japanese encephalitis in clinical samples.

The present study was carried out between July 2003 and December 2005 in PGIMER, Chandigarh, India and aimed to compare IgM capture ELISA and nested RT-PCR for the diagnosis of Japanese encephalitis (JE). The samples collected were cerebrospinal fluid and blood from 40 febrile patients with encephalitis (n=40, group I) and blood samples from febrile patients without encephalitis residing in JE endemic areas (n=45, group II). Overall, in CSF samples JE specific RNA was detected in 9/40 (22.5%), while 7/28 (25%) patients showed the presence of specific IgM antibodies. Only 28 CSF samples could be subjected to both RT-PCR and IgM and, among these, 13 cases were found to be confirmed JE based on IgM and/or RT-PCR positivity. Among the confirmed cases, 6 (6/13, 46.5%) could be detected by RT-PCR alone, 4 (4/13, 30.7%) by IgM capture ELISA and 3 (3/13, 23.1%) patients were positive by both the methods. All the RT-PCR positive cases had presented within 5 d of onset of illness. The serum samples of only 16 patients in group I could be tested for IgM antibodies and 5 (31.25%) were found to be positive, while in group II, 11.1% (5/45) positivity was observed. JE specific RNA could not be detected in serum samples of either group of patients. This study highlights the need for carrying out RT-PCR in CSF samples, compared to IgM antibody detection, for the early detection of JEV.