Seasonal occurrence of Japanese encephalitis vectors in Bareilly district, Uttar Pradesh, India

Background & objectives: Japanese encephalitis (JE) is one of the most common causes of acute encephalitis syndrome in many states of India. Uttar Pradesh state is well known for JE endemicity, contributing 75% of total cases during recent past. Several sporadic cases have been reported from Bareilly region of the state. The disease spread by bite of Culex mosquito. Survey of literature revealed no data on mosquito fauna with reference to JE in this region. Therefore, this study was planned to survey seasonal mosquito population and occurrence of JE vectors in Bareilly region. Methods: Mosquitoes were sampled on monthly basis from organized pig farm from February 2016 to January 2017 and identified using mosquito identification keys. The meteorological parameters of the area were obtained monthly and standard statistical methods were used to assess the relationship between different weather variables and mosquito population. Results: A total of 4337 mosquitoes belonging to five genera were collected. Mosquitoes of genus Culex were predominant and contributed 84.41% to the total catch. The most dominant species was Cx. tritaeniorhynchus (30.81%), followed by Cx. quinquefasciatus (28.50%), Cx. gelidus (17.24%), Cx. pseudovishnui (11.85%), Cx. vishnui (8.11%), Cx. fuscocephala (2.70%), Cx. infula (0.76%) and Cx. bitaeniorhynchus (0.03%). Pronounced seasonal variation was observed with majority of mosquitoes showing high density in monsoon and post-monsoon period. Interpretation & conclusion: The present study provides knowledge on distribution of JE vector in Bareilly which indicates that the area is at risk of JE outbreak. Abundance of Culex vector clearly demarcates possible threat of JE incidence in the study area. A long-term entomological study is needed to further evaluate the significant role of different weather variables in shaping mosquito densities.