Entomological factors in relation to the occurrence of Japanese encephalitis in Malkangiri district, Odisha State, India

ABSTRACT

Japanese encephalitis is a mosquito-borne arbo-viral disease with seasonal occurrence. Since 2009, AES/JE cases have been reported from Malkangiri district of Odisha State, India at an interval of one year.In the current study, the entomological parameters of known JE vector mosquito species were assessed for one year in Malkangiri district. Mosquito collections were done fortnightly in the index villages from August 2015 to July 2016 to record the density, their breeding habitats, feeding behaviour, parity, dusk index (DI) and infection status with JE virus. A total of 2347 JE vector mosquitoes belonging to nine species were collected from dusk collections. Culex vishnui (38.3%) was the predominant species followed by Cx. whitmorei (17.3%), Cx. fuscocephalus (13.6%), Cx. tritaeniorhynchus (11.1%), Cx. bitaeniorhynchus (6.1%), Anopheles subpictus (4.8%), An. barbirostris (4.4%), Cx. quinquefasciatus (2.3%) and Cx. gelidus (2.2%). The average DI of Cx. vishnui was 0.37 which was highest among all JE vector species and varied between 0.02 (April) and 0.9 (November). The human blood indexof Cx. vishnui was 0.026. A total of 1835 JE vector mosquitoes were screened for the isolation of JE virus, but none was found positive. Presence of paddy fields and ponds, abundance of JE vectors and their human feeding habit indicate the risk of JE transmission in the study area. Detection of JE virus in Cx. vishnui during 2016 outbreak in Malkangiri district further confirms that there would be a threat of JE transmission during the favourable period.

KEYWORDS:

• Culex vishnui
• entomological factors
• Japanese encephalitis virus
• Malkangiri
• Odisha

Acknowledgments

We acknowledge the facilities and support provided by the Director, ICMR-Vector Control Research Center, Puducherry. The authors thank NVBDCP, Bhubaneswar, Government of Odisha for financing this study. We also thank the Health authorities of Malkangiri district for extending their cooperation for carrying out the study. The authors are highly grateful to Dr. K. Gunasekaran, Head of the Vector Biology and Control Division, ICMR-VCRC, Puducherry for his constant support and encouragement. We acknowledge the staff members of the ICMR-Vector Control Research Center, Field Station, Koraput, for their technical assistance in laboratory and field works.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The study was funded by National Vector Borne Disease Control Programme, Odisha.