First outbreak of Japanese encephalitis in two villages of Dharmapuri district in Tamil Nadu

Background & objectives: Three cases of Japanese encephalitis (JE) were rep orted for the first time from two villages in Krishnagiri Health Unit distr ict of Tamil Nadu during November 1999, Two children died and one developed neurological sequelae. A serological survey was conducted in these village s to find out the prevalence of JE antibodies among children below 15 yr of age in addition to the epidemiological investigations. Methods: The prevalence of haemagglutination inhibiting (HI) antibodies to JE virus (JEV), West Nile virus (WNV) and dengue-2 virus (DEN-2) was detect ed by HI test and IgM antibody capture ELISA (MAC ELISA) was performed to d etermine recent infections with JE virus. Adult mosquitoes were collected i n the study villages and females of Culex pseudovishnui, C. tritaeniorhynch us and C. vishnui were tested for the presence of JE viral antigen by ELISA . Results : Out of 146 sera samples from children below 15 yr, the prevalence of HI antibodies to JEV, WNV and DEN-2 virus was found to be 8.9, 3.4 and 6.85 per cent respectively and three children had IgM antibodies to JEV. Of the 13 species of mosquitoes identified, C. tritaeniorhynchus (30.8%) was the most abundant species in the study villages. Two pools of female C, tri taeniorhynchus were found to be positive for JEV antigen. Fogging with 2 pe r cent pyrethrum and residual spray with 10 per cent cyfluthrin were effect ive in reducing vector density. Interpretation & conclusions: Serological investigations revealed that the JE virus was predominant in the study villages. In addition, DEN-2 and WN v iruses were also prevalent, Detection of JE virus specific IgM antibodies i n three specimens and the presence of JE viral antigen in 2 pools of C. tri taeniorhynchus emphasized the need for constant surveillance and monitoring so as to prevent future large outbreaks.