Japanese encephalitis virus isolation from mosquitoes during an outbreak in 2011 in Alappuzha district, Kerala.

mosquito-borne encephalitic flavivirus of rural eastern, southeastern and southern Asia. Outbreaks of JE have occurred in many states in India1. An explosive insular outbreak of meningoencephalitis, mainly in children, occurred during early 1996 in the Kuttanad area of Alappuzha district, Kerala2. During the outbreak in May 2011, 24 cases were recorded between January and May 2011; one in January, one in February, four in March, four in April, and 14 in May. The outbreak due to JE was diagnosed by the Centre for Research in Medical Entomology, Madurai, using JE MAC-ELISA kit obtained from National Institute of Virology, Pune (Unpublished data). We report here recovery of JEV from field collected mosquitoes during the outbreak. Out of 580 wild-caught mosquitoes from 124 pools tested for virus using antigen capture ELISA and an insect-bioassay (inoculation into Toxorhynchites splendens larvae and identification by IFA using Japanese encephalitis (JE) virus-specific monoclonal antibody), four flavivirus isolations were made, of which 2 (50%) were identified as JE virus, one each from Culex tritaeniorhynchus and Cx. gelidus. Kerala is an Indian state with a total area of 38,863 km2 and population of 31,838,619. Alappuzha lies at the western part of Kerala. It is the smallest district of the Kerala state. The latitude and longitude of Alappuzha district are 9°30′ N, 76o23′ E, respectively. Alappuzha district in Kerala was worst-affected with fever cases during May 2011. Mosquitoes were sampled on May 10–12, 2011 in Kuthirapanthi, Gynagiri, Ashramam, and Champakulam villages, the worst-affected areas of Alappuzha district. Adult mosquitoes were collected by hand catch method using aspirator and torch light. During dusk hours, mosquitoes were collected for one hour in and around cattlesheds (dusk collection). Indoor resting collections were done inside the human dwellings during 0800–1000 hrs (indoor collection). Outdoor resting mosquitoes were J Vector Borne Dis 50, September 2013, pp. 229–231