Ecology of Mosquito Vectors of Japanese Encephalitis Virus in Saharanpur District (JE Endemic Area), Uttar Pradesh State in Northern India

Abstract

This chapter presents results of 1 year (2005–2006) longitudinal study on the ecology of vectors of Japanese encephalitis virus carried out in two epidemiologically distinct situations in Saharanpur District (JE endemic area), Uttar Pradesh state, in Northern India to develop appropriate vector control/management strategy. The study revealed Cx. tritaeniorhynchus was the most abundant JE vector species that predominantly rested outdoors in vegetation and was found to change its resting habitat in accordance with the local agriculture practices. Paddy fields contributed approximately 5 % of total vector breeding, while rain water pools created by brick factories and hyacinth ponds together contributed 95 % of Cx. tritaeniorhynchus breeding in Saharanpur District. The differences between affected and unaffected villages of the district were a decreased abundance of Cx. tritaeniorhynchus mosquitoes during transmission period of the disease, presence of large fish pond and absence of brick factories in the unaffected villages. Saharanpur District has been reporting suspected cases of JE since 2002 and the outbreak of 2005 involved 221 cases of human encephalitis. In 2005, JE virus antigen was detected repeatedly from Cx. tritaeniorhynchus mosquitoes and vertical transmission of JE virus was established in 3 mosquito species (Cx. tritaeniorhynchus, Cx. vishnui and Cx. fuscocephala) in the district. When JE occurrence was analysed together with viral antigen detection (ELISA) in JE vectors, it was found that vertical transmission of JE virus occurred in two species, viz. Cx. tritaeniorhynchus and Cx. vishnui, 2 months prior to reporting of human encephalitis cases. This is an early warning signal for initiating integrated vector control measures to prevent JE outbreak.