Seasonal abundance and infection of Japanese encephalitis vectors from Gorakhpur district, Uttar Pradesh, India

Background & objectives: Japanese encephalitis (JE) is a major public health problem in many states of India. Uttar Pradesh state contributes 75% of the total cases reported. A longitudinal study was undertaken to find out the seasonal abundance, infection in the JE vectors in Gorakhpur region of Uttar Pradesh, and intervention strategies like indoor residual spraying and long-lasting insecticidal nets were adopted. Methods: The vector abundance was monitored from July 2013 to August 2016 at fortnightly intervals and identified using standard mosquito identification keys and screened for viral infection. Intervention measures like indoor residual spraying with lambda-cyhalothrin 10% WP at 25 mg/m2 in 58 gramasabha in Bhathat Block and long-lasting insecticidal nets were distributed @ 2 LLIN for each household with 5-6 members in 5 villages of Korabar block. Results: A total of 5,36,609 mosquitoes constituting 34 species and 10 genera were collected during this study period. Among the JE vector, peak abundance of Culex tritaeniorhynchus was recorded just before the JE season from July to October in all the blocks. There was a marked reduction in the density of Cx. tritaeniorhynchus from July compared to baseline year 2014 in Bhathat Block where indoor residual spraying (IRS) was performed in June 2015. The vector density declined in 5 villages of Khorabar Block where long-lasting impregnated bed nets (LLINs) were distributed during July 2016. Interpretation & conclusion: The present study provided knowledge about the seasonal JE vector density and JE virus infection in mosquitoes during the monsoon season in Gorakhpur region of Uttar Pradesh. IRS and the personal protection measure like LLINs were distributed to interrupt the JE transmission in this area which gave encouraging results.